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1 Spikelets with evident cross- venation throughout (cross veins not only confined to distal 1/2 of upper glumes or first lemmas); spikelets yellowish |
1 Spikelets with longitudinal veins only, the upper glumes without cross- venation or cross- venation only on distal 1/2 of upper glumes; spikelets green or greenish-purple. |
2 Spikelets 1.8-2.2 mm long; plants annual and forming sprawling mats |
2 Spikelets 2.4-6 mm long; plants annual or perennial, erect or decumbent and rooting at nodes but not typically mat-forming. |
3 Pedicels bearing 1-5 long, conspicuous hairs. |
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5 Plants cespitose perennials; culm internodes with papillose-based hairs; secondary inflorescence branches present; lower glumes with 1-3 rigid hairs |
5 Plants erect to decumbent annuals (often rooting at lower nodes); culm internodes glabrous or sparsely pubescent; secondary inflorescence branches rarely present; lower glumes lacking rigid hairs |
4 Spikelets paired (at least at mid-branch length). |
6 Spikelets 4.8-6 mm long |
6 Spikelets 2.5-4 mm long. |
7 Spikelets suffused with purple |
7 Spikelets primarily green. |
8 Panicle branches glabrous to pubescent, with or without some papillose-based hairs; spikelets 2.5-3.4 mm long; upper glumes without cross venation distally; culm nodes pubescent |
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3 Pedicels glabrous, scabrous or sometimes short- pilose, but not bearing long, conspicuous hairs. |
9 Margins of upper glumes and lower lemmas uniformly pilose- fringed |
9 Margins of upper glumes and lower lemmas glabrous or, if pilose, then the basal hairs shorter than the distal hairs (as in U. piligera). |
10 Spikelets 2.9-3.8 mm long. |
11 Spikelets paired, in 2-4 rows, the apices abruptly acuminate; glumes not spaced apart; leaf blades 7-20 mm wide |
11 Spikelets solitary, in 2 rows, the apices acute or rounded; glumes 0.3-0.5 mm apart; leaf blades 3-10 mm wide |
10 Spikelets 3.8-6 mm long. |
12 Upper half of second glume and first lemma with evident transverse veins connecting the longitudinal veins |
12 Upper half of second glume and first lemma without evident transverse veins. |
13 Spikelets glabrous, 4.5-6 mm long; panicles 6-25 cm long; sheaths with papillose-based hairs |
13 Spikelets usually pubescent, 3.8-4.9 mm long; panicles 3-12 cm long; sheaths lacking papillose-based hairs |