Flora of the Southeastern United States
2022 Edition

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Key to Rhynchospora

1 Tubercles 3-23 mm long; style simple or bifid only at the tip; [subgenus Haplostylae]
1 Tubercles < 3 mm long; style divided into 2 slender stigmatic branches; [subgenus Diplostylae].
..2 Inflorescence bracts several, foliaceous, basally bright white, reflexed to horizontally spreading; [subgenus Diplostylae; section Dichromena]
..2 Inflorescence bracts 0-several, capillary to foliaceous, green throughout (stramineous in age), variously oriented.
....3 Bristles present, plumose (at least towards their bases); [subgenus Diplostylae; section Plumosae]
....3 Bristles absent, or present and smooth or minutely barbed.
......4 Bristles present, retrorsely barbed (at least towards their tips), or antrorsely barbed and straplike (flattened); [subgenus Diplostylae; section Albae]
......4 Bristles absent, or present and smooth, or antrorsely barbed and filiform.
........5 Achene surface smooth, minutely pitted, or finely striate (not ridged, rugose, or reticulate); [subgenus Diplostylae; sections Chapmaniae, Fasciculares, and Fuscae]
........5 Achene surface transversely ridged, rugose, or honeycombed-reticulate (sometimes faintly so); [subgenus Diplostylae; sections Globulares, Harveyae, Mixtae, Psilocarya, Pusillae, and Rariflorae]

Key to Rhynchospora, Key A: beaksedges with tubercles 3-23 mm long
[subgenus Haplostylae; sections Longirostres and Polycephalae]

1 Spikelets arranged in globose or subglobose clusters; tubercle 3-5 mm; leaf blades 2-8 mm wide.
..2 Spikelets arranged in subglobose, umbel-like clusters; achene margins crimped; plants not rhizomatous; [section Longirostres]
..2 Spikelets arranged in tightly globose clusters; achene margins not crimped; plants rhizomatous; [section Polycephalae]
1 Spikelets in > 4 paniculate or corymbose clusters; tubercle 10-23 mm long; leaf blades 6-20 mm wide; [section Longirostres].
....3 Longest bristles shorter than the achene
....3 Longest bristles longer than or equaling the achene.
......4 Plants cespitose; primary clusters with 10-50 (rarely 7 or fewer) densely clustered spikelets; achene (4.5-) 5-6 mm long
......4 Plants rhizomatous; primary clusters with 1-6 loosely clustered spikelets; achene (3.5-) 4.0-4.8 mm long.
........5 Bristles 2-8 mm long, the central bristle longest on one face, shortest or absent on the other
........5 Bristles 7-12 mm long, essentially of equal length

Key to Rhynchospora, Key B: beaksedges with basally-white bracts (White-bracted Sedges) [subgenus Diplostylae; section Dichromena]

1 Plant cespitose; achene+tubercle 0.8-1.2 mm long.
..2 keel of lower spikelet scales ciliolate; achene tubercle blunt or apiculate; [s. peninsular FL]
..2 keel of lower spikelet scales not ciliolate; achene tubercle with a short (0.2-0.3 mm long) beak; [OK and TX]
1 Plant rhizomatous; achene+tubercle 1.5-2.0 mm long.
....3 Inflorescence bracts 3-6 (-7); basal bract (1.4-) 2-5 mm wide, the white portion (2.5-) 9-25 mm long, tapering gradually into the green portion; rhizomes slender, straight, (0.6-) 0.7-1.7 (-2.1) mm in diameter; achene 1.0-1.2 mm wide; tubercle broadly truncate on achene
....3 Inflorescence bracts (5-) 6-10; basal bract 5-12 mm wide, the white portion 22-55 mm long, tapering abruptly into the green portion; rhizomes often bent and swollen at the nodes, 1.4-3.8 mm in diameter; achene 1.2-1.5 mm wide; tubercle decurrent on achene

Key to Rhynchospora, Key C: beaksedges with plumose bristles [subgenus Diplostylae; section Plumosae]

