This widespread weedy eastern species is perennial or annual; 2n = 28. It has been confused with scabra in earlier literature; see HC, FNA 24, M and W for details. A. scabra Willd. is a close relative of hyemalis, with larger spikelets that are less clustered; it appears somewhat intermediate between hyemalis and perennans. A. scabra is widespread across cool temperate and boreal regions of North America, also in East Asia; 2n = 42. All reports from Ky., and probably many from across southeasatern states, appear to have been based on misidentifications of perennans; mapping of W and K (2020) is dubious. A. hyemalis differs from scabra and perennans as follows (F, FNA 24, W): leaves 1-2 mm wide (versus 1-6 mm); spikelets 1.2-2 mm long (versus 1.8-3.7 mm); anthers 0.2-0.6 mm long (versus 0.3-0.8 mm); lemma never awned (versus awned or awnless); pedicels 0.1-3.5 mm (versus 0.4-9.6 mm); plants flowering in Mar-Jul (versus Jun-Nov). The key in F has been misleading: the "copiously spinulose-scabrous" panicle branches of both scabra and hyemalis are usually distinct from the "slightly scabrous" or "scabridulous" (FNA 24) branches of perennans, but other diagnostic differences should be sought. A. scabra reportedly differs from perennans as follows (F, FNA 24, W): leaves, at least the basal, mostly involute, 1-3 mm wide (versus 2-6 mm); panicle branches mostly forking well beyond the middle, as in hyemalis (versus at or below middle).