Plants annual or perennial; synoecious, monoecious, or dioecious; primarily herbaceous, habit varied. Culms annual, usually solid, sometimes somewhat woody, sometimes decumbent, often branched above the base. Leaves distichous; sheaths usually open; auricles usually absent; abaxial ligules usually absent, occasionally present as a line of hairs; adaxial ligules membranous, sometimes also ciliate, or of hairs, sometimes absent; bladessometimes pseudopetiolate; mesophyll radiate or non-radiate; adaxial palisade layer absent; fusoid cells usually absent; arm cells usually absent; kranz anatomy absent or present; midribsusually simple, rarely complex; adaxial bulliform cells present; stomata with triangular or dome-shaped subsidiary cells; bicellular microhairs usually present, with a long, narrow distal cell; papillae absent or present. Inflorescences ebracteate (Paniceae) or bracteate (most Andropogoneae) panicles, racemes, spikes, or complex arrangements of rames (in the Andropogoneae), usually bisexual, sometimes unisexual; disarticulation usually below the glumes, frequently in the secondary and higher order axes of the inflorescences. Spikelets bisexual or unisexual, frequently paired or in triplets, the members of each unit usually with pedicels of different lengths or 1 spikelet sessile. Glumes usually 2, equal or unequal, shorter or longer than the adjacent florets, sometimes exceeding the distal florets; florets 2, usually dorsally compressed, sometimes terete or laterally compressed; lower florets sterile or staminate, frequently reduced to a lemma; upper florets usually bisexual; lemmas hyaline to coriaceous, lacking uncinate hairs, often terminally awned; awns single; paleas of bisexual floretswell-developed, reduced, or absent; lodicules usually 2, sometimes absent, cuneate, free, fleshy, usually glabrous; anthers 1-3; ovaries usually glabrous; haustorial synergids absent; style branches2, free and close or fused at the base. Caryopses: hila usually punctate; endosperm hard, without lipid; starch grains simple; embryos large in relation to the caryopses, usually waisted; epiblasts usually absent; scutellar cleft present; mesocotyl internode elongated; embryonic leaf margins usually overlapping, rarely just meeting. x = 5, (7), 9, 10, (12), (14).

The subfamily Panicoideae is most abundant in tropical and subtropical regions, particularly mesic portions of such regions, but several species grow in temperate regions of the world. Within the Flora region, the Panicoideae are represented by 59 genera and 364 species. They are most abundant in the eastern United States (Barkworth and Capels 2000). Photosynthesis may be either C₃ or C₄. All three pathways are found in the subfamily, but the PCK and NAD-ME variants appear to have evolved only once, while the NADP-ME pathways seems to have evolved several different times (Giussani et al. 2001).

The Panicoideae were first recognized as a distinct unit by Brown (1814), earlier than any of the other subfamilial taxa of the Poaceae. Its early recognition is undoubtedly attributable to its distinctive spikelets. Recognition of the tribe Gynerieae is recent (Sánchez-Ken and Clark 2001) and its placement in the Panicoideae, rather than the Centothecoideae, should be regarded as tentative.

Spikelets with two florets are found in many other subfamilies, but rarely do they follow the pattern of the lower floret being sterile or staminate and the upper floret bisexual. Development of unisexual florets within the Panicoideae appears to be consistent across the subfamily (LeRoux and Kellogg 1999), but differs from that in the Ehrhartoideae (Zaitcheck et al. 2000).

The Paniceae and Andropogoneae have their conventional interpretation in this Flora, so far as the North American taxa are concerned. Molecular studies, however, while strongly supporting the monophyly of the Andropogoneae, show the Paniceae to be paraphyletic, with two distinct clades. In one of these clades, most taxa have a chromosome base number of x = 9, but some have x = 10, and the taxa are pan-tropical in origin. The taxa in the other clade, with one exception, have a chromosome base number of x = 10 and are American in origin. This latter clade is sister to the Andropogoneae, which also have a chromosome base number of x = 10 (Gómez-Martínez and Culham 2000; Giussanni et al. 2001; Barber et al. 2002).