Mimosa esculenta Sesse & Moc.

Leucaena esculenta is a deciduous, small to medium-sized tree 10-15 m tall, 20-70 cm bole diameter, typically multi-stemmed and branchy when young, older trees with a short clear bole to 5 m, heavy spreading branches and an open spreading rounded crown. Bark thick, corky, pale silvery grey, with a metallic sheen like galvanized zinc, smooth, becoming horizontally gnarled; slash bright green then orange-red, shoots angular with 5-6 longitudinal corky ridges. Leaves bipinnate, 30-40 pairs of pinnae, leaflets 3.5-6.6 mm long by 0.9-1 mm wide, 60-75 pairs per pinna, asymmetric, linear, acute or subacute, glabrous. Petiole gland large, maroon-red, sessile, elliptic, shallowly concave 5.5-8 by 3-4 mm. Flower head 25-28 mm in diameter, 150-170 flowers per head, in groups of 2-7 at nodes on often one-branched terminal determinate shoots with complete or partial suppression of leaf development, flowers white. Pods 15-25 cm long, 23-26 mm wide, 1-2 per flower head, oblong to oblong linear, flat, (few) 15-20 seeded, glossy reddish maroon unripe, turning mid orange-brown when ripe, glabrous, opening along both sides. Seed 9-11 mm long, 7-9 mm wide, circular to ovoid, aligned transversely in pods. The specific epithet means edible.

The main flowering period is between October and November, while fruiting follows between February and March. Trees are deciduous, losing most or all of the leaves during the dry season from January to April in the species natural range.

L. esculenta occurs mainly on soils derived from calcareous parent material, unstratified regosols, shallow and rocky soils which are free draining.

L. esculenta forms a canopy tree in mid-elevation seasonally dry deciduous tropical forest and at higher elevations in oak, oak-juniper and juniper forest. It can withstand up to seven months dry season and occasional light frost but it does not thrive above 2 000 m. Rainfall in its natural range is highly seasonal and the dry season lasts up to 7 months. Soils are mainly calcareous.

This species has a long and diverse history of human use, cultivation and incipient indigenous domestication stretching back over several millennia. It is widely cultivated throughout the highlands of central Mexico for its edible pods. It has also been introduced to Senegal where it has been found to hybridize readily with L. leucocephala ssp. glabrata where the two are brought together in cultivation. Therefore, its present day distribution is more extensive than its true natural distribution, which is difficult to define precisely. It is likely to be introduced, possibly in pre-Columbian times in other parts of Mexico. It has been more widely introduced in trials in the 1990s in other countries.

The seeds are large, relatively soft and do not require pretreatment. They can be sown directly and will germinate rapidly giving a rapid initial growth. Results of experiments showed that untreated fresh seed gives up to 79 % of the expected germination with manual scarification.

There are 3 forms of management of L. esculenta in its native range: cultivation, selective retention or tolerance of particular individuals in disturbed areas and gathering from purely wild populations. The tree is tolerant of annual lopping and is adaptable to a range of management regimes in agroforestry. Trees are heavily lopped each year during the dry season when pods are produced and resprout vigorously with the onset of rains. In addition, trees are frequently cut to produce livestock fodder. The tree’s rapid growth, moderate drought and cold tolerance, and high resistance to the psyllid attack indicate that L. esculenta has considerable untapped potential for wider planting.

The seeds of L. esculenta are attacked by several bruchid species in the genus Acanthoscelides including A. macrophthalmus, A. mankinsii, A. boneii and A. leucaenicola.

There are around 8 700 seeds/kg. Seeds tend to harden with storage. Seed production, although abundant in its native range, can be very sparse under some climatic conditions, such as Hawaii and this may have limited its wider spread.

Shade or shelter: It is used as a shade tree especially for coffee. Nitrogen fixing: The tree is nitrogen fixing. Soil improver: Lopped leaves and twigs can be applied as green manure. Ornamental: Hybrids such as L. retusa x L. esculenta make attractive home ornamentals. Boundary or barrier or support: The tree is planted at field boundaries or as living fences. Intercropping: The species is widely incorporated in cropping systems with annual or fruit crops. Other services: L. esculenta is highly resistant to the psyllid (Heteropsylla cubana), and it has been used in breeding programmes.

Food: In the trees native region, the pods, seeds, and young leaves are gathered from wild populations. The immature pods, leaf and flower buds are edible. They are the traditional greens of the indigenous people of Mexico. They are gathered from June to September. Galls frequently develop on leaves and pods, these are consumed raw, roasted or boiled. Immature seeds are the products most consumed and are either eaten raw, roasted, milled and added to traditional sauces, or cooked in stews. Seeds are gathered in from November to February, when they are still immature. They may be consumed fresh or ground into a paste and sun dried for long term storage. They are also stored after being dried and salted. Fodder: In Mexico, trees are lopped for livestock fodder. Both leaves and unripe pods are consumed. However, low edible fraction, in vitro dry matter digestibility and high-condensed tannin levels limit its importance. Fuel: The tree provides high quality fuelwood. Timber: The wood of L. esculenta has an average density of (0.7), with slow early formation of heartwood. It is rarely used in Mexico because trees are protected for pod production. Non-seedy or seedless clones are attractive options for most of leucaena's wood uses, including fuelwood, pulpwood, roundwood, charcoal, parquet, and craftwood. Gum or resin: Analysis of several leucaena gums has revealed that they have the closest match to gum arabic of any gums tested from a hundred or so tropical trees. Although toxicity and related studies are needed, leucaena gum may have potential for use as a substitute for gum arabic. L. leucocephala x L. esculenta hybrid trees exuded gum copiously. Nine hybrid trees of this pedigree were grown at Waimanalo, Hawaii for four years during which approximately a third failed to produce gum, another third exuded gums sporadically and another third exuded gums heavily. These high gum yielders exceeded the mean annual per-tree gum production (250 g/tree) of gum arabic by Acacia senegal. Gum production appeared as balls or drippings from mature bark, and was heaviest in the dry season. Hybrids of this type are seedless, have good vigor and psyllid resistance, and could prove promising for gum production.