Of the forty or so species of Caesalpinia known, two or three can be grown in the milder parts of the kingdom, but even as far south as Kew they need some shelter in the open air. Among hardy trees and shrubs they are most nearly allied to Gymnocladus and Gleditsia. The flowers are very dissimilar to those of the commoner pea-flowered type of Leguminosae, the petals being almost equal in size and shape. The other essential features are the tubular, five-toothed calyx, the ten free stamens, and the thick, compressed, leathery pod. Named after Andreas Caesalpini, an Italian botanist, 1519-1603.