First glume present (vs. Axonopus), and often wrapped around. Fertile (upper) lemma rugose

1. Inflorescence branches whorled…U. maxima (upper lemma strongly rugose. Spikelet 2.7-3.6 mm. Lower glume 1/4-1/3 the spikelet length)

1. Inflorescence branches not whorled…2

2. Sheaths and leaf blades on both surfaces abundantly and conspicuously provided with erect, soft pilose hairs...U. texana

2. Sheaths and blades glabrous or pubescent, but not as described above...3

3. Spikelets paired…4

3. Spikelets solitary…6

4. Nodes pubescent, the leaf sheaths often pubescent with papilla-based hairs...5

4. Nodes glabrous...U. adspersa

5. Lower glume 1/5-1/3 the spikelet length, usually 1(3)-veined. Main inflorescence axes flat…U. mutica

5. Lower glume approx. 1/3 the spikelet length. Lower glume with 3 or more veins. Main inflorescence axes 3-angled...U. ramosa

6. Lower glumes scarcely separated. Lower glumes 5-7 veined and 1/3 the spikelet length. Spikelets 3.8-5 mm long…U. platyphylla

6. Lower glumes separated by a conspicious 0.3-0.5 internode. Lower glumes (7)9-11 veined...7

7. Spikelets 3.3-4 mm long. Lower glume 1/3-1/2 the spikelet length…U. subquadripara

7. Spikelets 4.5-6 mm long. Lower glume 1/3 the spikelet length…U. plantaginea