Acacia senegal (L.) Willd.

Syn.: Acacia verek Guill. et Perr.
Mimosaceae
Gum Arabic, Senegal Gum, Sudan Gum Arabic, Kher, Kumta

Source: James A। Duke. 1983. Handbook of Energy Crops. unpublished.

Uses

Tree yields commercial gum arabic, used extensively in pharmaceutical preparations, inks, pottery pigments, water-colors, wax polishes, and liquid gum; for dressing fabrics, giving lustre to silk and crepe; for thickening colors and mordants in calico-printing; in confections and sweetmeats. Causing partial destruction of many alkaloids including atropine, hyoscyamine, scopolamine, homatropine, morphine, apomorphine, cocaine, and physostigmine, gum arabic might be viewed as a possible antidote. Pharmaceutically used mainly in the manufacture of emulsions and in making pills and troches (as an excipient); as demulcent for inflammations of the throat or stomach and as masking agent for acrid tasting substances such as capsicum; also as a film-forming agent in peel-off masks. Its major use is in foods, for example, as suspending or emulsifying agent, stabilizer, adhesive, flavor fixative, and to prevent crystallization of sugar, etc. Used in practically all categories of processed foods (candy, snack foods, alcoholic and nonalcoholic beverages, baked goods, frozen dairy desserts, gelatins, and puddings, imitation dairy products, breakfast cereals, and fats and oils). Use levels range from less than 0.004% (40 ppm) in soups and milk products, 0.7 to 2.9% in nonalcoholic beverages, imitation dairy, and snack foods, to as high as 45% in candy products (Leung, 1980). Strong rope made from bark fibers. White wood used for tool handles, black heartwood for weaver's shuttles. The long flexible strands of surface roots provide one of the strongest of local fibers, used for cordage, well-ropes, fishing nets, horsegirdles, footropes, etc. Seeds are dried and preserved for human consumption (NAS, 1980). Young foliage makes good forage. Plants useful for afforestation of arid tracts, soil reclamation, and windbreaks (Duke, 1981a). In modern pharmacy, it is commonly employed as a demulcent in preparations designed to treat diarrhea, dysentery, coughs, throat irritation, and fevers. It serves as an emulsifying agent and gives viscosity to powdered drug materials; is used as a binding agent in making pills and tablets and particularly cough drops and lozenges. Because of its enzyme, the gum is not suitable for use in products having readily oxidizable ingredients. For example, it reduces the vitamin A content of cod liver oil by 54% within three weeks. It is incompatible with aminopyrine, morphine, vanillin, phenol, thymol, a- and b-naphthol, guiacol, cresols, creosol, eugenol, apomorphine, eserine, epinephrine, isobarbaloin, gallic acid, and tannin; also with strongly alcoholic liquids, solutions of ferric chloride and lead subacetate and strong solutions of sodium borate. It was formerly given intravenously to counteract low blood pressure after hemorrhages and surgery and to treat edema associated with nephrosis, but such practices caused kidney and liver damage and allergic reactions and have been abandoned (Morton, 1977).

Folk Medicine

The demulcent, emollient gum is used internally in inflammation of intestinal mucosa, and externally to cover inflamed surfaces, as burns, sore nipples and nodular leprosy. Also said to be used for antitussive, astringent, catarrh, colds, coughs, diarrhea, dysentery, expectorant, gonorrhea, hemorrhage, sore throat, typhoid, urinary tract (Duke and Wain, 1981).

Chemistry

Gum acacia contains neutral sugars (rhamnose, arabinose, and galactose), acids (glucuronic acid and 4-methoxyglucuronic acid), calcium, magnesium, potassium, and sodium. Its complex structure is still not completely known. Its backbone chain consists of D-galactose units, and its side chains are composed of D-glucuronic acid units with l-rhamnose or l-arabinose as end units. The molecular weight has been reported to be between 200,000 to 300,000 and as high as 600,000 (Leung, 1980).

Toxicity

Ingested orally, acacia is nontoxic. However, some people are allergic to its dust and develop skin lesions and severe asthmatic attacks when in contact with it. Acacia can be digested by rats to an extent of 71%; guinea pigs and rabbits also seem to utilize it for energy, as does man to a certain extent. Gum arabic may actually elevate serum or tissue cholesterol levels in rats (Leung, 1980).

Description

Savanna shrub or tree, up to 20 m tall, over 1.3 m in girth, spiny; bark gray to brown or blackish, scaly, rough; young branchlets densely to sparsely pubescent, soon glabrescent, crown dense; stipules not spinescent; prickles just below the nodes, either in threes up to 7 mm long, with the middle one hooked downwards and the lateral ones curved upwards, or solitary with the laterals absent; leaves bioinnate, up to 2.5 cm long; leaf-axis finely downy with 2 glands; pinnae 6–20 pairs; leaflets small, 7–25 pairs, rigid, leathery, glabrous, linear to elliptic-oblong, ciliate on margins, pale glaucous-green, apex obtuse to subacute; flowers in spikes 5–10 cm long, not very dense, on peduncles 0.7–2 cm long, normally produced with the leaves; calyx bell-shaped, glabrous, deeply toothed; corolla white to yellowish, fragrant, sessile; pod straight or slightly curved, retrap-shaped, 7.5–18 cm long, 2.5 cm wide, thin, light brown or gray, papery or woody, firm, indehiscent, glabrous, 5–6-(-15) seeded; seeds greenish-brown. Fl. Jan.–Mar.; fr. Jan.–Apr., July, Aug. or Oct. (Duke, 1981a).

Germplasm

Tree with a single central stem and a dense flat-topped crown, bark without any papery peel, rough, gray or brown, with pubescent, rarely glabrous inflorescence, and pods variable in size, rounded to somewhat pointed but not rostrate or acuminate at apex. Variety rostrata Brenan is a shrub, branching at or close to base, or a small tree, with a single stem, 1–6 m tall, with dense flattened crown, bark normally with a flaking papery peel, creamy-yellow to yellow-green or gray-brown, inflorescence axis always pubescent and pods 2–3.5 times as long as wide, rostrate or acuminate at apex. Variety leiorhachis Brenan, is always a tree with central stem, and rounded or irregular with straggling branches; bark with conspicuous yellow papery peel, and inflorescence axis always glabrous. Variety pseudoglaucophylla occurs on fixed sand duned in Africa. Assigned to the African Center of Diversity, gum arabic is reported to exhibit tolerance to alkali, drought, fire, high pH, poor soil, sand, slope, and wind. (2n=26) (Duke, 1981a)

Distribution

Widespread in tropical Africa from Mozambique, Zambia to Somalia, Sudan, Ethiopia, Kenya, and Tanzania. Cultivated in India, Nigeria, and Pakistan.

Ecology

Thrives on dry rocky hills, in low-lying dry savannas, and areas where annual rainfall is 25–36 cm. This hardy species survives many adverse conditions, and seems to be favored by low rainfall and absence of frost. Ranging from Warm Temperate Thorn through Tropical Thorn to Tropical Dry Forest Life Zones, gum arabic is reported to tolerate annual precipitation of 3.8–22.8 dm (mean of 9 cases = 12.4 dm), annual mean temperature of 16.2–27.8°C (mean of 9 cases 23.8°C), and pH of 5.0–7.7 (mean of 7 cases = 6.4), but Cheema and Qadir (1973) report 7.4–8.2.

Cultivation

In Sudan, trees are cultivated over a very large area. Best propagated from seeds which are produced once every few years, grown in Sudan, in special "gum gardens." Elsewhere, it is collected from wild trees. In Pakistan, the best period for afforestation is the early monsoon season (Apr.–Jun.). Surface sowing is recommended in mildly alkaline sandy soils. Plants can also be reproduced by shoot cuttings. Trees coppice well (NAS, 1980).

