1. Spikelet solitary on main stem (scape) (this is our only species with this characteristic)...F. schoenoides

1. Spikelets more than one per main stem (scape)...2

2. Saltwater species. Ligule absent. Achene 1.5-2 mm long ...F. castanea (Often placed incorrectly under F. spadicea according to FNA.) (Fimbristylis cymosa also may occur on seaside beaches or dunes. The latter is likewise eligulate and likewise has blunt scales, but the spikelets are 2-3 mm vs. 5-20 mm long, the achene is 1.5-2 mm vs. 1 mm long, and the inflorescence in F. castanea is usually compound vs. usually simple in F. cymosa.)

2. Freshwater species (F. caroliniana may be in brackish sites)...3

3. Styles 3-branched...F. autumnalis (Small grassy species, resembles Rhynchospora rariflora, but differs by having even-cymose branching and cylindric or lance-cylindric spikelets > 5 mm long vs. elliptic-ovate and < 5 mm long)

3. Style 2-branched...4

4. Ligule absent (see also F. castanea)...6

4. Ligule present...5

5. Blades 2-5 mm wide. Stem flattened and scabrous distally. Scales puberulent. Achene 1 mm long...F. caroliniana

5. Blades 2-3 mm wide. Stem somewhat flattened distally. Scales glabrous. Achene 1-1.2 mm long, ribbed...F. dichotoma

6. Spikelets > 5 mm long, with mucronate (with small tooth at the tip) scales...F. puberula

6. Spikelets < 5 mm long, with obtuse to notched scales (vs. mucronate in F. puberula and other freshwater species)...F. cymosa