1 Spikelets borne singly or a few together in loose clusters, some or all spikelets on slender stalks; achene 1.7-2.6 mm long, 1.2-2.0 mm wide.
..2 Achene obovoid, 1.7-2.0 mm long, 1.2-1.5 mm wide, the tubercle seated on its summit without a constriction or basal flange; longer bristles < ½ as long as the achene
..2 Achene broadly elliptic, 1.9-2.6 mm long, 1.5-2.0 mm wide, its summit constricted below a collar-like flange at the base of the tubercle; longer bristles three-fourths to exceeding the length of the achene
1 Spikelets borne several to many in clusters, none of the spikelets on slender stalks; achene 1.3-2.2 mm long, 0.9-1.7 mm wide
....3 Leaves (1-) 2-4 mm wide, slightly involute (V-shaped in ×-section) near the base; achene 1.8-2.2 mm long; [FL only].
......4 Spikelets 8-10 mm long; fertile scales 5-8 mm long; perianth bristles 5-8 mm long
......4 Spikelets 3.5-6 mm long; fertile scales 3-3.5 (-4) mm long; perianth bristles extending to about the tubercle apex
....3 Leaves 0.3-1.5 mm wide, strongly involute (and often appearing superficially terete) throughout their length; achene 1.3-2.1 mm long; [collectively more widespread].
........5 Basal sheaths shiny, dark brown; bristles longer than the tubercle; bristles plumose in a basal zone that extends 4-20% of the length of the bristle, then with a smooth zone, the terminal zone minutely denticulate; [Gulf Coastal Plain of FL, AL, and MS]
........5 Basal sheaths dull, light to medium brown; bristles shorter than the tubercle; bristles plumose in a basal zone that extends 40-90% of the length of the bristle, the terminal zone minutely denticulate (lacking a smooth middle zone); [widespread in the Atlantic and Gulf Coastal Plain from NC south to FL, west to TX]

Key to Rhynchospora, Key D: beaksedges with bristles retrorsely barbed (at least distally)
or antrorsely barbed and straplike (flattened) [subgenus Diplostylae; section Albae]

1 Bristles 8-25, retrorsely barbed distally, antrorsely barbed proximally; spikelets white, turning tan with age.
..2 Spikelets with 2-3 florets; bristles 8-12; achene 1.6-2.1 mm long, 0.9-1.3 mm wide
..2 Spikelets with 1 floret; bristles 16-25; achene 2.0-2.4 mm long, 1.3-1.5 mm wide
1 Bristles 6 or fewer, either retrorsely or (rarely) antrorsely barbed their entire length; spikelets variously brown, rufous, or tan (or very rarely white).
....3 Spikelets 1-fruited, the solitary achene terminating the axis; clusters 1-7, globose to turbinate.
......4 Clusters globose to turbinate; achene (measured from base of bristles) 1.3-1.8 mm long, 0.65-0.95 mm wide; tubercle 0.7-1.6 mm long.
........5 Clusters turbinate to hemispheric (rarely subglobose), the lowest spikelets usually spreading-ascending to spreading; larger leaves < 2 mm wide; achene 1.6-1.8 mm long; tubercle 1.0-1.6 mm long
........5 Clusters globose to subhemispheric, the lowest spikelets usually reflexed; larger leaves > 2 mm wide; achene 1.3-1.6 mm long; tubercle 0.7-1.2 mm long
......4 Clusters globose to hemispherical; achene (measured from base of bristles) 1.8-2.6 mm long, 1.1-1.8 mm wide; tubercle 1.4-2.4 mm long.
..........6 Achene 1.1-1.2 mm wide, 1.8 mm long
..........6 Achene 1.2-1.8 mm wide, 2.1-2.6 mm long
....3 Spikelets 1-5 fruited (if 1-fruited, then the axis terminated by a sterile floret); clusters 2-many, ovoid to turbinate (rarely globose).
............ 7 Clusters numerous, usually 20 or more; tubercle 1.3-1.8 mm long; achene 0.9-1.5 mm wide, 1.5-2.0 mm long, the summit narrowly truncate, the faces umbonate, the margin thickened and wire-like; leaves 2.5-7 mm wide
............ ..8 Achene face medium brown, body 0.9-1.1 mm wide, the expanded portion above the gynophore 1.0-1.1 mm long, the gynophore slender and long
............ ..8 Achene face dark brown, body 1.2-1.5 mm wide, the expanded portion above the gynophore 1.3-1.4 mm long, the gynophore thick and short
............ 7 Clusters 2-8; tubercle 0.4-1.2 mm long; achene 0.6-1.2 mm wide, 1.1-2.0 mm long, the summit more rounded than truncate, the faces lenticular, a wire-like margin narrow or not evident; leaves 0.2-3.5 mm wide.
............ ....9 Achene 0.6-0.8 mm wide, 1.1-1.3 mm long; tubercle 0.4-0.6 mm long; bristles more-or-less equaling the achene
............ ....9 Achene 0.8-1.2 mm wide, 1.3-2.0 mm long; tubercle 0.8-1.6 mm long; bristles more-or-less equaling the tubercle.
............ ......10 Inflorescence typically with 1 terminal and 1 lateral cluster, the clusters ovoid, with 1-10 spikelets each; achene 1.8-2.0 mm long, 0.8-1.0 mm wide, 2-3 × as long as wide; leaves 0.2-0.4 mm wide
............ ......10 Inflorescence with 1-6 lateral clusters, the clusters turbinate with usually > 10 spikelets; achene 1.3-1.8 mm long, 0.9-1.2 mm wide, 1.5-2 × as long as wide; leaves 1.5-3.5 mm wide.
............ ........11 Longer bristles 0.4 mm shorter than to 0.3 mm longer than the tubercle; tubercle 0.9-1.4 (-1.6) mm long, on average 0.69× as long as achene body; glomerules 3-5 (-6), 6-13 mm wide; [widespread in our area]
............ ........11 Longer bristles 0.3-1.0 mm longer than the tubercle; tubercle 0.8-1.1 mm long, on average 0.57× as long as achene body; glomerules 4-8, 4-8 mm wide; [of the Coastal Plain]

