Desmodium glabellum is a species of flowering plant in the legume family Fabaceae. It is native to the eastern and central United States. It is commonly called Dillenius' tick-trefoil in honor of Johann Dillenius, a British botanist of German birth. It is also known as the tall tick-trefoil.
Desmodium glabellum is a herbaceous perennial plant. It grows to 5 feet tall with alternate palmately trifoliate leaves. Light pink to purplish flowers appear June through September. Seeds in sticky pods arranged in a row of 2-5 segments appear August–October. This species is very similar to Desmodium perplexum from which it was recently split.
Desmodium glabellum was first described as Hedysarum glabellum by the French botanist André Michaux in 1803. The type specimen was collected in a grassland in "Lower Carolina". Michaux described the stem of the species as nearly glabrous, hence the specific name glabellum and the corresponding common name smooth tick-trefoil (not to be confused with Desmodium laevigatum, which also goes by that common name). In 1825, the Swiss botanist Augustin de Candolle placed Hedysarum glabellum in genus Desmodium, and so Hedysarum glabellum is a basionym for Desmodium glabellum
The American physician, botanist, and politician William Darlington described Desmodium dillenii in 1837. Darlington's description was based upon an illustration of Hedysarum trifoliatum published by the German-born British botanist Johann Jacob Dillenius in 1732. Recognizing Dillenius' contribution, Darlington referred to Desmodium dillenii as Dillenius's Desmodium. In 1950, the American botanist Bernice Schubert rejected Desmodium dillenii as a nomen confusum (a term having no standing in the International Code of Nomenclature of 2018), which means "confusing name". In an attempt to resolve the confusion, Schubert split the taxon into two distinct taxa, a newly described Desmodium perplexum, and the previously described Desmodium glabellum. However, Schubert did not identify the plant in Dillenius' illustration. The matter remained unresolved until 2020 when the morphologies of the taxa in question were sufficiently clarified. Subsequently the plant in Dillenius' illustration was identified as Desmodium glabellum, and hence the name Desmodium dillenii is a synonym for Desmodium glabellum The common name Dillenius' tick-trefoil is often used to refer to Desmodium glabellum.
Desmodium glabellum is a member of the Desmodium paniculatum complex, a group of closely related taxa that also includes Desmodium paniculatum sensu stricto, Desmodium perplexum, Desmodium fernaldii, and the synonym Desmodium dillenii. Alternatively, some botanists lump these taxa into a single polymorphic species, Desmodium paniculatum sensu lato, in which case Desmodium glabellum becomes a synonym of Desmodium paniculatum.
Desmodium glabellum is native to the eastern and central United States. It grows in fields, woodland borders, and disturbed areas.