Black locust

Robinia pseudoacacia, commonly known in its native territory as black locust, is a medium-sized hardwood deciduous tree, belonging to the tribe Robinieae of the legume family Fabaceae. It is native to a few small areas of the United States, but it has been widely planted and naturalized elsewhere in temperate North America, Europe, Southern Africa and Asia and is considered an invasive species in some areas, such as the temperate east coast of Australia where the cultivar “Frisia” (Golden Robinia) was widely planted as a street tree before being classed as a weed. Another common name is false acacia, a literal translation of the specific name (pseudo [Greek ψευδο-] meaning fake or false and acacia referring to the genus of plants with the same name).

Black locust – Description

Since buds are formed in the axils of leaves, their distribution on the stem is the same as that of leaves. There are alternate, opposite, and whorled buds, as well as the terminal bud at the tip of the stem. In many plants buds appear in unexpected places: these are known as adventitious buds.

Often it is possible to find a bud in a remarkable series of gradations of bud scales. In the buckeye, for example, one may see a complete gradation from the small brown outer scale through larger scales which on unfolding become somewhat green to the inner scales of the bud, which are remarkably leaf-like. Such a series suggests that the scales of the bud are in truth leaves, modified to protect the more delicate parts of the plant during unfavorable periods.

The dark blue-green leaves are lighter on the underside,[citation needed] and are compound, meaning that each leaf contains many smaller leaflike structures called leaflets, which are roughly paired on either side of the stem that runs through the leaf (rachis). There is typically one leaflet at the tip of the leaf (odd pinnate), and the leaves are alternately arranged on the stem. Each leaf is 15–36 cm (6–14 in) long and contains 9–19 leaflets, each being 2.5–5.1 cm (1–2 in) long, and .65–1.9 cm (1⁄4–3⁄4 in) wide. The leaflets are rounded or slightly indented at the tip and typically rounded at the base. The leaves come out of the bud folded in half, yellow green, covered with silvery down which soon disappears. Each leaflet initially has a minute stipel, which quickly falls, and is connected to the (rachis) by a short stem or petiolule. The leaves are attached to the branch with slender hairy petioles which are grooved and swollen at the base. The stipules are linear, downy, membranous at first and occasionally develop into prickles. The leaves appear relatively late in spring, and turn a clear pale yellow in autumn. The leaflets fold together in wet weather and at night (nyctinasty), as some change of position at night is a habit of the entire leguminous family.

Young trees are often spiny, especially on root suckers and branches near the ground; mature trees often lack spines. R. pseudoacacia is quite variable in the number of spines present, as some trees are densely prickly and other trees have no prickles at all. The spines typically remain on the tree until the young thin bark to which they are attached is replaced by the thicker mature bark. They develop from stipules[10] (small leaf-like structures that grow at the base of leaves), and since stipules are paired at the base of leaves, the spines will be paired at the bases of leaves. They range from .65–2 cm (1⁄4–3⁄4 in) in length and are somewhat triangular with a flared base and sharp point. Their color is of a dark purple and they adhere only to the bark.

The winter buds are minute, naked (having no scales covering them), three or four together, protected in a depression by a scale-like covering lined on the inner surface with a thick coat of tomentum and opening in early spring. When the buds are forming they are covered by the swollen base of the petiole.[citation needed] The large flowers open in May or June for 7–10 days, after the leaves have developed. They are arranged in loose drooping clumps (racemes) which are typically 10–20 cm (4–8 in) long. The flowers themselves are cream-white (rarely pink or purple) with a pale yellow blotch in the center and imperfectly papilionaceous in shape. They are about 2.5 cm (1 in) wide, very fragrant, and produce large amounts of nectar. Each flower is perfect, having both stamens and a pistil (male and female parts). There are 10 stamens enclosed within the petals; these are fused together in a diadelphous configuration, where the filaments of 9 are all joined to form a tube and one stamen is separate and above the joined stamens. The single ovary is superior and contains several ovules. Below each flower is a calyx which looks like leafy tube between the flower and the stem. It is made from fused sepals and is dark green and may be blotched with red. The pedicels (stems which connect the flower to the branch) are slender, 1.3 cm (1⁄2 in), dark red or reddish green.

The fruit is a typical legume fruit, being a flat and smooth pea-like pod 5.1–10.2 cm (2–4 in) long and 1.3 cm (1⁄2 in) broad. The fruit usually contains 4–8 seeds. The seeds are dark orange brown with irregular markings. They ripen late in autumn and hang on the branches until early spring. There are typically 25,500 seeds per pound. Cotyledons are oval in shape and fleshy.

Source:  WIKIPEDIA