Beggar Lice, Beggar's Ticks, Panicled Tick Trefoil, Perplexed Tick Trefoil

From the Illinois Wildflower site:

"This Tick Trefoil species can produce large panicles of small flowers that are rather ...Read Moreshowy. It is one of the Desmodium spp. that blooms later in the year than many others. Unfortunately, it has been re-classified by taxonomists on several occasions, which may be the reason for the 'perplexum' in its scientific name. In some older sources of information, this plant is referred to as Desmodium dillenii and Desmodium glabellum. However, Desmodium glabellum is now considered a separate species with an appearance that is quite similar to Perplexing Tick Trefoil, while Desmodium dillenii is considered a defunct classification. Presumably, Desmodium perplexum and Desmodium glabellum can be distinguished as follows: 1) the former species has a faint reticulated network of veins on the lower surface of the leaflets, while the latter has a strong reticulated network of veins, and 2) the former species has hairs on the stems and leaves that are straight or somewhat curved, while the latter has hooked hairs. Other distinguishing features for Perplexing Tick Trefoil include inconspicuous stipules that are very narrow and deciduous (i.e., they wither away quickly), and petioles of the compound leaves that are at least ½" in length."