Harvesting

Gum exudes froin cracks in bark of wild trees, mostly in the dry season, with little or none in the rainy season when flowers are out. In some areas, a long strip of bark is torn off and the gum allowed to exude. In Africa, it is regularly tapped from trees which are about 6 years old by making narrow transverse incisions in bark in February and March. In about a month, tears of gum form on surface and are gathered. Trees begin to bear between 4–18 years of age and are said to yield only when they are in unhealthy state due to poor soil, lack of moisture or damaged. Attempts to improve conditions tend to reduce yield. Gum from wild trees is variable and somewhat darker colored than that from cultivated plants. Collected gum is carefully freed of extraneous matter, sorted and sometimes ripened in sun before export. Gum arabic is oderless with a bland taste, yellowish and some tears are vermiform in shape. Ripened or bleached gum occurs in rounded or ovoid tears over 2.5 cm in diameter, and in broken fragments. Tears are nearly white or pale yellow and break readily with a glassy fracture. Gum is almost completely soluble in an equal volume of water and gives a translucent, viscous, slightly acid solution, but is insoluble in 90% alcohol. Kordofan (Sudan) Gum is yellow or pinkish, has fewer cracks and is more transparent (Duke, 1981a).

Yields and Economics

Annual yields from young trees may range from 188 to 2856 g (avg. 900 g), from older trees, 379 to 6754 g (avg. 2,000 g). Gum arabic is important export product for some areas in tropical Africa and Mauritania. From Africa some genuine gum is shipped to India then to Europe and America. Between 1940 and 1950, United States imports range from 3,179–8,989 MT (Duke, 1981a) Morton (1977) reports >11,000 MT more recently.

Energy

Considered the best firewood in Mauritius and Senegal, this is not a big yielder, annual running 0.5–5 m³/ha wood, with an energy value of ca 3,500 kcal/kg. A nitrogen,fixing species, it can be used to reestablish vegetation cover in degraded areas, as well as for sand-dune fixation and wind erosion control (NAS, 1980a).

Biotic Factors

Fungi reported on this crop are Cladosporium herbarum, Fusarum sp., Ravenelia acaciae-senegalae and R. acaciocola. Many insect visitors mimic the plant, the buffalo treehopper, Stictocephala bisonia, being a good example. Spiders (Cyclops sp.) may completely cover the young growing apex. Seedlings are often grazed by gazelles, goats, and pigs (Morton, 1977).

References

• Cheema, M.S.Z.A. and Qadir, S.A. 1973. Autecology of Acacia senegal (L.) Willd. Vegetatio Vol. 27(1–3):131–162.
  
• Duke, J.A. 1981a. Handbook of legumes of world economic importance. Plenum Press. NewYork.
  
• Duke, J.A. and Wain, K.K. 1981. Medicinal plants of the world. Computer index with more than 85,000 entries. 3 vols.
  
• Leung, A.Y. 1980. Encyclopedia of common natural ingredients used in food, drugs, and cosmetics. John Wiley & Sons. New York.
  
• Morton, J.F. 1977. Major medicinal plants. C.C. Thomas, Springfield, IL.
  
• N.A.S. 1980a. Firewood crops. Shrub and tree species for energy production. National Academy of Sciences, Washington, DC.

Acacia saligna (Labill.) H.Wendl

Uses

Orange wattle is an extremely rugged tree, adaptable to barren slopes, derelict land, and exceptionally arid conditions in Australia and North Africa. It grows rapidly and is used for reclaiming eroded hillsides and wastelands and for stabilizing drift sands as well as for fuel. This is one of the best woody species for binding moving sand. It is useful for windbreaks, amenity plantings, beautification projects, and roadside stabilization in semiarid regions. The leaves, or phyllodes, are palatable to livestock when fresh or dried into hay, especially used as supplementary feed for sheep and goats. Crushed seeds have been fed to sheep without ill effects. Regrowth of established bushes is so good that Acacia saligna can be completely grazed off without harming the plants. The damaged bark exudes copious amounts of a very acidic gum that seems to show promise for use in pickles and other acidic foodstuffs (NAS, 1980).

Folk Medicine

No data observed.

Chemistry

Natal-grown bark contains up to 30.3% tannin compared to 19.1–23.0 at the Cape. The plant has given negative test for HCN.

Description

Dense, bushy shrub, usually 2–5 m tall; may grow treelike to 8 m tall with a single main stem (diameter to 30 cm). In spring its usually drooping branches are clad in beautiful and abundant yellow flowers (NAS, 1980a).

Germplasm

Reported from the Australian Center of Diversity, orange wattle, or cvs thereof, is reported to tolerate alkalinity, drought, heavy soil, poor soil, salinity, salt spray, sand, shade, slope, waterlogging, and weeds. (2n = 26)

Distribution

Acacia saligna is native to the southwestern corner of western Australia. It was introduced to South Africa in the 1840s in an attempt to stabilize the shifting sand dunes. It has also been planted in Uruguay, Mexico Israel, Iran, Iraq, Jordan, Syria, Greece, Cyprus, and North African countries (NAS, 1980a).

Ecology

Acacia saligna can grow throughout the tropical and the warm temperate regions of the world (NAS, 1980a). In its native habitat, the summer temperature ranges from about 23°–36°C, winter temperatures from 4°–9°C. The plant does not withstand frost and grows best where the winter and summer means are between 13° and 30°C respectively. Grows from near sea level to about 300 m, with isolated occurrences at higher elevations. Particularly drought hardy, it grows where annual rainfall is as low as 250 mm, though it probably does better with 350–600 mm. It grows well where annual rainfall is as high as 1,000 mm. Grows mainly on sandy, coastal plains, but is found from swampy sites and riverbanks to small, rocky hills (often granitic) and coastal slopes. It occurs on poor acid or calcareous sands, under the most dry and adverse soil conditions, in moderately heavy clays and a range of podzols (NAS, 1980a).

Cultivation

Seeds germinate readily; young plants can often be found under mature trees in the hundreds. Seedlings are easily raised in a nursery and established in the field. This species develops root suckers and coppices freely. Seeds are normally treated with boiling water, but nicking the seed coat, soaking in sulfuric acid, and exposing the seeds to dry heat are also effective (NAS, 1980a).

Harvesting

In Mediterranean countries, the fuelwood from this species is harvested on a coppice rotation system of 5–10 years (NAS, 1980).

Yields and Economics

Acacia saligna grows quickly, often reaching up to 8 m tall with a spread as great as its height in just 4 or 5 years. In very dry situations, growth rate is slower. Annual yields vary from 1.5 to 10 m³ per ha, depending on site. Because of its hardiness and profuse reproductive abilities, Acacia saligna has become a serious menace in parts of South Africa by invading and displacing indigenous vegetation. It infests water courses (sometimes decreasing the water available for irrigation), and has proved difficult to eradicate (NAS, 1980a).

Energy

Plantations for fuel have been established in some Mediterranean countries. But, according to one report from South Africa, the wood is "sappy, light, and not a popular fuelwood." The plant can withstand some shade and can be grown as an understory beneath pines or eucalypts in energy plantations or village fuel and fodder areas (NAS, 1980a). The annual litterfall of four Acacia species naturalized in the South African Cape, comprising 60% foliage and 30% reproductive structures, averages 7 MT/ha, double the value expected in evergreen scrub communities in winter rainfall regions.

Biotic Factors

Acacia saligna supports a diverse and abundant range of herbivores that cause damage to the plant. Among pests cited are Icerya purchasi (Hemiptera) and Euproctis fasciata (Lepidoptera) (NAS, 1980a) and Meloidgogyne sp. (Nematoda)

References

• N.A.S. 1980a. Firewood crops. Shrub and tree species for energy production. National Academy of Sciences, Washington, DC.

Acacia senegal (L.) Willd.

Syn.: Acacia verek Guill. et Perr.
Mimosaceae
Gum Arabic, Senegal Gum, Sudan Gum Arabic, Kher, Kumta

Source: James A। Duke. 1983. Handbook of Energy Crops. unpublished.

