Desmodium is a genus of plants in the legume family Fabaceae, sometimes called tick-trefoil, tick clover, hitch hikers or beggar lice. There are dozens of species and the delimitation of the genus has shifted much over time. Species are distributed widely – from Quebec to northern Argentina in the Americas, across northern and southern tropical Africa, in the southern Arabian Peninsula, in Myanmar and Thailand, New Guinea, and northern and eastern Australia.

These are mostly inconspicuous plants; few have bright or large flowers. Though some can become sizeable plants, most are herbs or small shrubs. Their fruit are loments, meaning each seed is dispersed individually enclosed in its segment. This makes them tenacious plants and some species are considered weeds in places.

Several Desmodium species release organic compounds, aerially and into the soil, which make them useful for agriculture: Allelopathic compounds are used there via push-pull technology. For this Desmodium heterocarpon (now Grona heterocarpos), Desmodium intortum, and Desmodium uncinatum are inter-cropped in maize and sorghum fields to suppress witchweeds, including Asiatic witchweed (Striga asiatica) and purple witchweed (S. hermonthica) and to repel Chilo partellus, a stem-boring grass moth. Insects (including pests) are likewise repelled by high amounts of antixenotic allomones produced by Desmodium.

A blue dye is obtained from Desmodium incanum.

Tick-trefoils in agriculture can also be used as living mulch and as green manure, as they improve soil fertility via nitrogen fixation.

Most also make good fodder for animals including bobwhite, turkey, grouse, deer, cattle and goats.

Wild-living, non-farmed deer appear to rely on Desmodium species in certain areas, particularly during the more stressful summer months.

The caterpillars of the lesser grass blue (Zizina otis) and the two-barred flasher (Astraptes fulgerator) feed on tick-trefoils.