Acacia laevis Hort. Ex Steud.

Gleditsia triacanthos attains a normal height of 15-25 (50) m and 0.5-1 (max. 1.8) m diameter. Trees have a short bole and open, narrow or spreading crown, bark reddish-brown to black, scaly, ridged, often covered in clusters of large, branched thorns. It has a strong taproot and a profusely branched root system. Leaves deciduous, alternate, singly or doubly pinnately compound. Those singly compound form early on dwarf shoots or toward the base of the long shoots; bear 14-30 leaflets (no terminal leaflet) on a central stalk 15-20 cm long; preformed in buds. Those doubly compound bear 4-7 pairs of branches, each resembling a singly compound leaf; neoformed during the growing season. Leaflets 25-40 mm long, widest near the base; tip rounded, often with a small point; sometimes minutely toothed. Flowers greenish-white, regular, small, about 5 mm across. The male and female flowers on the same tree, often on separate branches. Perfect flowers may also be present. Pollen flowers in many-flowered clusters (racemes) 5-7 cm long. Seed flowers in few-flowered clusters 7-9 cm long. Fruit 15-40 cm long pods, flat, curved, twisted, brownish; husk leathery; falling in winter without opening. Seeds beanlike; with a hard, impermeable seed coat; 0.5-1.5 cm long, dark brown, smooth. The generic name, sometimes spelt Gleditschia, commemorates the German botanist Johan Gottlieb Gleditsch (1714-1786), professor and director of the Berlin Botanic Garden. The specific name ‘tricanthos’ means 3-thorned; from the Greek ‘treis’ (three) and ‘akantha’ (a spine).

Grafted seedlings begin to bear pods after 3 years and within 8 years will produce a dry weight of pods of 20-75 kg/tree. In the southern United States, the bee-pollinated flowers appear from early May and to late June in the north. Mature pods begin to drop by mid-September and continue throughout the winter. Seeds ripen from mid- September to late October in the United States.

Best growth is found on deep soils (pH 6-8) in moist, alluvial floodplains although it also grows in saline soils. It generally grows poorly on gravelly or heavy clay soils and often fails on shallow soils.

Within the natural range, a large amount of variation exists in both climate and soil conditions. G. triacanthos occurs naturally in humid and subhumid climate regions; it grows naturally to 760 m but has been planted from sea level to 1500 m in temperate latitudes and will grow above 2500 m in subtropical highlands. It is shade intolerant and will only become established in open spaces. G. triacanthos is resistant to both drought and salinity.

G. triacanthos was cultivated by American colonists sometime in the late 17th century. The first account of it, drawn from the cultivated tree, was published in 1700 by Plukenet in his Amalthum Botanicum, with a brief description and illustration. Well-known as an ornamental street tree, G. triacanthos was widely advocated as a livestock feed early in the 20th century. Silvopastoral cultivar development began in the 1930s at the Tennessee Valley Authority in the United States of America. It was known in France in the early 18th century and spread shortly afterwards to other European countries. The tree was 1st cultivated in Europe by Bishop Compton in his garden at Fulham near London in about 1700. Since its introduction into cultivation, in both America and Europe, G. triacanthos has been extensively planted in most countries as an ornamental tree. It does well in such wide-ranging areas as the steppes of southern Russia and Tunisia and is reported also in cultivation in South Africa and South America.

Mature pods can be collected after they drop off, or by hitting branches to jar the pods loose, or by clipping pods from the branches. Successful germination requires seed scarification by immersion in concentrated sulphuric acid (60-120 minutes followed by thorough rinsing), hot water (82 deg. C), or by mechanical means. To prepare pods for mechanical seed extraction, place them in a convection or seed-drying oven for at least 2 hours at 35 deg. C. Germination of sound seed should be in the range of 75-95%. Seeds should be sown 0.5-1.5 cm deep and, if they are properly scarified, complete germination will occur within 21 days. Dormant, nursery-grown seedlings can be stored, bare rooted, at about 0 deg. C for several weeks before planting out. For successful propagation of G. triacanthos, chip budding with green wood works best. Dormant scionwood results in a low percentage of successful grafts; 1-year-old seedlings (or budded/grafted material) can be out-planted the following spring. Due to large variation in pod production from different parent trees, and the presence of both male and female trees, only grafted seedlings are recommended for planting to secure consistently high production at an early age.