Key to Rhynchospora, Key E: beaksedges with bristles smooth, or antrorsely barbed and filiform,
or absent, the achene surface smooth, minutely pitted, or finely striate
[subgenus Diplostylae; sections Chapmaniae, Fasciculares, and Fuscae]

1 Bristles 12; [section Fasciculares]
1 Bristles 6 or fewer.
..2 Leaves with a short taper at the tip, blunt to acute, but not long-acuminate; achene surface minutely pitted near the margin; [section Chapmaniae].
....3 Basal leaves 4-6 mm wide, ciliate, rosulate; scales acuminate, the midrib ciliate; bristles 6, < ½ the length of the achene
....3 Largest basal leaves 2.5-3 mm wide, eciliate, not rosulate; scales aristate, the midrib eciliate; bristles 3-4, 1 or more equaling or exceeding the tubercle
..2 Leaves long-acuminate at the tip; achene surface smooth or finely striate.
......4 Bristles absent or 1-3 rudimentary; scales white to pale tan (or pale reddish-brown in R. brachychaeta); [section Chapmaniae].
........5 Inflorescence composed of (1-) 2-3 turbinate to ellipsoid clusters; spikelets pale reddish-brown, (2.7-) 3-3.5 mm long; achenes usually 2 per spikelet
........5 Inflorescence composed of 1 (-2) hemispheric to broadly turbinate cluster(s); spikelets white to pale brown, either 2-2.5 (-3) mm or (3.5-) 4-5.5 mm long; achenes 1 per spikelet.
..........6 Base of plant not bulb-like, not enclosed in bladeless sheaths; spikelets 2-2.5 (-3) mm long; achene 1.0-1.2 mm long, 0.8-1.0 mm wide
..........6 Base of plant bulb-like, enclosed in bladeless sheaths; spikelets (3.5-) 4-5.5 mm long; achene 1.4-1.8 mm long, 1.2-1.5 mm wide
......4 Bristles present (if rudimentary, then 4-6); scales tan, rufous, or brown.
............ 7 Achene 0.6-1.1 mm wide, pyriform, obovoid, or narrowly elliptic, pale to dark brown but not blackish; tubercle margin setose.
............ ..8 Inflorescence of 1 cluster; tubercle 0.3-0.4 mm long, the margin smooth
............ ..8 Inflorescence of (1-) 2-4 (-10) clusters; tubercle 0.4-1.4 mm long, the margin setose; [section Fuscae].
............ ....9 Achene narrowly elliptic or narrowly obovoid, 1.2-1.5 mm long by 0.6-0.7 mm wide, twice as long as wide; tubercle 0.8-1.2 mm long
............ ....9 Achene broadly elliptic to obovoid or pyriform, < 2× as long as wide; tubercle 0.4-1.5 mm long.
............ ......10 Leaves 2-4 (-5) mm wide; stipe subtending achene 0.5-1.0 mm long
............ ......10 Leaves 0.2-1.5 (-2) mm wide; stipe subtending achene < 0.4 mm long.
............ ........11 Leaves to 1.5 (-2) mm wide; achene 1.0-1.7 mm long, 0.9-1.1 mm wide; tubercle 0.5-1.5 mm long.
............ ..........12 Culms solitary to loosely cespitose by slender rhizomes; terminal internode straight; clusters turbinate to ovoid; achene 1.0-1.3 mm long, uniformly medium to dark brown; tubercle 0.7-1.5 mm long; bristles usually of two lengths, some equaling the tubercle, and some equaling or shorter than the achene
