Its fruit is a type of legume called a loment that separates into single-seeded segments with hooked hairs that stick to fur and clothing.

The two species may be distinguished by a combination of fruiting and vegetative characters:[4][5] Desmodium perplexum was first described by the American botanist Bernice Schubert in 1950.

[6] The type specimen was collected by Fernald and Long in Sussex County, Virginia in September 1945.

[7] The specific name perplexum refers to the "perplexity of botanists" concerned with the taxon known as Desmodium dillenii Darl.

[14] In the United States, its range extends from southern Maine, west to Iowa, south to eastern Texas, and eastward into Georgia.