Male trees (about 10%) must be included in or adjacent to fodder orchards to ensure pollination of female trees. When established in working pastures, young trees need protection with plastic tree shelters or electric fencing. Appropriately managed, average annual pod production of 40 kg/tree appears feasible. Planting 75 trees/ha (excluding male trees) would yield 3000 kg/ha, sufficient to provide 100 sheep a 1.5-kg ration of pods for 20 days. The tree coppices vigorously when cut. Typical of many caesalpinioid genera, G. triacanthos does not nodulate and lacks the ability for symbiotic fixation of atmospheric nitrogen.

Grazing animals may damage young plants, while other animals and birds may eat the pods. The mimosa webworm, Homadaula anisocentra, is a serious defoliant and heavy infestations of spider mites (Eotetranychus multidigituli) occur during dry weather and can also defoliate a tree. Bruchid weevils (Amblycerus robiniae) are sometimes found in the seeds.

After harvest, pods should be stored at 0 deg. C to prevent fermentation. If bruchid seed weevils (Amblycerus robiniae) are present in the pods, it will prevent them from spreading within the pods. Seed storage behaviour is orthodox. A few seeds germinated after 50 years in storage at 4% mc and ambient temperature; viability was maintained for several years in hermetic air-dry storage at 0-8 deg. C. Seed yield averages 5200 seeds/kg (3300-14 300, depending on the seed source) with high purity and soundness.

Erosion control: Because it can be applied in erosion control, G. triacanthos is being tested in many temperate, Mediterranean and highland tropic regions of the world. Shade or shelter: G. triacanthos is hardy and drought tolerant; it can be grown in windbreaks with the added benefit of pod production. Ornamental: Its readiness to grow from seed, rapid growth, easy culture and extreme hardiness are among the commendable characters that make this tree popular for planting in gardens, parks or along highways. It has been widely planted as a replacement for American elm in North America and Canada with over 50 recognized cultivars. Budding can produce thornless trees with scionwood taken from the upper branches of selected cultivars. Thornless seedlings can be selected at a very early age (within 10 weeks of germination) for use as ornamental cultivars. Intercropping: Widely spaced overstorey fodder trees (fodder orchard) can be planted for on-farm silvopastoral systems and should be compatible with a variety of forage, grain, vegetable, woody perennials or animals in the understorey.

Food: Seeds have been roasted and used as a coffee substitute. Fodder: G. triacanthos leaves are an excellent source of fodder, contain 20% crude protein, low lignin and ensile well. Coppice regrowth retains high protein and low lignin levels. It has used as fodder in Australia and elsewhere. However, limited studies indicate very low biomass yield response when planted from seed and harvested with a forage harvester during the 1st year’s growth, or when 1-year-old seedlings were coppiced after a full year for establishment and growth. Sheep are able to digest the majority of seeds within the pods. However, for complete utilization by sheep, cattle, horses or swine, pods and seeds must be machine processed. Apiculture: Flowers are very attractive to bees, which make honey from the nectar. Fuel: The specific gravity of the wood is 0.60 green, 0.67 oven-dry, and it is considered an excellent source of fuelwood. Medicine: In Lesotho, fruit pulp is used for lung diseases. Powdered seed is used as snuff for head colds. Reported to be anodyne, mydriatic, narcotic, and experimentally oxytocic, G. triacanthos pods are a folk remedy for dyspepsia and measles, colds and fevers among the Indians of the USA; Delaware Indians used the bark for blood disorders and coughs. The bark tea treats whooping cough. Timber: The wood is strong, hard and durable, resistant to shock, and reddish-brown with attractive figuring; it is used locally for fence posts, pallets, crating, general construction, railroad ties and by woodworkers for making guitars. Gum or resin: The gum from the seeds has been suggested as an emulsifying substitute for acacia gum and tragacanth. Alcohol: A potable or energy alcohol can be made by fermenting the pulp. Poison: Triacanthine from the leaves is highly toxic (LD50 about 35 mg/kg) and of questionable oncostatic activity.