............ ..........12 Culms solitary to cespitose, without slender rhizomes; terminal internode often arched; clusters corymbose to hemispheric; achene 1.3-1.7 mm long, pale to reddish-brown, often translucent centrally, with a distinctly thickened wire-like margin; tubercle 0.5-1.0 mm long; all bristles more-or-less equaling the tubercle
............ ........11 Leaves filiform, < 1 mm wide; achene 0.8-1.3 mm long, 0.6-0.9 mm wide; tubercle 0.4-0.8 mm long.
............ ............ 13 Culms without rhizomes; spikelets 2.5-5 mm long; achene translucent centrally; tubercle 0.4-0.7 mm long.
............ ............ ..14 Achene 0.5-0.8 mm wide; tubercle 0.4-0.6 mm long
............ ............ ..14 Achene 0.8-0.9 mm long; tubercle 0.6-0.7 mm long
............ ............ 13 Culms with delicate rhizomes; spikelets 5-7 mm long; achene uniformly opaque; tubercle 0.6-0.8 mm long
............ 7 Achene > 1 mm wide (except 0.8 mm wide in R. fernaldii with a blackish surface), suborbicular or broadly ellipsoid; tubercle margin smooth or roughened but not setose; [section Fasciculares].
............ ............ ....15 Achene 0.9-1.0 mm long, 0.8 mm wide, blackish
............ ............ ....15 Achene 1.3-4.2 mm long, 1.1-3.6 mm wide, brown to dark brown.
............ ............ ......16 Achene 2.0-4.2 mm long, 2.0-3.6 mm wide.
............ ............ ........17 Leaves 2-4 mm wide; achene 2.0-2.7 mm long, 2.0-2.5 mm wide
............ ............ ........17 Leaves 4-8 mm wide; achene 3.0-4.2 mm long, 3.0-3.6 mm wide
............ ............ ......16 Achene 1.3-2.0 mm long, 1.1-1.7 mm wide.
............ ............ ..........18 Tubercle 1.0-2.6 mm long, long-attenuate to subulate
............ ............ ..........18 Tubercle 0.2-0.8 mm long, triangular to triangular-attenuate or with a strap-like beak.
............ ............ ............ 19 Bristles rudimentary to ½ as long as the achene body.
............ ............ ............ ..20 Larger leaves to 1 mm wide; mature culms to 4.5 dm long; floral fascicles 1 (-2); tubercle 0.2-0.5 mm long
............ ............ ............ ..20 Larger leaves 2-4 mm wide; mature culms to 13 dm long; floral fascicles (1-) 2-4; tubercle 0.4-0.7 mm long
............ ............ ............ 19 Bristles > ½ as long to exceeding the achene body.
............ ............ ............ ....21 Basal leaves filiform to (rarely)1.3 mm wide, the longer approaching length of culm; tubercle narrowed above the base into a strap-like beak
............ ............ ............ ....21 Basal leaves 1.3-4 mm wide, all much shorter than the culm; tubercle triangular to triangular-attenuate.
............ ............ ............ ......22 Longer bristles equaling to exceeding the achene body; achene body elliptic, 1.1-1.3 mm wide; tubercle triangular-attenuate; larger basal leaves 1.3-2.5 mm wide
............ ............ ............ ......22 Longer bristles < ½ as long to exceeding achene body; achene suborbicular, 1.2-1.5 mm wide; tubercle triangular; larger basal leaves 2-4 mm wide

