This "sensitive brier" is a procumbent ground-covering vine that occurs in southeastern states east of the Mississippi Rv. (K, W). It has often been treated as a variety of M. quadrivalvis L., along with several other taxa across North America. Typical quadrivalvis occurs in Tex. Typical microphylla is more closely related to M. nuttallii (DC. ex Britton & Rose) B.L. Turner, which is in central states largely west of the Mississippi (K). M. microphylla is at the edge of its range in se Ky. but locally frequent. It is largely restricted to rights-of-way on sandy uplands, and was probably more widespread before settlement in woodlands when burned and browsed along trails. It has a curious combination of high palatibility, before prickles develop, and sensitive folding leaflets. The sensisitivity of its leaflets, folding together when touched (seismonasty), is a trait that may have evolved several times within the genus. It is an expression of the more general ability of leaflets in Fabaceae, especially Mimosoideae, to move or fold in response to environmental cues (nyctinasty), often apparently in relation to threats of herbivory (Simon et al. 2011, Minorsky 2018). Crossing the Cumberland Plateau in 1867, John Muir (1916) noted: "...I found that Schrankia vines growing along foot-paths leading to a backwoods schoolhouse were much less sensitive than those in the adjacent unfrequented woods, having learned to pay but slight attention to the tingling strokes they get from teasing scholars."