Scirpus atrocinctus
Scirpus divaricatus
black-girdle bulrush, black-girdle woolsedge, common woolly sedge, scirpe à ceinture noire, wool-grass
spreading bulrush
fertile ones upright or nearly so;
nodes without axillary bulblets.
fertile ones lax, reclining, inflorescences lopping over to (or nearly to) ground;
nodes frequently with axillary bulblets.
4–7 per culm;
sheaths of proximal leaves brown;
proximal sheaths and blades with septa few to many, conspicuous or inconspicuous;
blades 25–63 cm × 3–6 mm.
10–18 per culm;
proximal leaf sheaths green or brownish;
proximal sheaths and blades with septa few, inconspicuous;
blades 16–55 cm × 4–8 mm.
terminal;
rays ascending or sometimes spreading, scabrous throughout or main branches smooth proximally, rays rarely with axillary bulblets;
bases of involucral bracts usually blackish, not glutinous.
terminal;
rays divergent, proximal rays smooth, pedicels and distal rays scabrous, rays often bearing axillary bulblets;
bases of involucral bracts green or brownish, not glutinous.
in open cymes, central spikelet of each cyme sessile, others usually pedicellate, spikelets ovoid or ellipsoid, 4–7 × 2–2.7 mm;
scales usually blackish, at least distally, oblong-ovate or oblong-elliptic, 1.3–1.8 mm, apex rounded or very weakly apiculate, apiculus (if present) to 0.05 mm.
in open cymes, central spikelet of each cyme sessile, others long-pedicellate, spikelets cylindric to narrowly ovoid, 4–14 × 1–2 mm;
scales light brown to reddish with broad green midribs, broadly ovate or elliptic, 1.2–1.8 mm, apex rounded to obtuse, apiculate, or sometimes short-mucronate, apiculus or mucro (if present) to 0.1 mm.
perianth bristles persistent, 6, slender, contorted, much longer than achene, smooth, projecting beyond scales, mature inflorescence appearing woolly;
styles 3-fid.
perianth bristles persistent, 6, stout, contorted, equaling or longer than achene, not projecting beyond it, with delicate, round-tipped, retrorse teeth in distal 1/2, enclosed within scales;
styles 3-fid.
whitish, elliptic or obovate in outline, plumply trigonous or plano-convex, 0.7– 0.9 × 0.4–0.5 mm.
off-white to yellowish brown, elliptic-obovate in outline, strongly trigonous with very strong angles and concave sides, 0.8–1 × 0.6–0.8 mm.
= 68.
= 28.
Scirpus atrocinctus
Scirpus divaricatus
Scirpus atrocinctus differs from S. pedicellatus by having more intense pigmentation in its inflorescence, both in the scales and the bases of the involucral bracts. Scales of S. atrocinctus are usually distinctly blackened, at least distally, and those of S. pedicellatus show either no black pigment at all or indistinct blackening beside the distal part of the midrib. Brown streaking throughout the scale is usually prominent in both species. The bases of the involucral bracts are almost always solid black in S. atrocinctus and reddish brown, brownish, or merely tinged or bordered with black in S. pedicellatus. The scales of S. pedicellatus also differ from those of S. atrocinctus in usually having a short mucro. All of these characteristics are variable. The two species are usually quite distinct when they grow close together, and they are not known to hybridize with each other (although each species hybridizes with S. cyperinus). It is often difficult to identify isolated herbarium specimens with confidence.
Scirpus atrocinctus often hybridizes with S. cyperinus and forms hybrid swarms. The type of S. pedicellatus forma viviparus F. G. Bernard appears to be S. atrocinctus × cyperinus.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
The inflorescence of Scirpus divaricatus is very large and open. As in related species, the central spikelet of each cyme is sessile, and the others are long-pedicellate. The cymes often consist of only two spikelets in which the sessile, terminal spikelet may appear lateral.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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