Uses

Tree yields commercial gum arabic, used extensively in pharmaceutical preparations, inks, pottery pigments, water-colors, wax polishes, and liquid gum; for dressing fabrics, giving lustre to silk and crepe; for thickening colors and mordants in calico-printing; in confections and sweetmeats. Causing partial destruction of many alkaloids including atropine, hyoscyamine, scopolamine, homatropine, morphine, apomorphine, cocaine, and physostigmine, gum arabic might be viewed as a possible antidote. Pharmaceutically used mainly in the manufacture of emulsions and in making pills and troches (as an excipient); as demulcent for inflammations of the throat or stomach and as masking agent for acrid tasting substances such as capsicum; also as a film-forming agent in peel-off masks. Its major use is in foods, for example, as suspending or emulsifying agent, stabilizer, adhesive, flavor fixative, and to prevent crystallization of sugar, etc. Used in practically all categories of processed foods (candy, snack foods, alcoholic and nonalcoholic beverages, baked goods, frozen dairy desserts, gelatins, and puddings, imitation dairy products, breakfast cereals, and fats and oils). Use levels range from less than 0.004% (40 ppm) in soups and milk products, 0.7 to 2.9% in nonalcoholic beverages, imitation dairy, and snack foods, to as high as 45% in candy products (Leung, 1980). Strong rope made from bark fibers. White wood used for tool handles, black heartwood for weaver's shuttles. The long flexible strands of surface roots provide one of the strongest of local fibers, used for cordage, well-ropes, fishing nets, horsegirdles, footropes, etc. Seeds are dried and preserved for human consumption (NAS, 1980). Young foliage makes good forage. Plants useful for afforestation of arid tracts, soil reclamation, and windbreaks (Duke, 1981a). In modern pharmacy, it is commonly employed as a demulcent in preparations designed to treat diarrhea, dysentery, coughs, throat irritation, and fevers. It serves as an emulsifying agent and gives viscosity to powdered drug materials; is used as a binding agent in making pills and tablets and particularly cough drops and lozenges. Because of its enzyme, the gum is not suitable for use in products having readily oxidizable ingredients. For example, it reduces the vitamin A content of cod liver oil by 54% within three weeks. It is incompatible with aminopyrine, morphine, vanillin, phenol, thymol, a- and b-naphthol, guiacol, cresols, creosol, eugenol, apomorphine, eserine, epinephrine, isobarbaloin, gallic acid, and tannin; also with strongly alcoholic liquids, solutions of ferric chloride and lead subacetate and strong solutions of sodium borate. It was formerly given intravenously to counteract low blood pressure after hemorrhages and surgery and to treat edema associated with nephrosis, but such practices caused kidney and liver damage and allergic reactions and have been abandoned (Morton, 1977).

Folk Medicine

The demulcent, emollient gum is used internally in inflammation of intestinal mucosa, and externally to cover inflamed surfaces, as burns, sore nipples and nodular leprosy. Also said to be used for antitussive, astringent, catarrh, colds, coughs, diarrhea, dysentery, expectorant, gonorrhea, hemorrhage, sore throat, typhoid, urinary tract (Duke and Wain, 1981).

Chemistry

Gum acacia contains neutral sugars (rhamnose, arabinose, and galactose), acids (glucuronic acid and 4-methoxyglucuronic acid), calcium, magnesium, potassium, and sodium. Its complex structure is still not completely known. Its backbone chain consists of D-galactose units, and its side chains are composed of D-glucuronic acid units with l-rhamnose or l-arabinose as end units. The molecular weight has been reported to be between 200,000 to 300,000 and as high as 600,000 (Leung, 1980).

Toxicity

Ingested orally, acacia is nontoxic. However, some people are allergic to its dust and develop skin lesions and severe asthmatic attacks when in contact with it. Acacia can be digested by rats to an extent of 71%; guinea pigs and rabbits also seem to utilize it for energy, as does man to a certain extent. Gum arabic may actually elevate serum or tissue cholesterol levels in rats (Leung, 1980).

Description

Savanna shrub or tree, up to 20 m tall, over 1.3 m in girth, spiny; bark gray to brown or blackish, scaly, rough; young branchlets densely to sparsely pubescent, soon glabrescent, crown dense; stipules not spinescent; prickles just below the nodes, either in threes up to 7 mm long, with the middle one hooked downwards and the lateral ones curved upwards, or solitary with the laterals absent; leaves bioinnate, up to 2.5 cm long; leaf-axis finely downy with 2 glands; pinnae 6–20 pairs; leaflets small, 7–25 pairs, rigid, leathery, glabrous, linear to elliptic-oblong, ciliate on margins, pale glaucous-green, apex obtuse to subacute; flowers in spikes 5–10 cm long, not very dense, on peduncles 0.7–2 cm long, normally produced with the leaves; calyx bell-shaped, glabrous, deeply toothed; corolla white to yellowish, fragrant, sessile; pod straight or slightly curved, retrap-shaped, 7.5–18 cm long, 2.5 cm wide, thin, light brown or gray, papery or woody, firm, indehiscent, glabrous, 5–6-(-15) seeded; seeds greenish-brown. Fl. Jan.–Mar.; fr. Jan.–Apr., July, Aug. or Oct. (Duke, 1981a).

Germplasm

Tree with a single central stem and a dense flat-topped crown, bark without any papery peel, rough, gray or brown, with pubescent, rarely glabrous inflorescence, and pods variable in size, rounded to somewhat pointed but not rostrate or acuminate at apex. Variety rostrata Brenan is a shrub, branching at or close to base, or a small tree, with a single stem, 1–6 m tall, with dense flattened crown, bark normally with a flaking papery peel, creamy-yellow to yellow-green or gray-brown, inflorescence axis always pubescent and pods 2–3.5 times as long as wide, rostrate or acuminate at apex. Variety leiorhachis Brenan, is always a tree with central stem, and rounded or irregular with straggling branches; bark with conspicuous yellow papery peel, and inflorescence axis always glabrous. Variety pseudoglaucophylla occurs on fixed sand duned in Africa. Assigned to the African Center of Diversity, gum arabic is reported to exhibit tolerance to alkali, drought, fire, high pH, poor soil, sand, slope, and wind. (2n=26) (Duke, 1981a)

Distribution

Widespread in tropical Africa from Mozambique, Zambia to Somalia, Sudan, Ethiopia, Kenya, and Tanzania. Cultivated in India, Nigeria, and Pakistan.

Ecology

Thrives on dry rocky hills, in low-lying dry savannas, and areas where annual rainfall is 25–36 cm. This hardy species survives many adverse conditions, and seems to be favored by low rainfall and absence of frost. Ranging from Warm Temperate Thorn through Tropical Thorn to Tropical Dry Forest Life Zones, gum arabic is reported to tolerate annual precipitation of 3.8–22.8 dm (mean of 9 cases = 12.4 dm), annual mean temperature of 16.2–27.8°C (mean of 9 cases 23.8°C), and pH of 5.0–7.7 (mean of 7 cases = 6.4), but Cheema and Qadir (1973) report 7.4–8.2.

Cultivation

In Sudan, trees are cultivated over a very large area. Best propagated from seeds which are produced once every few years, grown in Sudan, in special "gum gardens." Elsewhere, it is collected from wild trees. In Pakistan, the best period for afforestation is the early monsoon season (Apr.–Jun.). Surface sowing is recommended in mildly alkaline sandy soils. Plants can also be reproduced by shoot cuttings. Trees coppice well (NAS, 1980).

Harvesting

Gum exudes froin cracks in bark of wild trees, mostly in the dry season, with little or none in the rainy season when flowers are out. In some areas, a long strip of bark is torn off and the gum allowed to exude. In Africa, it is regularly tapped from trees which are about 6 years old by making narrow transverse incisions in bark in February and March. In about a month, tears of gum form on surface and are gathered. Trees begin to bear between 4–18 years of age and are said to yield only when they are in unhealthy state due to poor soil, lack of moisture or damaged. Attempts to improve conditions tend to reduce yield. Gum from wild trees is variable and somewhat darker colored than that from cultivated plants. Collected gum is carefully freed of extraneous matter, sorted and sometimes ripened in sun before export. Gum arabic is oderless with a bland taste, yellowish and some tears are vermiform in shape. Ripened or bleached gum occurs in rounded or ovoid tears over 2.5 cm in diameter, and in broken fragments. Tears are nearly white or pale yellow and break readily with a glassy fracture. Gum is almost completely soluble in an equal volume of water and gives a translucent, viscous, slightly acid solution, but is insoluble in 90% alcohol. Kordofan (Sudan) Gum is yellow or pinkish, has fewer cracks and is more transparent (Duke, 1981a).

Yields and Economics

Annual yields from young trees may range from 188 to 2856 g (avg. 900 g), from older trees, 379 to 6754 g (avg. 2,000 g). Gum arabic is important export product for some areas in tropical Africa and Mauritania. From Africa some genuine gum is shipped to India then to Europe and America. Between 1940 and 1950, United States imports range from 3,179–8,989 MT (Duke, 1981a) Morton (1977) reports >11,000 MT more recently.

