About Desmodium perplexum B.G.Schub.
Desmodium perplexum B.G.Schub. is a herbaceous perennial plant. It produces trifoliate leaves with petioles that are at least 10 mm (0.39 in) long. Its fruit is a legume known as a loment, which breaks apart into single-seeded segments covered in hooked hairs that stick to animal fur and human clothing. This species is morphologically very similar to Desmodium glabellum, and the two can only be told apart by a combination of fruiting and vegetative characteristics. Desmodium perplexum is native to eastern North America. In the United States, its recorded range stretches from southern Maine west to Iowa, south to eastern Texas, and east to Georgia. In Canada, members of the Desmodium paniculatum complex are known to occur in Ontario and Quebec, but Desmodium perplexum is treated as a synonym of Desmodium paniculatum in Canada, so the actual occurrence of this separate species there is unknown. Different sources disagree on the distribution of Desmodium perplexum across North America. This disagreement is likely caused by the absence of an identification key that can reliably distinguish between Desmodium perplexum and Desmodium glabellum. When researchers used a key published in 2020, they found that almost 60% of the herbarium specimens from Missouri had been incorrectly identified. After reclassifying these specimens, results showed Desmodium glabellum occurs across most of Missouri, while Desmodium perplexum is restricted to the Ozarks in the southeastern half of the state. The same 2020 key also supports the new claim that Desmodium glabellum is far more common than Desmodium perplexum in Pennsylvania, which contradicts earlier understandings of their distributions there.
