1a	Stigmas 3	2
1b	Stigmas 2	12
2a	Glumes distichous at least in the lower part of spikelet	3
2b	Glumes spirally arranged	5
3a	Inflorescence reduced to single spikelets; involucral bract glume-like	F. ovata
3b	Inflorescence with more than two spikelets; involucral bract setaceous or foliaceous	4
4a	Perennials; involucral bract foliaceous; inflorescence a compound anthela; glumes glabrous	F. fusca
4b	Annual; involucral bract setaceous; inflorescence a simple or sub-compound anthela; glumes apically sparsely ciliate	F. fimbristyloides
5a	Leaf-sheath ligulate, with a fringe of short hairs	6
5b	Leaf-sheath eligulate	7
6a	Stem strongly compressed; involucral bract exceeding inflorescence; achene smooth	F. complanata
6b	Stem not compressed; involucral bract shorter than inflorescence; achene verruculose	F. thomsonii
7a	Spikelets in clusters	F. falcata
7b	Spikelets solitary	8
8a	Culm 3-angled	9
8b	Culm 4 or 5-angled	10
9a	Plant stoloniferous; culm with all leaves with a blade	F. pierotii
9b	Plant not stoloniferous; culms with 1–3 leafless sheaths	F. umbellaris
10a	Culm 4-angled; leaf blade bilaterally flattened, ensiform; spikelet globose	F. littoralis
10b	Culm 5-angled; leaf blade (if present) dorsoventrally flattened, linear; spikelets elongated	11
11a	Leaves with a blade; achene distinctly verruculose with 4–7 rows of transversely oblong epidermal cells	F. quinquangularis
11b	Leaves reduced to bladeless sheath; achene sparsely verruculose with more than 9 rows of transversely linear-oblong epidermal cells	F. salbundia
12a	Spikelets 1 to 3	13
12b	Spikelets several to many (sometimes, one or two spikelets in F.ferruginea, but glume is always apically puberulous)	15
13a	Leaves with a blade; achene smooth, pitted with hexagonal cells	F. schoenoides
13b	Leaves reduced to a bladeless sheath; achene coarsely rugulose with transverse wavy reticulation	14
14a	Involucral bracts glume-like; spikelet nodding; achene margin verruculose	F. nutans
14b	Involucral bract absent; spikelet erect; achene margin not verruculose	F. acuminata
15a	Leaves eligulate	16
15b	Leaves ligulate	20
16a	Annual	17
16b	Perennial	18
17a	Style base fringed with a whorl of long pendent hairs covering the upper half of the nut	F. squarrosa
17b	Style minutely ciliate at the top	F. aestivalis
18a	Rhizome creeping; culm sparsely tufted; spikelets not angular	F. rigidula
18b	Rhizome not creeping; culm densely tufted; spikelets slightly angular by the keeled glumes	19
19a	Leaves flat or canaliculate, apex abruptly acuminate; glumes keel glabrous	F. cymosa var. spathacea
19b	Leaves flat, apex subobtuse; glumes keel puberulous	F. fuscinux
20a	Plant bearing stolons	F. stolonifera
20b	Plant tufted, lacking stolons	21
21a	Glumes puberulous, broadly ovoid, margin apically ciliate, apiculate; achene smooth, obscurely pitted with hexagonal cells	F. ferruginea
22b	Glumes glabrous, margin hyaline, 3-veined, acute to apiculate; achene reticulate with transversely oblong cells	22
22a	Spikelets 1–1.5 mm wide, angular by the keeled glume; glumes to 1.5 mm long	F. bisumbellata
22b	Spikelets 2–4 mm wide, terete; glumes not keeled, over 1.5 mm long	F. dichotoma