Eastern Trailing Ticktrefoil

Perennial, Herbs, Stems woody below, or from woody crown or caudex, Taproot present, Nodules present, Stems prostrate, trailing, or mat forming, Stems less than 1 m tall, Stems 1-2 m tall, Stems solid, Stems or young twigs glabrous or sparsely glabrate, Stems or young twigs sparsely to densely hairy, Leaves alternate, Leaves petiolate, Stipules conspicuous, Stipules green, triangulate to lanceolate or foliaceous, Stipules setiform, subulate or acicular, Stipules persistent, Stipules deciduous, Stipules free, Leaves compound, Leaves pinnately 3-foliolate, Leaves odd pinnate, Leaf or leaflet margins entire, Leaflets opposite, Stipels present at base of leaflets, Leaflets 3, Leaves hairy on one or both surfaces, Inflorescences racemes, Inflorescence panicles, Inflorescence terminal, Bracts very small, absent or caducous, Bracteoles present, Flowers zygomorphic, Calyx 2-lipped or 2-lo bed, Calyx hairy, Petals separate, Corolla papilionaceous, Petals clawed, Petals blue, lavander to purple, or violet, Banner petal ovoid or obovate, Wing petals narrow, oblanceolate to oblong, Wing tips obtuse or rounded, Keel tips obtuse or rounded, not beaked, Stamens 9-10, Stamens diadelphous, 9 united, 1 free, Filaments glabrous, Style terete, Fruit a loment, jointed, separating into articles, Fruit unilocular, Fruit indehiscent, Fruit elongate, straight, Fruit exserted from calyx, Fruit compressed between seeds, Fruit hairy, Fruit 3-10 seeded, Seeds ovoid to rounded in outline, Seeds reniform, Seed surface smooth, Seeds olive, brown, or black.

Desmodium × humifusum is a species of flowering plant in the legume family known by the common names trailing tick-trefoil, eastern trailing tick-trefoil, and spreading tick-trefoil. It is native to the eastern United States, where it has been reduced to scattered populations in the states of Massachusetts, Connecticut, and Indiana. It once had a wider distribution but it has likely been extirpated from Delaware, Maryland, New Jersey, New York, Rhode Island, Virginia, West Virginia, and Missouri.

This plant is prostrate, its hairy stems trailing up to 2 metres (7 ft) long. One plant may have a large number of stems. The alternately arranged leaves are each divided into 3 leaflets up to 7 centimetres (3 in) long by 5 centimetres (2 in) wide. The leaves have persistent stipules which may aid in identification. The inflorescence is a raceme of purple flowers nearly one centimeter long. Blooming occurs in July and August. The fruit is a legume pod jointed into three or four segments, with each segment up to 8 millimetres (1⁄3 in) long. The segments are dispersed on animal fur. This species is probably a hybrid of Desmodium paniculatum and D. rotundifolium.

This plant grows on sandy soils that originated from sandstone and chert. The habitat is often dominated by oaks, and it may be a type of dry forest.