| | 1. Spikelet ovoid; inflorescence open, branches spreading |
| |
| | 2. Palea tip jagged or widely V-notched; lemma widest at middle or below (sect. Hydropoa) |
| G. grandis |
| | 2' Palea tip narrowly notched; lemma widest above middle (sect. Striatae) |
| |
| | 3. Leaf blade 6–12 mm wide, thin; lower glume 0.8–1.2 mm |
| G. elata |
| | 3' Leaf blade 2–8 mm wide, firm; lower glume 0.4–0.8 mm |
| G. striata |
| | 1' Spikelet cylindric; inflorescence narrow, branches appressed (sect. Glyceria) |
| |
| | 4. Lemma glabrous between barely scabrous veins |
| G. borealis |
| | 4' Lemma minutely scabrous between distinctly scabrous veins |
| |
| | 5. Lemma tip generally rounded |
| G. leptostachya |
| | 5' Lemma tip jagged, longest between veins |
| G. occidentalis
|