1) Inflorescence an open panicle
Amphicarpum - White line around the leaf edge. Underground and above-ground flowers.
Dichanthelium - basal rosette (only forms in N. Florida in some spp.), C3, looks like small Panicum with wide leaves and ball shaped panicle, never has hard leaves, always blunt spikelets .
Lasiacus - Bamboo like vegetatively.
Leptoloma - Very open panicle with long pointed spikelets at tips of branches - sandhill (rare).
Oplismenus - ovate wavy leaves. (1 sp.)
Panicum - If it isn't the others it must be Panicum.
Rhynchelytrum/Melinis - 2nd glume and sterile lemma awned from a notched tip. (v. hairy) M. repens.
Sacciolepis - Spikelets hard at tip with a swelling at base. S. indica fls are < 3mm long & S. striata fls. are > 3mm long.
Urochloa/Brachiaria - some say this is one genus, can have either a panicle of spikes or an open panicle, 1st glume faces rachis alot of time. Difficult group.
2) Inflorescence somewhat spikelike
Cenchrus - spike - flowers in a spiny burr
Pennisetum - single spike or compressed panicle - bristles - pointed spikelets.
Setaria - single spike or compressed panicle - bristles - rounded spikelets.
Stenotaphrum - Single fleshy spike (St. Augustine Grass)
3) One sided spikes/racemes - either paired or alternate.
Axonopus - 1st glume absent - fertile lemma backing against the rachis. The 2 racemes of an entire population appear to be at the same angle.
Digitaria - Spikelets pointed, lemma loose, thin - not clasping the palea. Digitate.
Echinochloa - Often with various size awns and spikelets erect from the axis.
Eriochloa - first glume tiny - modified into a tiny cup.
Paspalidium - floating aquatic Paspalum (paried racemes).
Paspalum - Spikelets a half-sphere, flat on one side.
Reimarochloa - no glumes.