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1 Spikelet scales with mucros or cusps 0.7-2.5 mm long; achenes ellipsoid, 0.6-0.8 mm long, 0.3-0.5 mm thick, about 2× as long as thick; [historic waif]; [subgenus Micranthae]
1 Spikelet scales acute, obtuse, or with a mucro to 0.2 (-0.5) mm long; achenes obovoid and usually trigonous, 0.7-1.6 mm long, 0.4-1.1 mm thick, 1-1.5× as long as thick; [collectively widespread].
..2 Achenes with 5-8 longitudinal ridges, cross-linked by many, finer transverse ridges, making a fine reticulum (use at least 10× magnification); scales of the spikelet not gibbous, not clasping the achene when shed; scales reddish to black; [historic waif, but also sometimes cultivated); [subgenus Isolepis, section Isolepis]
..2 Achenes finely to coarsely papillate (use at least 10× magnification); scales of the spikelet either gibbous (boat-shaped) tending to clasp the shed achene, or only slightly curved, and not clasping the shed achene; scales greenish, straw-colored, or slightly orange; [collectively widespread]; [subgenus Isolepis, section Cernuae].
....3 Achenes with all or at least 2 sides convex; scales of the spikelet not gibbous (boat-shaped), and not retaining (by clasping) the shed achene