Robinia pseudoacacia

Robinia Winter

figure 85

Winter twig of robinia [life size) showing typical angular growth. Single bud (X5) near centre of large leaf scar, which almost hides it Typical paired spines.

The robinia is named after Jean Robin, a French botanist who first described it in 1601, shortly before it was introduced to Europe from its home in the south-eastern states of North America. It is also called the 'locust tree' because early setders thought it might be the tree that nourished John the Baptist in the wilderness, though its seeds are not good to eat. Yet another name is 'acacia' or 'false acacia', again from a false identification with a Biblical thorny tree, because it carries little spines, always in pairs, at the base of each leaf.

figure 85

Winter twig of robinia [life size) showing typical angular growth. Single bud (X5) near centre of large leaf scar, which almost hides it Typical paired spines.

Golden Robinia Winter

FIGURE S6

Flowering shoot of robinia in June, showing pinnately compound leaves and hanging racemes of white Sweet pea-shaped blossoms (x'). Single flower (X2) with calyx of sepals, large 'standard' petal at top, 'wings' at sides, and 'keel' below.

Robinia is easy to identify, since no other tree bears such paired spines; the winter buds beside them are virtually invisible, being small, scale-less and hidden by the base of the fallen leaf stalk. The scar of the old leaf stalk is large. The leaves are a little like those of an ash tree, but are alternately set (not opposite) and have more rounded leaflets. The pale grey bark on old stems becomes thick and is patterned with irregular ribs.

Flowers, which are carried in profusion on the crowns of tail trees in June, are white and hang in long drooping racemes. Each separate blossom resembles a Sweet pea flower, for robinia belongs to the same family, the Leguminosae, It has five green sepals and five white petals set in a typical pattern - a large 'standard' at the back, two 'wings' at the sides, and two petals at the front folded together to form a 'keel.' This arrangement helps to guide a visiting bee, in search of nectar, over the five stamens that dust it with yellow pollen, and close to the one-chambered pistil at the centre. Seed pods, which ripen by October, are greyish, hard, swollen and bent, and hold several hard black seeds.

The wood of robinia is golden yellow in colour, with a paler sapwood fringe. It is hard, strong and naturally durable, and the American settlers made great use of it for fencing, tool handles, cart shafts and other exacting purposes. Unfortunately the trunk is nearly always twisted and fluted, and now that sawmills have succeeded hand tools for working up timber, it is scarcely ever used. Robinia is grown simply as an ornamental tree in cities, parks and large gardens. It is unsuitable for smaller ones since it drops a varied titter of spent blossom, faded leaves and seed pods, and is apt to send up strong sucker shoots from its roots. These roots carry the nodules, typical for the Sweet pea family, which hold bacteria that enable the plant to 'fix' the nitrogen of the air; this enables robinia to thrive on poor soils, so it is sometimes used to cover slag heaps.

Seeds Peas Pod

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