This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Deciduous trees or shrubs, often spiny, with imparipinnate leaves and axillary racemes of white, rose, or purple flowers. Standard large and broad, naked within; wings oblong-falcate, free; keel incurved, obtuse. Vexillary stamen connected with the others at the middle. Pod linear, the upper suture narrowly winged, valves thin. About five or six species, all North American. Named after M. Robin, a French botanist.
1. R. hispida (fig. 71). Rose Acacia. - A small shrub having the young branches and petioles densely clothed with bristles. Leaflets oblong or oval, entire, midrib terminating in a fine bristle. Flowers larger than in the following, rose or pink. A variable plant with regard to the size of the leaves and colour of the flowers, and in one variety the characteristic bristly hairs are wholly wanting. A native of North America.
2. R. Pseud-acacia. Thorn or False Acacia. - A tall rapid-growing tree with long slender smooth shoots and the stipules usually transformed into strong rigid sharp spines. The ordi- nary form has from 9 to 21 oblong or oval leaflets, and white odoriferous flowers slightly tinged with pink. But there are about a hundred varieties, and the extreme forms are widely different in aspect. In R. Ps. inermis the characteristic thorns are wanting, and the leaflets are narrow, oblong, and glaucous beneath; Decaisneana has bright rosy flowers; monophylla has the leaf reduced to one large leaflet; pendula is of drooping habit; and crispa, monstrosa, and dissecta differ in the foliage. Besides the above there is a yellow-flowered variety, and others- in which the leaflets are much smaller or larger than in the so-called typical form. Then there is the variety tortuosa with zigzag branches, and varieties variegated with white or yellow.
Fig. 71. Robinia hispida. (1/6 nat. size.)
3. R. viscdsa, syn. R. glutinosa. - A small tree. Young shoots clammy. Flowers rose-pink, nearly scentless, crowded in short racemes; pod clothed with glandular hairs. Possibly one of the many variations of the Thorn Acacia. North America.