This annual occurs mostly in the central and lower Mississippi Valley, plus the adjacent Gulf Coastal Plain (FNA 24). It may be generally associated with relatively base-rich clayey soils that have a xerohydric tendency, as in the "clay barrens" among post-oak flatwoods in s. Ind. (Homoya 1994). A. ramosissima can appear similar to longespica (or geniculata), but it differs as folllows (FNA 25, W): emmas 8-22 mm long (versus 2.5-10 mm); central awn curved about 180 degrees at the base and recurved into a semicircular bend (versus about 90 degrees in a simple bend). A. ramosissima can also appear similar to oligantha, since it sometimes has lower glumes with 3-7 veins (versus 1-2 in most species of the genus); but oligantha is distinct in its relatively equal awns.