This annual is a globally rare diploid (2n = 22) of midwestern regions and the southern Great Plains (K); it was recently discovered in Ohio (McKenzie et al. 2015). It is considered threatened,endangered or locally extinct in all states except Neb., where clustered in just eight counties (NS). In Ky. it is known from only two localities in ephemeral sinkhole ponds within or near cropped fields. The site discovered by E.W. Chester in CHRI (APSC) is reduced and threatend by development. The site recently discovered by B. Palmer-Ball in LOGA (APSC) is close to a more natural area, Mosely Pond (Chester & Palmer-Ball 2011). At both sites, another globally rare annual plant has also been found: Helanthium parvulum [= Echinodorus tenellus var. parvulus].