Energy

Considered the best firewood in Mauritius and Senegal, this is not a big yielder, annual running 0.5–5 m³/ha wood, with an energy value of ca 3,500 kcal/kg. A nitrogen,fixing species, it can be used to reestablish vegetation cover in degraded areas, as well as for sand-dune fixation and wind erosion control (NAS, 1980a).

Biotic Factors

Fungi reported on this crop are Cladosporium herbarum, Fusarum sp., Ravenelia acaciae-senegalae and R. acaciocola. Many insect visitors mimic the plant, the buffalo treehopper, Stictocephala bisonia, being a good example. Spiders (Cyclops sp.) may completely cover the young growing apex. Seedlings are often grazed by gazelles, goats, and pigs (Morton, 1977).

References

• Cheema, M.S.Z.A. and Qadir, S.A. 1973. Autecology of Acacia senegal (L.) Willd. Vegetatio Vol. 27(1–3):131–162.
  
• Duke, J.A. 1981a. Handbook of legumes of world economic importance. Plenum Press. NewYork.
  
• Duke, J.A. and Wain, K.K. 1981. Medicinal plants of the world. Computer index with more than 85,000 entries. 3 vols.
  
• Leung, A.Y. 1980. Encyclopedia of common natural ingredients used in food, drugs, and cosmetics. John Wiley & Sons. New York.
  
• Morton, J.F. 1977. Major medicinal plants. C.C. Thomas, Springfield, IL.
  
• N.A.S. 1980a. Firewood crops. Shrub and tree species for energy production. National Academy of Sciences, Washington, DC.

Acacia saligna (Labill.) H.Wendl

Uses

Orange wattle is an extremely rugged tree, adaptable to barren slopes, derelict land, and exceptionally arid conditions in Australia and North Africa. It grows rapidly and is used for reclaiming eroded hillsides and wastelands and for stabilizing drift sands as well as for fuel. This is one of the best woody species for binding moving sand. It is useful for windbreaks, amenity plantings, beautification projects, and roadside stabilization in semiarid regions. The leaves, or phyllodes, are palatable to livestock when fresh or dried into hay, especially used as supplementary feed for sheep and goats. Crushed seeds have been fed to sheep without ill effects. Regrowth of established bushes is so good that Acacia saligna can be completely grazed off without harming the plants. The damaged bark exudes copious amounts of a very acidic gum that seems to show promise for use in pickles and other acidic foodstuffs (NAS, 1980).

Folk Medicine

No data observed.

Chemistry

Natal-grown bark contains up to 30.3% tannin compared to 19.1–23.0 at the Cape. The plant has given negative test for HCN.

Description

Dense, bushy shrub, usually 2–5 m tall; may grow treelike to 8 m tall with a single main stem (diameter to 30 cm). In spring its usually drooping branches are clad in beautiful and abundant yellow flowers (NAS, 1980a).

Germplasm

Reported from the Australian Center of Diversity, orange wattle, or cvs thereof, is reported to tolerate alkalinity, drought, heavy soil, poor soil, salinity, salt spray, sand, shade, slope, waterlogging, and weeds. (2n = 26)

Distribution

Acacia saligna is native to the southwestern corner of western Australia. It was introduced to South Africa in the 1840s in an attempt to stabilize the shifting sand dunes. It has also been planted in Uruguay, Mexico Israel, Iran, Iraq, Jordan, Syria, Greece, Cyprus, and North African countries (NAS, 1980a).

Ecology

Acacia saligna can grow throughout the tropical and the warm temperate regions of the world (NAS, 1980a). In its native habitat, the summer temperature ranges from about 23°–36°C, winter temperatures from 4°–9°C. The plant does not withstand frost and grows best where the winter and summer means are between 13° and 30°C respectively. Grows from near sea level to about 300 m, with isolated occurrences at higher elevations. Particularly drought hardy, it grows where annual rainfall is as low as 250 mm, though it probably does better with 350–600 mm. It grows well where annual rainfall is as high as 1,000 mm. Grows mainly on sandy, coastal plains, but is found from swampy sites and riverbanks to small, rocky hills (often granitic) and coastal slopes. It occurs on poor acid or calcareous sands, under the most dry and adverse soil conditions, in moderately heavy clays and a range of podzols (NAS, 1980a).

Cultivation

Seeds germinate readily; young plants can often be found under mature trees in the hundreds. Seedlings are easily raised in a nursery and established in the field. This species develops root suckers and coppices freely. Seeds are normally treated with boiling water, but nicking the seed coat, soaking in sulfuric acid, and exposing the seeds to dry heat are also effective (NAS, 1980a).

Harvesting

In Mediterranean countries, the fuelwood from this species is harvested on a coppice rotation system of 5–10 years (NAS, 1980).

Yields and Economics

Acacia saligna grows quickly, often reaching up to 8 m tall with a spread as great as its height in just 4 or 5 years. In very dry situations, growth rate is slower. Annual yields vary from 1.5 to 10 m³ per ha, depending on site. Because of its hardiness and profuse reproductive abilities, Acacia saligna has become a serious menace in parts of South Africa by invading and displacing indigenous vegetation. It infests water courses (sometimes decreasing the water available for irrigation), and has proved difficult to eradicate (NAS, 1980a).

Energy

Plantations for fuel have been established in some Mediterranean countries. But, according to one report from South Africa, the wood is "sappy, light, and not a popular fuelwood." The plant can withstand some shade and can be grown as an understory beneath pines or eucalypts in energy plantations or village fuel and fodder areas (NAS, 1980a). The annual litterfall of four Acacia species naturalized in the South African Cape, comprising 60% foliage and 30% reproductive structures, averages 7 MT/ha, double the value expected in evergreen scrub communities in winter rainfall regions.

Biotic Factors

Acacia saligna supports a diverse and abundant range of herbivores that cause damage to the plant. Among pests cited are Icerya purchasi (Hemiptera) and Euproctis fasciata (Lepidoptera) (NAS, 1980a) and Meloidgogyne sp. (Nematoda)

References

• N.A.S. 1980a. Firewood crops. Shrub and tree species for energy production. National Academy of Sciences, Washington, DC.

New Arid Land Ornamentals

Over the past decade, water conservation has become an increasingly important issue across the southwestern United States. This concern has led local horticulturists and landscape architects to explore the use of water-thrifty ornamentals from dry climates throughout the world. The Chihuahuan and Sonoran deserts in particular have yielded a vast array of successful landscape plants. Universities, growers, and plant enthusiasts have all participated in the collection, propagation, evaluation, and promotion of new plant introductions. A group of recent proven introductions, including trees, shrubs, ground covers, and perennials are included below with information on their origins, growth habits, cultural requirements, and potential uses in the landscape.

Acacia redolens Maslin, Desert Carpet^TM

Native to inland areas of Western Australia, Acacia redolens Maslin has been used extensively in southern California and Arizona to cover large areas inexpensively. Seedlings of Acacia redolens vary widely in their growth habits, often reaching heights in excess of 1.8 m (6 feet). The Desert Carpet™ clone was selected from the first Phoenix freeway plantings for its prostrate growth habit, and was released by Mountain States Wholesale Nursery in 1984. Since that time, this groundcover has performed consistently on many projects, and years after installation has maintained a height of only 0.6 m (24 inches). One plant can spread to a width of 3.6 m (12 feet), although we have observed that the cutting-grown Desert Carpet™ plants are slower to establish and reach their mature size than seedlings. The slower growth rate and prostrate nature of this clone should reduce maintenance costs, since pruning is not necessary to control vertical growth. Instead of true leaves, Acacia redolens has thick, leathery, gray-green phyllodes. This plant blooms in the spring with small yellow flowers. Freeway acacia will tolerate low temperatures of –11.1° to –9.4°C (12°–15°F), alkaline and slightly saline soils, and does not seem to be choosy about soil types. In coastal areas it requires little or no supplemental irrigation, but does require regular irrigation in hot desert regions. Desert Carpet^TM seems to be disease and pest free.

