Gleditsia sinensis Seeds | Chinese Honey Locust
LATIN NAME: Gleditsia sinensis
COMMON NAME: Chinese Honey Locust
Plant Profile
Split a ripe pod and the inside is not the sweet pulp of the American honey locust but a leathery, slimy wall rich in saponin. Rubbed in water it foams, and the pods were used as a washing agent across much of China long before soap was a shop commodity. The pods are collected in late autumn and dried whole, and the lather is strongest from the inner face of the pod wall.
Pods hang flat, slightly curved, dark brown and dusted with a pale bloom, and they twist as they dry before the two valves separate. A pod that rattles when shaken is ready for seed extraction; a green pod cut too early gives seed with a soft coat that stores badly.
The flowers are small, pale yellow-green, and arranged in short racemes on the wood of the previous season; there are no petals worth the name, and the sexual parts are carried on separate flowers that are only imperfectly divided between the sexes on the same tree. Pollination is left to wind and to small insects, and the ornament of the tree is the pod, not the bloom. The seed itself is a hard, glossy, flattened oval with a stony testa and a small pleurogram, set flat in the pod cavity in a single row.
The tree has been planted around Chinese villages and temple grounds for centuries for its pods rather than its timber, and old specimens are often hollow and storm-broken yet still fruiting. In Europe and North America the related genus and the American species have been the street-tree favourites, while this Asian species remains mainly a crop plant. The wood is hard, coarse and durable enough for tool handles and cart parts, and it takes a good polish, but the thorny trunk limits its use in plantation forestry.
Science & Biotechnology
The surfactants belong to the triterpenoid saponins, built on an echinocystic acid skeleton with sugar chains attached, and the series is named after the genus as the gleditsiosides. The seed kernel carries a different and more toxic set of sapogenins, which is why the two fractions are never treated as one material in the laboratory.
The foliage is twice compound — a rachis carrying pinnae, each pinna carrying many small oval leaflets — and the leaflets fold slightly in bright heat, so the tree casts a light, moving shade rather than a dense block of shadow. Some shoots carry simple leaves and others carry the compound ones on the same tree, a heterophyllous habit that is easy to spot on a young plant. Trunks and branches are grey-brown and rather smooth until the thorny bosses break the outline.
Uses & Benefits
Young trees look lightly armed and old ones look like a fence. The thorns of the Chinese honey locust are not the simple spines of a rose; they are stout, hard, branching structures that rise from the wood of the trunk itself, sometimes dividing into three or four points, and on an old tree they can reach the length of a hand. Because they are woody branch systems rather than a surface armament, they are not shed, and a mature specimen wears them for life.
Growing from Seed
Because the thorns make the tree awkward in the nursery and in the street, growers have selected thornless forms and propagated them by grafting onto seedling rootstock; a thornless scion is worth nothing if the stock throws suckers, so the union is kept high and the rootstock shoots removed. Seedling families segregate widely for thorn length and pod size, and a seedlot collected from an orchard is rarely uniform.
Clonal propagation has been attempted through axillary shoot multiplication on seedling material and through somatic embryogenesis from immature cotyledons, using a cytokinin-rich medium to force buds from the cotyledonary node. The approach matters for this species because selected mother trees are old, grafted and hard to multiply by cuttings, and because a uniform thornless line would sell well as a street tree. Regenerated plants often need a hardening stage in a mist tunnel before they tolerate open air.
The seed coat is almost impermeable and a proportion of any lot will sit dormant for a long time if it is left alone. Chipping or nicking the coat on the side away from the embryo, or pouring water just off the boil over the seed and letting it cool overnight, opens the way for water to enter. Direct sowing into deep containers gives the long taproot room; a seedling held too long in a shallow tray develops a bent root that never straightens.
Our Take
Give it sun, deep ground and room; the thorns make pruning a job for leather gloves and long loppers, and nothing else about the tree is demanding. Collected pods keep their lather for several seasons if they are stored dry and off the ground. For related legume trees with very different habits, see honey locust, the American species with sweet pod pulp, and black locust, a nitrogen-fixing pioneer. Japanese scholar tree makes the same fine pinnate shade without a single thorn.
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