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Key to Fimbristylis

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1 Style branches 3; achene trigonous or terete; plant an annual.

2 Achene trigonous; spikelets linear-oblong to lanceolate, 3-7 mm long; ligule present, as a line of short, pale hairs  Fimbristylis autumnalis

2 Achene terete; spikelets subglobose to ovoid, 2-4 mm long; ligule absent  Fimbristylis littoralis

1 Style branches 2; achene lenticular or terete; plant an annual or perennial.

3 Plants diminutive annuals, the culms 1-6 (-30) cm tall; leaf blades < 1 mm wide.

4 Achene cylindrical, 2-4× as long as wide, curved like a tiny banana; inflorescence bracts 1-2 cm long  Fimbristylis perpusilla

4 Achene obovate, 1-1.5× as long as wide, not curved; inflorescence bracts 4-10 cm long.

5 Inflorescence diffuse, the spikelets stalked; base of style with recurved fimbriae  Fimbristylis squarrosa

5 Inflorescence compact, the spikelets sessile or subsessile, in a dense cluster; base of style smooth or papillate  Fimbristylis vahlii

3 Plants small to large annuals or perennials, the culms (6-) 15-150 cm tall; leaf blades > 1 mm wide.

6 Spikelets 2-3 mm long; inflorescence compact, complexly glomerate; achenes obovoid; [of peninsular FL and s. TX in our area]  Fimbristylis cymosa ssp. spathacea

6 Spikelets > 5 mm long; inflorescence at least partly diffuse, with spikelets stalked; achenes lenticular; [widespread in our area].

7 Plant a medium-sized to robust perennial, the culms generally 5-15 dm tall, either cespitose, with a hardened base, and deeply set in the substrate, or rhizomatous, the rhizomes either slender or thick

8 Plant cespitose, lacking rhizomes; bases of leaves hard, leathery, dark brown, deeply set in the substrate, the base of the plant generally 5-15 cm below the ground surface; achene (1.3-) 1.5-2 mm long  Fimbristylis castanea

8 Plant rhizomatous, the rhizomes either thick and knotty or slender and scaly (rarely with both); bases of leaves often somewhat thickened, hardened, and brownish, the base of the plant not especially deeply set; achene 0.8-1.2 (-1.3) mm long.

9 Plant a robust perennial to 15 (-20) dm tall, with elongate, slender, scaly, pale-to-reddish rhizomes (excavate carefully); leaves usually flat or keeled, 2-5 mm wide; stem usually flattened and scabrous-edged above; ligule present, a line of short, pale hairs  Fimbristylis caroliniana

9 Plant a medium-sized perennial to 10 dm tall, rhizomatous, the rhizomes either short, thick, and knotty or also with slender rhizomes); leaves usually involute, ca. 1 mm wide; stem usually terete or oval in cross-section, smooth; ligule either absent or present.

10 Ligule present; sheaths and fertile scales glabrous; culm bases swollen, knotty, closely joined, forming short thick, knotty rhizomes; leaves and sheaths mostly glabrous; ligule present, mostly complete; involucral sheaths and fertile scales usually smooth.  Fimbristylis interior

10 Ligule absent or poorly developed; sheaths and fertile scales puberulent; culm bases not swollen, producing several slender, scaly, orange rhizomes; leaves and sheaths totally pubescent or glabrous; backs of involucral sheaths and fertile scales puberulent at least distally.  Fimbristylis puberula

7 Plant a small to medium-sized annual or perennial, the culms to 8 dm tall, neither rhizomatous (except F. brevivaginata) nor with a hardened base deeply set in the substrate.

11 Spikelets pale, usually solitary (-3) on the scape (and thus appearing somewhat like an Eleocharis)  Fimbristylis schoenoides

11 Spikelets dark, usually in a complex inflorescence.

Show caption*© Dan Spaulding, some rights reserved (CC BY-NC), uploaded by Dan Spaulding                        12 Face (one side) of the achene with 15 or more longitudinal rows of rounded pits, the achene margin noticeably paler  Fimbristylis tomentosa

Show caption*© Jay Horn                        12 Face (one side) of the achene with 13 or fewer longitudinal rows of rectangular pits, the achene margin not noticeably paler.

13 Plant a perennial; leaves spreading, 2-5 mm wide; achenes lacking warts.

Show caption*© Gemma C. Milly                             14 Plant bulbous at base, and also with scale-covered short rhizomes; spikelet scales glabrous or puberulent; [plant a rare native of rock outcrops in GA and AL]  Fimbristylis brevivaginata

Show caption*© Jay Horn Show caption*© Jay Horn                             14 Plant neither bulbous nor rhizomatous; spikelet scales glabrous; [plant weedy, probably introduced in North America]  Fimbristylis dichotoma

13 Plant an annual; leaves spreading or ascending, 1-4 mm wide; achenes with or without warts.

Show caption*© Scott Ward, some rights reserved (CC BY), uploaded by Scott Ward                               15 Achenes lacking warts or with warts scattered over the entire surface; primary rays of umbel spreading or ascending, the inflorescence generally longer than broad; leaves relatively soft  Fimbristylis annua

15 Achenes with a few low warts on the edges; primary rays of umbel stiffly spreading (even deflexed), the inflorescence therefore often as broad as long or broader; leaves relatively hard, broad (averaging 2 mm wide), and spreading subdistichously  Fimbristylis decipiens