Revision of the United States Species of Neptunia (Leguminosae)

The genus Neptunia was first described by Loureiro in Flora Cochinchinensis 2: 653, 1790. He based it upon an aquatic species, N. prostrata (Lam.) Baillon (N. oleracea Lour.), from India, which is found in the tropical regions of North America, South America, and Asia. Loureiro was unaware that the plant had previously been described by Lamarck as a Mimosa (Encycl. 1: 10, 1783). Neptunia as delineated by Loureiro was distinguished primarily by the upper flowers of the heads containing antherbearing stamens, while those of the lower are neuter, having petaloid staminodes (Loureiro thought them petals). The genus was placed near Desmanlthus and Dichrostachys by some early taxonomists (De Candolle considered the latter genus and Neptunia no more than sections of Desmanthus), genera whose species often contain sterile filaments in the lowest flowers. Bentham (1842) noted the lack of constancy in this feature (e.g., Neptunia lutea has all its stamens anther-bearing) and placed Neptunia in his subtribe Adenantherae, which was distinguished from the subtribe Gymnantherae (containing Desmanthus and Dichrostachys) by having a small stipitate gland upon the anthers. Since then there has been no essential change in its generic status.