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A deciduous, round-headed tree up to 20 ft high, with a trunk 8 to 10 in. in diameter; young shoots slightly downy. Leaves pinnate, 6 to 9 in. long, with thirteen to nineteen leaflets which are oval, tapering about equally towards both ends, shortly stalked, 1 to 11⁄2 in. long, about 1⁄2 in. wide, slightly downy beneath when young. Flowers in slender downy racemes 3 to 6 in. long, produced in June in the leaf-axils of the new growths, white tinged with rose, 1⁄2 in. or rather more long. Calyx downy, bell-shaped, with broad, shallow triangular teeth. Pods 11⁄2 to 3 in. long, black, downy, persisting long on the tree. By the constrictions of the pod, each seed has its own oval or globose compartment, the inner wall of which is fleshy; the pod rather suggests a string of three or four beads.
Native of Texas and Arkansas, often on limestone hills; discovered in Texas in 1821; introduced to cultivation in 1890. Sargent observes that a domestic ink is sometimes made from the resinous exudations of the black fruits. In leaf this sophora resembles S. japonica, but that species is very distinct in having terminal, autumnal flower panicles. S. affinis would probably succeed best on the south or east coast, where it should make a pleasing small tree. After being probably extinct in British gardens it is again available in commerce (1978).
This uncommon American species is represented at Kew and in the Hillier Arboretum, Ampfield, Hants.