Leaves with ligule membranous, ± ciliate, or a rim of hairs; blade rolled in bud, often with tubercle-based hairs.
Spikelets solitary or rarely in pairs, falling entire at maturity, usually dorsally compressed. Florets 2, the upper bisexual, the lower male or sterile. Lower glume often minute, 1–5-nerved or nerveless; upper rounded on the back, entire, 5–11-nerved. Lower lemma similar to the upper glume in texture and size, 5–9-nerved; upper lemma stiff or hardened, nerves usually not obvious, margins firm and inrolled, apex acute to obtuse, not mucronate. Paleas 2, the lower membranous or rarely absent, the upper similar to its lemma and tightly enclosed by it.
| | Key to the species | |
| 1 | Lower glume mostly 10–50% the length of the spikelet | 2 |
| Lower glume 50–90% the length of the spikelet (sometimes slightly less than half the spikelet length) | 14 |
| 2 | Lower floret almost always male (examine several spikelets) | 3 |
| Lower floret almost always sterile (stamens absent) (examine several spikelets)
Back to 1 | 7 |
| 3 | Fertile lemma smooth and shiny, occasionally faintly rugulose (with tiny wrinkles); panicle branches more or less whorled | 4 |
| Fertile lemma transversely rugulose (with a wrinkled appearance); lower panicle branches whorled
Back to 2 | Panicum maximum |
| 4 | Tufted, ascending annual with soft stems that can be compressed easily; spikelets acute to obtuse | Panicum schinzii |
| Perennials with firm stems; spikelets acute to acuminate
Back to 3 | 5 |
| 5 | Creeping plants with long rhizomes; tips of rhizomes and buds covered with sharp, hard scales; potential weed | Panicum repens |
| Tufted plants, rhizomes and stolons if present short; hard, sharp scales absent; pasture grasses or roadside weeds
Back to 4 | 6 |
| 6 | Spikelets ovate to lanceolate; fertile floret c. 2.3 mm long; plants robust, tufted, culms sometimes swollen at the base | Panicum antidotale |
| Spikelets elliptic; fertile floret 1.75–2.5 mm long; plants variable in habit often with short stolons and without a well-developed basal tuft of leaves
Back to 5 | Panicum coloratum |
| 7 | Low decumbent perennials 0.15–0.5 m high, stoloniferous or rooting at the lower nodes; inflorescences usually very narrow and less than 7 cm long, sometimes reduced to a primary axis with racemes, often only partly exserted from the leaves | 8 |
| Erect or ascending (occasionally trailing) tufted annuals or perennials with culms usually more than 0.2 m high; panicles spreading, branched and usually more than 7 cm long, more or less exserted from the leaves
Back to 2 | 10 |
| 8 | Semi-aquatic grass rooting freely at the nodes in mud around streams and swamps; spikelets 2.75–3.3 mm long, leaves with blade not constricted at the blade-sheath junction | Panicum obseptum |
| Grasses of rainforest floors and margins; spikelets 1.75–2.5 mm long; leaves with blade abruptly narrowed into the sheath at the base, almost subpetiolate; tubercle-based hairs often present on leaves
Back to 7 | 9 |
| 9 | Stems rather weak, 4- or 5- or more-noded; leaves with blade soft; panicle with few but spreading branches | Panicum pygmaeum |
| Stems more rigid, almost wiry, 7- or 8-noded; leaves with blade firm; panicle contracted
Back to 8 | Panicum lachnophyllum |
| 10 | Stout aquatic grass, stems often floating on water or erect; leaves with blade 8–20 mm wide; spikelets 3.5–4.5 mm long | Panicum paludosum |
| Tufted, non-aquatic grasses; leaves with blade to 10 mm wide
Back to 7 | 11 |
| 11 | Fertile floret only about half the length of the spikelet, the latter 3.5–4.5 mm long; fertile lemma 1.75–2 mm long; panicle lanceolate in outline, often nodding | Panicum buncei |
| Fertile floret no more than 1 mm shorter than the spikelet; panicle ovate or pyramidal in outline, usually erect
Back to 10 | 12 |
| 12 | Tufted perennial forming large, usually blue-green, tussocks 0.3–0.8 m or more high; internodes usually concealed by the leaf sheaths | Panicum decompositum |
| Usually more slender, tufted annuals, leaves yellow-green or green with a purple tinge; nodes usually visible
Back to 11 | 13 |
| 13 | Yellowish green, erect annual of inland floodplains; panicle branches spreading at maturity, main branches becoming flattened and broad towards their bases | Panicum laevinode |
| Often purple-tinged, decumbent, weedy annual; main branches of panicle slender and almost 3-angled at the base, primary branches spreading but secondary branches and spikelets remaining appressed to their axes
Back to 12 | Panicum gilvum |
| 14 | Lower floret almost always male | 15 |
| Lower floret almost always sterile (stamens absent)
Back to 1 | 16 |
| 15 | Spikelets obtuse; fertile lemma with faint transverse wrinkles; lowest internode of each stem thickened into a hard, corm-like base | Panicum bulbosum |
| Spikelets acute, fertile lemma smooth and shiny; base of plant sometimes thickened and nodular but corm-like structures absent
Back to 14 | Panicum antidotale |
| 16 | Spikelets 5–6.5 mm long | 17 |
| Spikelets less than 5 mm long
Back to 14 | 18 |
| 17 | Lower glumes 50% the length of the spikelet, acute; spikelets ovate-oblong to ovate to lanceolate, apiculate-acuminate | Panicum miliaceum |
| Lower glume at least 75% the length of the spikelet, long-acuminate; spikelets lanceolate and long acuminate
Back to 16 | Panicum queenslandicum |
| 18 | Lower glume obtuse to almost acute | Panicum subxerophilum |
| Lower glume acute to acuminate
Back to 16 | 19 |
| 19 | Lower glume at least 75% the length of the spikelets; spikelets 3–5(–7) mm long | Panicum queenslandicum |
| Lower glume 50% (or slightly less) the length of the spikelet
Back to 18 | 20 |
| 20 | Aquatic grass with stems floating in water or rooting at the nodes in mud; plants glabrous; grain purplish black | Panicum bisulcatum |
| Tufted, non-aquatic grasses, sometimes decumbent (but not rooting at the nodes); leaves usually with tubercle-based hairs; grains not black
Back to 19 | 21 |
| 21 | Inflorescence 4–20 cm long, a primary axis with racemes (rarely secondary branching); spikelets often gaping, pale to purple or blotched with purple, nodes usually glabrous | Panicum simile |
| Panicle with long spreading branches and secondary and higher order branching; colour contrast not obvious in spikelets; nodes usually hairy
Back to 20 | 22 |
| 22 | Leaves with blade 2–5 mm wide, flat or involute; palea of lower floret present; plants perennial | Panicum effusum |
| Leaves with blade 5–18 mm wide, flat; palea of lower floret often absent; plants annual
Back to 21 | Panicum capillare |