Baccharis hybrid 'Starn' (P.P.A.F.) Thompson^TM

When Dr. Tommy Thompson and Dr. Chi Won Lee of the University of Arizona released Baccharis hybrid 'Centennial', it filled a great void in our plant palette. Their research has been carried on, and now the improved Thompson™ clone is available. Since Baccharis 'Centennial' is a female plant, it has two undesirable characteristics. First, it produces pappus, or white "fluff," which litters the landscape and reduces the esthetic appearance of the plants for a short period of time. Also, since 'Centennial' is a female plant, it can be pollinated by nearby male Baccharis sarothroides Gray (Desert broom), and seedlings often result. This is why you sometimes see stands of 'Centennial' with taller Baccharis plants growing up through them. The Thompson^TM clone is a male plant, eliminating these two negative characteristics. Also, Thompson^TM was selected from the next generation after 'Centennial', and has 25% more Baccharis sarothroides for heat and disease resistance. The growth habits and uses of these two clones are essentially the same: both grow to about 0.9 m (3 feet) tall by 1.2–1.5 m (4-5) feet wide, are evergreen with bright green foliage and inconspicuous flowers, and provide a low-maintenance, long-lived alternative for difficult locations.

Cercidium species 'Desert Museum'

This hybrid palo verde is a three-way cross between Parkinsonia aculeata L., Cercidium microphyllum (Torr.) Rose & I.M. Johnst., and Cercidium floridum Benth. ex Gray, and seems to combine the best qualities of all three plants. 'Desert Museum' grows very rapidly to 6.1 m (20 feet) tall and wide in 3 to 5 years, after which it needs little or no irrigation. It is completely thornless, and produces very little litter, with few seed pods. It has a sturdy, upright growth habit which requires very little pruning or staking. It blooms over a long period of time, with the heaviest bloom from about mid-March to May 1. It also tends to bloom again in June and August. The yellow flowers are larger than any of its three "parents." It does not reseed like the messy Parkinsonia aculeata!

Chilopsis linearis (Cav.) Sweet, Lucretia Hamilton^TM

Desert willow trees occur along washes throughout the southwestern US and northern Mexico. This small deciduous tree has narrow, light green leaves that give it a weeping appearance. In the summer, the tree is covered with fragrant, trumpet-shaped flowers. In the wild, the flower colors range from white to purple, although a pale pink to lavender flower color is the most common. The Lucretia Hamilton^TM clone was selected for its intense, deep pink to purple flower color, as well as its small stature. While many desert willow trees can grow to 7.6 m (25 feet) tall and wide, this clone seems to stay below 5.4–6.1 m (18-20 feet) tall and wide. After flowering, long narrow seed pods are produced. Plant Chilopsis linearis in full sun and well-drained soil, and in regions where temperatures do not drop below –17.8°C (0°F).

Chrysactinia mexicana Gray (Damianita)

This small, compact shrub grows to 0.6 m (2 feet) tall and wide, and bears a very strong resemblance to turpentine bush, with needle-like green leaves and yellow daisy-like flowers. However, damianita blooms from March to September, while turpentine bush blooms from September to November. Combining the two plants would be a great way to prolong the color display! Damianita has wonderful-smelling foliage, and would be a great selection for sensory gardens. Damianita is a very tough, durable plant, tolerating extreme heat and cold, down to –17.8°C (0°F). Plant in full sun, and almost any soil. If this plant starts to look woody, prune it back severely in the early spring. Damianita ranges from New Mexico to west Texas and northeastern Mexico, at elevations of 609–2134 m (2000–7000 feet).

Dalea capitata Sierra Gold^TM

This well-behaved ground cover grows to about 20 cm (8 inches) tall by 0.9 m (3 feet) wide. Because of its compact size, Sierra Gold^TM is a good selection for tight planting areas, such as small planters or medians. Its fine-textured, light green foliage has a fresh, lemony scent. Rabbits seem to avoid it! Yellow flowers carpet Sierra Gold^TM in the spring and the fall. This plant is hardy to at least –15°C (5°F), but it will be deciduous at –3.9°C (25°F). The one drawback to this plant is that the whiteflies seem to like it, so some insecticide applications will be necessary in heavily infested areas around Phoenix. Plant in full sun for best results. No soil amendments should be necessary. In hot desert regions this plant requires some supplemental irrigation from spring to fall. Although most dales native to Arizona and Mexico tend to rot out if overwatered, we have observed this plant thriving right next to turfgrass, where it receives heavy irrigation. More testing is needed to determine if it will tolerate coastal areas, or regions with high rainfall.

Dasylirion longissimum

This user-friendly accent plant is a great selection for high-traffic areas such as walkways and near entries. This grasslike plant does well in containers, and its symmetrical form provides a striking focal point. Its thin, stiff green leaves are completely unarmed, and have smooth edges. Eventually, its single trunk can grow to 1.8 m (6 feet), topped by a 1.5 m- (5-foot-) wide rounded head of leaves. The older, bottom leaves can be trimmed off to expose the trunk. Dasylirion longissimum is native to Mexico, and is hardy to about –8.3°C (17°F).

Euphorbia biglandulosa Desf. (Gopher Plant)

This evergreen perennial or subshrub has a very unusual form and appearance. Its arching stems angle out and up, and can reach a length of 0.6 m (2 feet). The plant grows to 0.9 m (3 feet) tall by 1.2 m (4 feet) across; with narrow, fleshy grey-green leaves. Broad clusters of chartreuse flowers occur at the tips of the arching stems, usually in the late winter and early spring. Flowers are followed by small brown seed pods that explode upon ripening. The stems usually die back after fruiting, leaving a small clump of grey-green foliage near the ground. Plant Euphorbia biglandulosa in full sun or light shade, in a well-draining soil. It is cold hardy to –15°C (5°F).

Hesperaloe parviflora (Torr.) J. Coult., 'Yellow' (Yellow yucca)

A clumping perennial with long, gray-green leaves, Hesperaloe parviflora grows slowly to form a grasslike clump 1.0–1.2 m (3–4 feet) tall and wide. From spring through fall, it produces 1.5 m- (5-foot-) tall flower spikes. Red-flowering plants have been a staple in southwestern landscapes for many years. This is simply a yellow-flowering selection. Use this tough accent plant in full sun. Since it also tolerates reflected heat, yellow yucca is a reliable plant to use along sidewalks, in parking lots, etc. Tolerant of temperature extremes, yellow yucca is cold-hardy to at least –17.8°C (0°F). Once established, it requires little or no irrigation. All in all, yellow yucca is one of the toughest and most maintenance-free plants.

Hymenoxys acaulis (Pursh) K. Parker (Angelita Daisy)

This perennial is native to the southwestern US, where it occurs most often at elevations from 1219–2134 m (4000–7000 feet), on dry rocky slopes and mesas. Angelita daisy bears a strong resemblance to Baileya multiradiata Harv. & A. Gray ex Torr. (desert marigold). However, the foliage is green rather than gray, and the flower is a deeper gold color. Forming rounded clumps to fifteen inches tall and wide, Hymenoxys acaulis is a wonderful plant to use as a border in front of larger shrubs. I f water is available, it will naturalize in the landscape. In Phoenix, this plant blooms all year, with especially heavy bloom in the spring and fall months. This prolonged bloom period results in many dried flower stalks, which can make the plants look scruffy. We recommend cutting off the old flower spikes occasionally to rejuvenate the plant and initiate new flower production. Angelita daisy seems to prefer well-drained soils and full sun. It is very cold hardy, heat tolerant, and drought tolerant.

Leucophyllum candidum I.M. Johnst. Thunder Cloud^TM

As with all of the other Leucophyllum species, this clone blooms when the humidity is high. The silver, pubescent foliage is a perfect foil for the masses of indigo flowers that appear in the summer and fall months. Thunder Cloud^TM was selected and trademarked by Benny Simpson of Texas A&M University. His clone is highly valued because of its small, dense growth habit. Unlike most of the larger Leucophyllum species, Thunder Cloud^TM remains reliably small, to three feet tall and wide. This plant is cold hardy to at least –12.2°C (10°F). Plant all of the Leucophyllum species in full sun and well-drained soil. Avoid overwatering.

Leucophyllum langmaniae Rio Bravo^TM

Trademarked by Mountain States Nursery, this clone has a nice, compact growth habit very similar to L. frutescens 'Compacta'. Rio Bravo^TM has become very popular because of its bright green foliage and rounded, dense form. It has lavender flowers and will eventually grow to 1.5 m (5 feet) tall and wide. Like the L. candidum species, it requires well-drained soils and full sun. It is hardy to –12.2°C (10°F).