Key to Rhynchospora, Key F: beaksedges with bristles smooth, or antrorsely barbed and filiform, or absent,
the achene surface transversely ridged, rugose, or honeycombed-reticulate
[subgenus Diplostylae; sections Globulares, Harveyae, Mixtae, Psilocarya, Pusillae, Rariflorae]

1 Bristles absent (or apparently so at 10×); achene 0.5-0.7 mm wide; tubercle 0.1-0.2 mm long, skull-cap like; [section Pusillae].
..2 Achene including tubercle 1.0-1.2 mm long, the achene surface evidently reticulate and obscurely transversely ridged, the body ellipsoid; bristles present, white, barely visible at 20×, the longest shorter than the achene body
..2 Achene including tubercle 0.6-0.9 mm long, the body obovoid; bristles absent.
....3 Achene surface smooth, faintly reticulate, not transversely ridged
....3 Achene surface rough, distinctly transversely ridge
1 Bristles present or absent; if absent, then the achene > 1 mm long or > 0.7 mm wide, and tubercle triangular to subulate.
......4 Culms and leaves filiform.
........5 Achene including tubercle 1.0-1.2 mm long; tubercle minute, skullcap-like; [section Pusillae]
........5 Achene including tubercle 1.5-2.9 mm long; tubercle triangular to triangular-acuminate; [section Rariflorae].
..........6 Bristles subequaling to exceeding the tubercle; tubercle 0.75-1.4 mm long
..........6 Bristles shorter than the achene body; tubercle 0.3-1.0 mm long.
............ 7 Achene 1.3-1.6 mm long, 0.9-1.4 mm wide; tubercle 0.3-0.6 (-0.75) mm long; bristles 1/3-1/2(-4/5) as long as achene body
............ 7 Achene 1.6-1.8 mm long, 1.35-1.5 mm wide; tubercle 0.6-1.0 mm long; bristles 2/3 to nearly as long as achene body
......4 Culms stouter; leaves wider, not filiform.
............ ..8 Achene faces flat or concave; when one face is concave, the opposite face is sometimes slightly convex (slightly biconvex R. decurrens and R. microcarpa are keyed here for convenience).
............ ....9 Achene at least twice as long as wide, elliptic-oblong; tubercle subulate, 0.8-1.2 mm long; [section Mixtae]
............ ....9 Achene < twice as long as wide, obovate; tubercle triangular, 0.2-0.9 mm long.
............ ......10 Longer bristles exceeding the achene body.
............ ........11 Achene ±2.2 mm long, ±1.8 mm wide; tubercle ±0.9 mm long; [section Globulares]
............ ........11 Achene 0.8-1.2 mm long, 0.7-1.2 mm wide; tubercle 0.2-0.5 mm long; [section Mixtae].
............ ..........12 Larger leaves (3-) 4-6 mm wide; bristles exceeding tubercle; achene faces flattened
............ ..........12 Larger leaves 1-3 (-4) mm wide, bristles half as long as achene to equaling tubercle; achene faces slightly convex
............ ......10 Longer bristles shorter than to equaling achene body, or absent.
............ ............ 13 Larger leaves 3-5 mm wide; achene 1.4-1.6 mm wide; tubercle 0.6-0.8 mm long, abruptly rising from a flaring basal collar; [section Globulares]
............ ............ 13 Larger leaves 1-3 (-4) mm wide; achene 0.7-1.3 mm wide; tubercle 0.15-0.5 mm long, without a flaring basal collar; [section Mixtae].
............ ............ ..14 Bristles rudimentary or absent
............ ............ ..14 Bristles one-half as long to equaling achene.
............ ............ ....15 Achene 1.3-1.8 mm long, 0.9-1.2 mm wide, the faces flat with 10-12 transverse ridges
............ ............ ....15 Achene 0.8-1.4 mm long, 0.7-1.2 mm wide, the faces slightly biconvex with 6-12 transverse ridges.
............ ............ ......16 Clusters elongate; achene 1.0-1.4 mm long, 0.8-1.0 mm wide, narrowly obovate to elliptic, averaging 8-12 transverse ridges; most tubercle bases convexly seated on the achene summit and somewhat decurrent along the achene margins, the tubercle surface often whitish-waxy
