Amorpha L. (1753), in the family Leguminosae subfamily Papilionoideae, contains around 15 species in North America. Description Shrubs to 3m. The leaves are alternate, deciduous, pinnate, with 11–51 leaflets, with a terminal leaflet. The flowers are very small and numerous, often scented, in long, upright spikes, not pea-like, usually purplish or bluish. Sepals 5, unequal, joined at the base to form a tubular, toothed calyx. Petals 1, only the standard, which encloses lower parts of the stamens, style, and ovary. Stamens 10, with their filaments all joined at the base. Ovary superior, with 1 carpel containing 1 or 2 ovules; style 1, long and slender. Pollination is presumed to be by insects. The pods are small with 1 or 2 seeds. Key Recognition Features The upright or spreading spikes of minute, dull-purplish or bluish flowers. Evolution and Relationships The flowers are very reduced, but produced in huge numbers. In the related, vetch-like genus Dalea L., which is common on the American prairies, the small flowers are in clover-like heads (Trifolium L.), and have wings and keel mostly longer than the standard. Ecology and Geography In sandy woods, especially by streams, and on river banks and floodplains in North America, extending into Mexico. Comment The genus is unusual in its very reduced flowers, and is sometimes cultivated in collections of shrubs. |