Muhlenbergia capillaris (Lam.) Trin. Regal Mist^TM

We feel that this ornamental grass shows great promise for many different regions of the country. Native to humid southeastern Texas, this grass has adapted extremely well to the hot, dry conditions of deserts in Arizona and Nevada. In fact, it has performed incredibly well in Las Vegas, which is cursed with poor soils, high winds, high summer temperatures, and cold winters. Regal Mist^TM is also happy in heavy soils, with ample irrigation. In short, it has worked everywhere it has been tried, so far! It is hardy to at least –17.8°C (0°F). Regal Mist^TM has narrow, dark green, glossy leaves. It grows quickly to form a rounded clump to 0.9 m (3 feet) tall and wide. The flower spikes on this grass have attracted a lot of attention... they form misty masses of pink to purple flowers in October and November. We recommend cutting this plant back in early spring to cut off the dead flower spikes and any dormant foliage.

Penstemon species

There are so many wonderful Penstemon species to try in the garden, that is difficult to select just a few. Most of the penstemons are perennials with a basal rosette of foliage, which send up spikes of tubular flowers in the spring and early summer. They add incredible color to the landscape, and attract hummingbirds as well! Penstemons come in a wide range of colors, including blue, purple, pink, and red. After they finish blooming, allow the flower spikes to dry on the plant. Then cut off the spikes and sprinkle the seed in the garden to increase next year's mass of color. There are two new species to try: Penstemon triflorus Heller, which has short, 46 cm (18 inch) spikes of dark pink-purple flowers which occur along the stem in clusters of three; and Penstemon clevelandii Gray, native to southern and Baja California, with spikes of clear, bright pink flowers to 0.6–0.8 m (2–2.5 feet) tall.

New Arid Land Ornamentals

Over the past decade, water conservation has become an increasingly important issue across the southwestern United States. This concern has led local horticulturists and landscape architects to explore the use of water-thrifty ornamentals from dry climates throughout the world. The Chihuahuan and Sonoran deserts in particular have yielded a vast array of successful landscape plants. Universities, growers, and plant enthusiasts have all participated in the collection, propagation, evaluation, and promotion of new plant introductions. A group of recent proven introductions, including trees, shrubs, ground covers, and perennials are included below with information on their origins, growth habits, cultural requirements, and potential uses in the landscape.

Acacia redolens Maslin, Desert Carpet^TM

Native to inland areas of Western Australia, Acacia redolens Maslin has been used extensively in southern California and Arizona to cover large areas inexpensively. Seedlings of Acacia redolens vary widely in their growth habits, often reaching heights in excess of 1.8 m (6 feet). The Desert Carpet™ clone was selected from the first Phoenix freeway plantings for its prostrate growth habit, and was released by Mountain States Wholesale Nursery in 1984. Since that time, this groundcover has performed consistently on many projects, and years after installation has maintained a height of only 0.6 m (24 inches). One plant can spread to a width of 3.6 m (12 feet), although we have observed that the cutting-grown Desert Carpet™ plants are slower to establish and reach their mature size than seedlings. The slower growth rate and prostrate nature of this clone should reduce maintenance costs, since pruning is not necessary to control vertical growth. Instead of true leaves, Acacia redolens has thick, leathery, gray-green phyllodes. This plant blooms in the spring with small yellow flowers. Freeway acacia will tolerate low temperatures of –11.1° to –9.4°C (12°–15°F), alkaline and slightly saline soils, and does not seem to be choosy about soil types. In coastal areas it requires little or no supplemental irrigation, but does require regular irrigation in hot desert regions. Desert Carpet^TM seems to be disease and pest free.

Baccharis hybrid 'Starn' (P.P.A.F.) Thompson^TM

When Dr. Tommy Thompson and Dr. Chi Won Lee of the University of Arizona released Baccharis hybrid 'Centennial', it filled a great void in our plant palette. Their research has been carried on, and now the improved Thompson™ clone is available. Since Baccharis 'Centennial' is a female plant, it has two undesirable characteristics. First, it produces pappus, or white "fluff," which litters the landscape and reduces the esthetic appearance of the plants for a short period of time. Also, since 'Centennial' is a female plant, it can be pollinated by nearby male Baccharis sarothroides Gray (Desert broom), and seedlings often result. This is why you sometimes see stands of 'Centennial' with taller Baccharis plants growing up through them. The Thompson^TM clone is a male plant, eliminating these two negative characteristics. Also, Thompson^TM was selected from the next generation after 'Centennial', and has 25% more Baccharis sarothroides for heat and disease resistance. The growth habits and uses of these two clones are essentially the same: both grow to about 0.9 m (3 feet) tall by 1.2–1.5 m (4-5) feet wide, are evergreen with bright green foliage and inconspicuous flowers, and provide a low-maintenance, long-lived alternative for difficult locations.

Cercidium species 'Desert Museum'

This hybrid palo verde is a three-way cross between Parkinsonia aculeata L., Cercidium microphyllum (Torr.) Rose & I.M. Johnst., and Cercidium floridum Benth. ex Gray, and seems to combine the best qualities of all three plants. 'Desert Museum' grows very rapidly to 6.1 m (20 feet) tall and wide in 3 to 5 years, after which it needs little or no irrigation. It is completely thornless, and produces very little litter, with few seed pods. It has a sturdy, upright growth habit which requires very little pruning or staking. It blooms over a long period of time, with the heaviest bloom from about mid-March to May 1. It also tends to bloom again in June and August. The yellow flowers are larger than any of its three "parents." It does not reseed like the messy Parkinsonia aculeata!

Chilopsis linearis (Cav.) Sweet, Lucretia Hamilton^TM

Desert willow trees occur along washes throughout the southwestern US and northern Mexico. This small deciduous tree has narrow, light green leaves that give it a weeping appearance. In the summer, the tree is covered with fragrant, trumpet-shaped flowers. In the wild, the flower colors range from white to purple, although a pale pink to lavender flower color is the most common. The Lucretia Hamilton^TM clone was selected for its intense, deep pink to purple flower color, as well as its small stature. While many desert willow trees can grow to 7.6 m (25 feet) tall and wide, this clone seems to stay below 5.4–6.1 m (18-20 feet) tall and wide. After flowering, long narrow seed pods are produced. Plant Chilopsis linearis in full sun and well-drained soil, and in regions where temperatures do not drop below –17.8°C (0°F).

Chrysactinia mexicana Gray (Damianita)

This small, compact shrub grows to 0.6 m (2 feet) tall and wide, and bears a very strong resemblance to turpentine bush, with needle-like green leaves and yellow daisy-like flowers. However, damianita blooms from March to September, while turpentine bush blooms from September to November. Combining the two plants would be a great way to prolong the color display! Damianita has wonderful-smelling foliage, and would be a great selection for sensory gardens. Damianita is a very tough, durable plant, tolerating extreme heat and cold, down to –17.8°C (0°F). Plant in full sun, and almost any soil. If this plant starts to look woody, prune it back severely in the early spring. Damianita ranges from New Mexico to west Texas and northeastern Mexico, at elevations of 609–2134 m (2000–7000 feet).

Dalea capitata Sierra Gold^TM

This well-behaved ground cover grows to about 20 cm (8 inches) tall by 0.9 m (3 feet) wide. Because of its compact size, Sierra Gold^TM is a good selection for tight planting areas, such as small planters or medians. Its fine-textured, light green foliage has a fresh, lemony scent. Rabbits seem to avoid it! Yellow flowers carpet Sierra Gold^TM in the spring and the fall. This plant is hardy to at least –15°C (5°F), but it will be deciduous at –3.9°C (25°F). The one drawback to this plant is that the whiteflies seem to like it, so some insecticide applications will be necessary in heavily infested areas around Phoenix. Plant in full sun for best results. No soil amendments should be necessary. In hot desert regions this plant requires some supplemental irrigation from spring to fall. Although most dales native to Arizona and Mexico tend to rot out if overwatered, we have observed this plant thriving right next to turfgrass, where it receives heavy irrigation. More testing is needed to determine if it will tolerate coastal areas, or regions with high rainfall.

Dasylirion longissimum

This user-friendly accent plant is a great selection for high-traffic areas such as walkways and near entries. This grasslike plant does well in containers, and its symmetrical form provides a striking focal point. Its thin, stiff green leaves are completely unarmed, and have smooth edges. Eventually, its single trunk can grow to 1.8 m (6 feet), topped by a 1.5 m- (5-foot-) wide rounded head of leaves. The older, bottom leaves can be trimmed off to expose the trunk. Dasylirion longissimum is native to Mexico, and is hardy to about –8.3°C (17°F).

