This diminutive annual is widely distributed across most temperate regions of the globe. It probably originated in western North America, where the genus is most diverse, and may have spread west after settlement (W). However, C.W. Short made collections from CHRI in 1818 (PH) and elsewhere in 1837 (NCU); his first colls. became named M. shortii Raf. in 1819 (M; Short et al. 1833). In Ky. it generally occurs on bare damp ground in cropped fields, or similar places, and it is probably much overlooked.