............ ............ ......16 Clusters usually compact; achene 0.8-1.2 mm long, 0.7-1.2 mm wide, suborbicular to elliptic, averaging 6-7 transverse ridges; most tubercle bases flat across the achene summit, not decurrent, the tubercle surface usually dark, not waxy
............ ..8 Achenes biconvex or tumid.
............ ............ ........17 Achene 1.4-4.2 mm long, 1.2-3.6 mm wide, the summit with a thickened bony to crustaceous rim surrounding the base of the tubercle; [section Harveyae].
............ ............ ..........18 Achene lenticular and transversely ridge, ±1.4 mm long, ±1.2 mm wide
............ ............ ..........18 Achene tumid, lightly pitted or cancellate in a honeycomb pattern, 1.5-4.2 mm long, 1.4-3.6 mm wide.
............ ............ ............ 19 Leaves 4-8 mm wide; achene 3.0-4.2 mm long, 3.0-3.6 mm wide
............ ............ ............ 19 Leaves 2-4 mm wide; achene < 2.7 mm long and < 2.5 mm wide.
............ ............ ............ ..20 Achene 2.0-2.7 mm long, 2.0-2.5 mm wide
............ ............ ............ ..20 Achene 1.5-1.9 mm long, 1.4-1.7 mm wide
............ ............ ........17 Achene 0.7-1.8 mm long, 0.7-1.5 mm wide, the summit without a textured rim surrounding the base of the tubercle (if the base of the tubercle is rim-like, then it is distinguished from the summit of the achene by a constriction or articulation).
............ ............ ............ ....21 Bristles absent; achene 0.7-1.0 mm long; [section Psilocarya].
............ ............ ............ ......22 Tubercle triangular-lanceolate, as long as broad or longer; achene weakly transversely ridged
............ ............ ............ ......22 Tubercle depressed, broader than long; style not persistent; achene strongly transversely ridged
............ ............ ............ ........23 Spikelets (5-) 6-10 mm long, tan or brown, with an acuminate tip; tubercle ends upturned away from the achene
............ ............ ............ ........23 Spikelets 4-6 (-8) mm long, dark brown to black, with an acute tip; tubercle ends accrescent to the achene
............ ............ ............ ....21 Bristles present (occasionally detached in R. decurrens and R. miliacea with achenes 1.0-1.4 mm long); achene 0.8-1.9 mm long.
............ ............ ............ ..........24 Bristles not exceeding the achene body.
............ ............ ............ ............ 25 Cluster branches flexuous; bristles one-half as long to equaling the achene (or longer in R. microcarpa); achene slightly biconvex, 0.8-1.4 mm long, 0.7-1.0 (-1.2) mm wide; [section Mixtae].
............ ............ ............ ............ ..26 Clusters elongate; achene narrowly obovate to elliptic, averaging 8-12 transverse ridges; most tubercle bases convexly seated on the achene summit and somewhat decurrent along the achene margins, the tubercle surface often whitish-waxy
............ ............ ............ ............ ..26 Clusters usually compact; achene suborbicular to elliptic, averaging 6-7 transverse ridges; most tubercle bases flat across the achene summit, not decurrent, the tubercle surface usually dark, not waxy
............ ............ ............ ............ 25 Cluster branches stiff; bristles < 1/3 to ¾ (-1) as long as the achene; achene tumid above, often somewhat compressed below, 1.0-1.9 mm long, 1.0-1.7 mm wide; [section Globulares].