Euphorbia biglandulosa Desf. (Gopher Plant)

This evergreen perennial or subshrub has a very unusual form and appearance. Its arching stems angle out and up, and can reach a length of 0.6 m (2 feet). The plant grows to 0.9 m (3 feet) tall by 1.2 m (4 feet) across; with narrow, fleshy grey-green leaves. Broad clusters of chartreuse flowers occur at the tips of the arching stems, usually in the late winter and early spring. Flowers are followed by small brown seed pods that explode upon ripening. The stems usually die back after fruiting, leaving a small clump of grey-green foliage near the ground. Plant Euphorbia biglandulosa in full sun or light shade, in a well-draining soil. It is cold hardy to –15°C (5°F).

Hesperaloe parviflora (Torr.) J. Coult., 'Yellow' (Yellow yucca)

A clumping perennial with long, gray-green leaves, Hesperaloe parviflora grows slowly to form a grasslike clump 1.0–1.2 m (3–4 feet) tall and wide. From spring through fall, it produces 1.5 m- (5-foot-) tall flower spikes. Red-flowering plants have been a staple in southwestern landscapes for many years. This is simply a yellow-flowering selection. Use this tough accent plant in full sun. Since it also tolerates reflected heat, yellow yucca is a reliable plant to use along sidewalks, in parking lots, etc. Tolerant of temperature extremes, yellow yucca is cold-hardy to at least –17.8°C (0°F). Once established, it requires little or no irrigation. All in all, yellow yucca is one of the toughest and most maintenance-free plants.

Hymenoxys acaulis (Pursh) K. Parker (Angelita Daisy)

This perennial is native to the southwestern US, where it occurs most often at elevations from 1219–2134 m (4000–7000 feet), on dry rocky slopes and mesas. Angelita daisy bears a strong resemblance to Baileya multiradiata Harv. & A. Gray ex Torr. (desert marigold). However, the foliage is green rather than gray, and the flower is a deeper gold color. Forming rounded clumps to fifteen inches tall and wide, Hymenoxys acaulis is a wonderful plant to use as a border in front of larger shrubs. I f water is available, it will naturalize in the landscape. In Phoenix, this plant blooms all year, with especially heavy bloom in the spring and fall months. This prolonged bloom period results in many dried flower stalks, which can make the plants look scruffy. We recommend cutting off the old flower spikes occasionally to rejuvenate the plant and initiate new flower production. Angelita daisy seems to prefer well-drained soils and full sun. It is very cold hardy, heat tolerant, and drought tolerant.

Leucophyllum candidum I.M. Johnst. Thunder Cloud^TM

As with all of the other Leucophyllum species, this clone blooms when the humidity is high. The silver, pubescent foliage is a perfect foil for the masses of indigo flowers that appear in the summer and fall months. Thunder Cloud^TM was selected and trademarked by Benny Simpson of Texas A&M University. His clone is highly valued because of its small, dense growth habit. Unlike most of the larger Leucophyllum species, Thunder Cloud^TM remains reliably small, to three feet tall and wide. This plant is cold hardy to at least –12.2°C (10°F). Plant all of the Leucophyllum species in full sun and well-drained soil. Avoid overwatering.

Leucophyllum langmaniae Rio Bravo^TM

Trademarked by Mountain States Nursery, this clone has a nice, compact growth habit very similar to L. frutescens 'Compacta'. Rio Bravo^TM has become very popular because of its bright green foliage and rounded, dense form. It has lavender flowers and will eventually grow to 1.5 m (5 feet) tall and wide. Like the L. candidum species, it requires well-drained soils and full sun. It is hardy to –12.2°C (10°F).

Muhlenbergia capillaris (Lam.) Trin. Regal Mist^TM

We feel that this ornamental grass shows great promise for many different regions of the country. Native to humid southeastern Texas, this grass has adapted extremely well to the hot, dry conditions of deserts in Arizona and Nevada. In fact, it has performed incredibly well in Las Vegas, which is cursed with poor soils, high winds, high summer temperatures, and cold winters. Regal Mist^TM is also happy in heavy soils, with ample irrigation. In short, it has worked everywhere it has been tried, so far! It is hardy to at least –17.8°C (0°F). Regal Mist^TM has narrow, dark green, glossy leaves. It grows quickly to form a rounded clump to 0.9 m (3 feet) tall and wide. The flower spikes on this grass have attracted a lot of attention... they form misty masses of pink to purple flowers in October and November. We recommend cutting this plant back in early spring to cut off the dead flower spikes and any dormant foliage.

Penstemon species

There are so many wonderful Penstemon species to try in the garden, that is difficult to select just a few. Most of the penstemons are perennials with a basal rosette of foliage, which send up spikes of tubular flowers in the spring and early summer. They add incredible color to the landscape, and attract hummingbirds as well! Penstemons come in a wide range of colors, including blue, purple, pink, and red. After they finish blooming, allow the flower spikes to dry on the plant. Then cut off the spikes and sprinkle the seed in the garden to increase next year's mass of color. There are two new species to try: Penstemon triflorus Heller, which has short, 46 cm (18 inch) spikes of dark pink-purple flowers which occur along the stem in clusters of three; and Penstemon clevelandii Gray, native to southern and Baja California, with spikes of clear, bright pink flowers to 0.6–0.8 m (2–2.5 feet) tall.

Acacia nilotica (L.) Del

Uses

Some feel that the thorn bush of Exodus 3 was Acacia nilotica, the fire, the parasite Loranthus acaciae. Inner bark contains 18–23% tannin, used for tanning and dyeing leather black. Young pods produce a very pale tint in leather, notably goat hides (Kano leather). Pods were used by the ancient Egyptians. Young bark used as fiber, twigs esteemed for tooth brushes (chewsticks). Trees tapped for gum arabic. The gum arabic is still used in making candles, inks, matches, and paints (NAS, 1980). Tender pods and shoots used as vegetable, and used as forage for camels, sheep and goats, especially in Sudan, where it is said to improve milk from these animals. Seeds are a valuable cattle food. Roasted seed kernels, sometimes used for flavoring and when crushed provide the dye for black strings worn by Nankani women. Trees used in Sudan for afforestation of inundated areas. Sapwood is yellowish-white, heartwood reddish-brown, hard, heavy, durable, difficult to work, though taking a high polish. Because of its resins, it resists insects and water, and trees are harvested for the timber for boat-making, posts, buildings, water-pipes, well-planking, plows, cabinet-work, wheels, mallets and other implements. Wood yields excellent firewood and charcoal (Duke, 1981a). The aqueous extract of the fruit, rich in tannin (18–23%) has shown algicidal activity against Chroccoccus, Closteruim, Coelastrum, Cosmarium, Cyclotella, Euglena, Microcystis, Oscillatoria, Pediastrum, Rivularia, Spirogyra, and Spirulina (Ayoub, 1983).

Folk Medicine

Zulu take bark for cough, Chipi use root for tuberculosis. Masai are intoxicated by the bark and root decoction, said to impart courage, even aphrodisia, and the root is said to cure impotence. Astringent bark used for diarrhea, dysentery, and leprosy. Bruised leaves poulticed onto ulcers. According to Hartwell, the gum or bark is used for cancers and/or tumors (of ear, eye, or testicles) and indurations of liver and spleen, condylomas, and excess flesh. Said also to be used for cancer, colds, congestion, coughs, diarrhea, dysentery, fever, gallbladder, hemorrhage, hemorrhoids, leucorrhea, ophthalmia, sclerosis, smallpox, and tuberculosis. Bark, gum, leaves, and pods used medicinally in West Africa. Sap or bark, leaves, and young pods are strongly astringent due to tannin, and are chewed In Senegal as antiscorbutic; in Ethiopia as lactogogue. Bark decoction drunk for intestinal pains and diarrhea. Other preparations used for coughs, gargle, toothache, ophthalmia, and syphilitic ulcers. In Tonga, the root is used to treat tuberculosis. In Lebanon, the resin is mixed with orange-flower infusion for typhoid convalescence. Masai use the bark decoction as a nerve stimulant. In Italian Africa, the wood is used to treat smallpox. Egyptian Nubians believe that diabetics may eat unlimited carbohydrates as long as they also consume powdered pods (Duke, 1983a). Extracts are inhibitory to at least four species of pathogenic fungi (Umalkar et al, 1976).

