1 Plant a shrub or tree (the culms perennial, woody, to 25 m tall), with complex branching systems from the upper nodes; leaves strongly dimorphic, those of the main culm sheathing, those of the branches or culm tips pseudopetiolate

1 Plant an herb (the culms annual, not truly woody, to 5 m tall), lacking complex branching systems from the upper nodes; leaves not dimorphic, none of them pseudopetiolate.

..2 Plant a robust grass, culms usually > 2 m tall and usually > 5 mm in diameter at the base

..2 Plant a small to medium grass, culms < 2 m tall and usually also < 5 mm in diameter at the base.

....3 Spikelets either modified into asexual, purplish bulblets, or partially or wholly concealed either by spines, hooks, and/or involucres, or partially or wholly concealed by being imbedded in a fleshy rachis or cob.

......4 Fertile spikelets either absent (spikelets modified into asexual, purplish bulblets) or variously spiny or bead like

......4 Fertile spikelets embedded in a fleshy rachis (resembling a rattail) or a cob

....3 Spikelets apparent, not covered, concealed, embedded, or modified by spines, hooks, or involucres.

........5 Spikelets 2-flowered, often dorsally compressed, falling entire at maturity (the abscission below the glumes), the upper floret usually bisexual, the lower one male or sterile.

..........6 Glumes often as long as or longer than the lemmas and concealing the florets; spikelets usually arranged in obvious pairs or triplets, with 1 spikelet sessile or shortly pedicellate and the other 1 (or 2) spikelets pedicellate (the pedicellate sometimes vestigial or absent)

..........6 Glumes (the lower or both) shorter than the lemmas (or the glumes absent); spikelets not organized in pairs or triplets

........5 Spikelets 1-, 2-, or many-flowered, usually terete or somewhat laterally compressed, either abscising at maturity above the glumes or if 2-flowered then both florets bisexual, or the upper sterile.

............ 7 Inflorescence of one or more spikes, the spikelets sessile (or very short-pedicelled) on the spike axis, 1-more per node, characteristically in 2-more ranks (these either on opposite sides of the axis or crowded on one side), the individual spikelets borne more-or-less touching one another.

............ ..8 Spikelets borne in a single terminal spike or raceme (an extension of the culm), usually 2-ranked on opposite sides of the axis

............ ..8 Spikelets borne on 1-many spikes (the spikes themselves arranged digitately, subdigitately, or racemosely on the culm) in 2 (or more) rows; spikelets often on one side of the spike axis

............ 7 Inflorescence paniculate, sometimes somewhat to very congested, but then not as above.

............ ....9 Spikelets with a single bisexual floret, and no staminate, sterile, or reduced florets present (occasional spikelets of Muhlenbergia can have 2-3 florets).

............ ......10 Glumes absent or reduced to tiny rudiments; palea 1-keeled; [of wetlands]

............ ......10 Glumes present; palea various; [habitats various].

............ ........11 Inflorescences dense and spikelike, symmetrical, cylindrical or ovoid, unbranched

............ ........11 Inflorescences loose and open, or if relatively dense, then with discernible branches, and thus lobed or asymmetrical.

............ ..........12 Lemmas awnless

............ ..........12 Lemmas awned

............ ....9 Spikelets with 2-many florets, including bisexual, staminate, reduced, or sterile flowers.

............ ............ 13 Glumes (one or both) nearly equaling or surpassing the most apical lemma of the spikelet, therefore partially or completely concealing the florets