............ ............ ............ ............ ....27 Achenes 1.5-1.9 mm long, 1.4-1.7 mm wide, the transverse ridging faint to absent; tubercle grayish-tan to bony white, and buttressed at the base by a thick bony-white rim; leaves to 3 mm wide
............ ............ ............ ............ ....27 Achenes 1.0-1.9 mm long, 1.0-1.7 mm wide, the transverse ridging evident; tubercle grayish to dark brown, without a bony-white buttress; leaves to 3 or 5 mm wide.
............ ............ ............ ............ ......28 Larger culm leaves to 5 mm wide; achenes (1.2-) 1.4-1.6 (-1.9) mm long, (1.1-) avg. 1.4 (-1.75) mm wide; achene surface alveoli longitudinally narrow; tubercle 0.3-0.7 mm long, base 0.6-1.0 mm wide
............ ............ ............ ............ ......28 Larger culm leaves to 3 mm wide; achenes (1.0-) avg. 1.3 (-1.5) mm long and wide; if achene surface alveoli longitudinally narrow, then tubercle 0.2-0.4 mm long and base 0.5-0.7 mm wide (R. globularis).
............ ............ ............ ............ ........29 Longer bristles ⅓-½ (-¾)× the length of the achene; achene surface alveoli longitudinally narrow (typically 0.02-0.05 mm wide between the longitudinal walls), the latitudinal walls raised into horizontal ridges; tubercle 0.2-0.4 mm long, the base 0.5-0.7 mm wide
............ ............ ............ ............ ........29 Longer bristles ⅔-1× the length of the achene; achene surface alveoli nearly as wide as long (typically 0.05-0.1 mm wide between the longitudinal walls), the latitudinal walls obscurely or not at all raised into horizontal ridges; tubercle 0.35-0.7 mm long, the base 0.7-0.9 mm wide
............ ............ ............ ..........24 Bristles equaling or longer than the tubercle.
............ ............ ............ ............ ..........30 Primary branches of the inflorescence spreading at right angles from the culm, each spikelet or small cluster on slender spreading or reflexed stalks; [section Mixtae]
............ ............ ............ ............ ..........30 Primary branches of the inflorescence ascending.
............ ............ ............ ............ ............ 31 Spikelets 6-9 mm long; [section Mixtae]
............ ............ ............ ............ ............ 31 Spikelets < 5 mm long.
............ ............ ............ ............ ............ ..32 Tubercle 0.4-0.8 mm long, the edges setose or uneven with waxy or crusty irregular protuberances; [section Mixtae].
............ ............ ............ ............ ............ ....33 Achene obovate to suborbicular, 1.2-1.6 mm wide, latitudinal alveoli walls strongly raised into transverse ridges
............ ............ ............ ............ ............ ....33 Achene slenderly obovoid, 0.8-1.0 mm wide, latitudinal alveoli walls weakly or not at all raised into transverse ridges
............ ............ ............ ............ ............ ..32 Tubercle 0.2-0.5 mm long, the edges smooth.
............ ............ ............ ............ ............ ......34 Spikelets 3.5-4 mm long; bristles exceeding the tubercle; achene 1.3-1.5 mm long, 1.2-1.3 mm wide; [section Globulares]
............ ............ ............ ............ ............ ......34 Spikelets 2.5-3 mm long; longer bristles about equaling the tubercle; achene 0.8-1.2 mm long, 0.7-1.2 mm wide; [section Mixtae].
............ ............ ............ ............ ............ ........35 Inflorescence occupying the upper ¼-½ of the culm, the lowest 2-4 nodes barren
............ ............ ............ ............ ............ ........35 Inflorescence occupying ⅔-¾ of the length of the culm, the lowest lateral panicle at the first or second node above the base