Chemistry

Babul has been reported to contain l-arabinose, catechol, galactan, galactoaraban, galactose, N-acetyldjenkolic acid, N-acetyldjenkolic acid, sulphoxides pentosan, saponin, tannin. Seeds contain crude protein 18.6%, ether extract 4.4%, fiber 10.1%, nitrogen-free extract 61.2%, ash 5.7%, and silica 0.44%. Phosphorus 0.29% and calcium 0.90% of DM. When bullocks were given the seeds and bran (2:1) with dry pasture grass daily DM intakes were 1.82, 0.91, and 5.35 kg respectively. Total DM intake/100 kg bodyweight was 1.40 kg. The animals retained 20.8 g N and 7.4 g Ca daily but the P balance was slightly negative (Pande et al, 1981). Walker (1980) puts the CP content of the browse at 12.9%, the crude fiber at 15.2%

Description

Small tree, 2.5–14 m tall, quite variable in many aspects; bark of twigs not flaking off, gray to brown; branches spreading, with flat or rounded crown; bark thin, rough, fissured, deep red-brown; branchlets purple-brown, shortly or densely gray-pubescent, with lenticels; spines gray-pubescent, slightly recurved, up to 3 cm long; leaves often with 1–2 petiolar glands and other glands between all or only the uppermost pinnae; plnnae 2–11 (-17) pairs; leaflets 7–25 (-30) pairs, 1.5–7 mm long, 0.5–1.5 mm wide, glabrous or pubescent, apex obtuse; peduncles clustered at nodes of leafy and leafless branchlets; flowers bright yellow, in axillary heads 6–15 mm in diam.; involucel from near the base to about half-way up the peduncle, rarely somewhat higher; calyx 1–2 mm long, subglabrous to pubescent; corolla 2.5–3.5 mm long, glabrous or pubescent outside; pods especially variable, linear, indehiscent, 8–17 (-24) cm long, 1.3–2.2 cm broad, straight or curved, glabrous or gray-velvety, turgid, blackish, about 12-seeded; seeds deep blackish-brown, smooth, subcircular, compressed, areole 6–7 mm long, 4.5–5 mm wide. Fl. Oct.–Dec.; fr. Mar.–June (Duke, 1981a).

Germplasm

Acacia nilotica var. kraussiana (Benth.) Brenan is the most common form in east tropical Africa. Young branches more or less densely pubescent; pods not necklace-like, 1–1.8 cm wide, oblong, more or less pubescent all over at first with raised parts over seeds becoming glabrescent, shining and black when dry, margins shallowly crenate. Exhibits wide range of altitudinal and habitat requirements. Found in Botswana, Zambia, Rhodesia, Malawi, Tanzania, Angola, Mozambique, Transvaal, and Natal. A. nilotica var. tomentosa A. F. Hill (A. arabica var. tomentosa Benth.), has pods straight, constricted between seeds and densely tomentose; found in Senegal and northern Nigeria, to Sudan, Arabia and India. A. nilotica var. adansonii (Guill. et Perr.) Kuntze is a tree up to 17 m with dark reddish-brown bark deeply fissured, tomentose, reddish-brown twigs and gray fruits; commonest variety in West Africa, from Senegal to Nigeria and widespread in northern parts of Tropical Africa. Assigned to the African Center of Diversity, babul or cvs thereof is reported to exhibit tolerance to clay, drought, heat, heavy soil, high pH, poor soils, salt, savanna, and waterlogging. (2n=52.)

Distribution

Native from Egypt south to Mozambique and Natal; apparently introduced to Zanzibar, Pemba, and India; Arabia. Considered a serious weed in South Africa.

Ecology

Woodlands of various sorts, wooded grasslands, scrub and thickets. Thrives in dry areas, but endures floods. Grows 10–1,340 m altitude, in a wide range of conditions. Grows on a wide variety of soils, seemingly thriving on alluvial soils, black cotton soils, heavy clay soils, as well as even poorer soils (NAS, 1980). Ranging from Subtropical Desert to Subtropical Dry through Tropical Desert to Tropical Dry Forest Life Zones, babul is reported to tolerate annual precipitation of 3.8–22.8 dm (mean of 12 cases = 12.0 dm), annual mean temperature of 18.7–27.8°C (mean of 12 cases = 24.1°C), and pH of 5.0–8.0 (mean of 10 cases = 6.9) (Duke, 1981a).

Cultivation

Trees propagated in forest by seeds. Direct seeding is the common practice. Stored seed may require scarification. Young seedlings are said to "require full sun and frequent weeding" (NAS, 1980a).

Harvesting

Although there are other sources of gum arabic, trees are still tapped for the gum by removing a bit of bark 5–7.5 cm wide and bruising the surrounding bark with mallet or hammer. The resulting reddish gum, almost completely soluble and tasteless, is formed into balls. Though used in commerce to some extent, it is inferior to other forms of gum arabic, with which it is sometimes mixed.

Yields and Economics

Various products of the tree are used locally in tropical Africa, but none enter international markets. Trees usually add 2–3 cm in diameter each year (NAS, 1980a).

Energy

Extensively used, e.g. in India, for firewood and charcoal, this species has been used in locomotives and steamships as well as industry balers. It is cultivated for industrial fuel in the Sudan. The calorific value of the sapwood is 4,800 kcal/kg of the heartwood 4,950. The species does nodulate and fix nitrogen.

Biotic Factors

Wood borers may afflict the stems and bruchids may afflict the seeds. Following fungi have been reported on this plant: Ctyospora acaciae, Diatryphe acaciae, Diplodia acaciae, Fomes badius, F. endotheius, F. fastuosus, F. rimosus, Fusicoccum indicum, Phyllactinia acaciae, Ravenelia acaciae-arabicae, Septogloeum acaciae, Septoria mortolensis, Sphaerostilbe acaciae. Trees are also parasitized by Dendrophthoe falcata and Loranthus globiferus var. verrucosus (Duke, 1981). In a survey for phytophagous insects on Acacia nilotica, 43 species were recorded in Pakistan, of these, 16 appeared stenophagous. The more promising for biological control of the tree were: Anarsia sp. cf. acaciae, Pseudosterrha paulula, Azanus ubaldus, and Ceutholopha isidis feeding on flowers; Bruchidius sahlbergi and Sulcobruchus sp. damaging seeds; Ascalenia callynella, Gisilia stereodoxa and an unidentified gracillariid boring shoots; and Cydia sp. making stem galls (Mohyuddin, 1981).

Yields and Economics

Various products of the tree are used locally in tropical Africa, blit none enter international markets. Trees usually add 2–3 cm in diameter each year (NAS, 1980).

References

• Ayoub, S.M.H. 1983. Algicidal properties of Acacia nilotica. Fitoterapia 53(5–6):175–8.
  
• Duke, 1981.
  
• Duke, J.A. 1981a. Handbook of legumes of world economic importance. Plenum Press. NewYork.
  
• Duke, J.A. 1983a. Medicinal plants of the Bible. Trado-Medic Books, Owerri, NY.
  
• Mohyuddin, A.I. 1981. Phytophages associated with Acacia nilotica in Pakistan and possibilities of their introduction into Australia. p. 161–166. Proceedings of the 5th International Symposium on Biological Control of Weeds. Australia Commonwealth Scientific and Industrial Research Organization.
  
• N.A.S. 1980a. Firewood crops. Shrub and tree species for energy production. National Academy of Sciences, Washington, DC.
  
• Pande, M.B., Talpada, P.M., Patel, J.S., and Shukla, P.C. 1981. Note on the nutritive value of babul (Acacia nilotica L.) seeds (extracted). In: Indian J. Anim. Sci. 51(1):107–108.
  
• Umalkar, C.V., Begum, S., Nehemiah, K.M.A. 1976. Inhibitory effect of Acacia nilotica extracts on pectolytic enzyme production by some pathogenic fungi. Indian Phytopath.: publ. 1977, 29(4):469–470.
  
• Walker, B.H. 1980. A review of browse and its role in livestock production in southern Africa. p. 7–24. In: LeHouerou, H.N. (ed.), Browse in Africa. International Livestock Centre for Africa. Addis Ababa, Ethiopia.