Rhynchospora nivea
Rhynchospora wrightiana
showy whitetop
Wright's beaksedge
erect to spreading-ascending, leafybased, trigonous or compressed, ribbed.
slender, ± filiform, leafy, terete to bluntly trigonous.
exceeded by scape;
blades narrowly linear to filiform, 0.2–2 mm wide, apex tapering, trigonous.
shorter than culm;
blades spreading to ascending, ± filiform, proximally flat, 0.5–1(–1.5) mm, apex tapering, trigonous.
terminal, solitary, headlike, dense, white, leafyinvolucrate, hemispheric to globose, 0.5–1.5 cm wide;
involucral bracts (0–)1–4, ascending to recurved, green, (0.7–)2–5(–6) cm × 0.2–2 mm.
spikelet clusters 1–3, loose to dense, widely spaced to close together, turbinate to hemispheric; leafy bracts setaceous, mostly exceeding spikelet clusters.
white, ovoid, 5–7 mm;
fertile scales several, boat-shaped, 2.5–3.5 mm, keel curved, not sharp.
dark redbrown, lanceovoid, 2.5–3.5(–4) mm, apex acute;
fertile scales ovate, 2–3.5 mm, apex acute or acuminate, rarely minutely awned.
perianth absent.
bristles 6, of various length, mostly extending from fruit midbody to tubercle base, antrorsely barbellate.
0.8–1 mm;
body yellow to near black, broadly pyriform-obovoid, tumidly lenticular, 0.5–0.8 × 0.5–0.8 mm, margin narrow, flowing into tubercle;
surfaces transversely sharply wavyrugose, ridges bordered by rows of fine, linear, vertical lattices;
tubercle depressedtriangular, lunate-based, shortbeaked 0.2(–0.3) mm, gray-crustaceous.
1–2 per spikelet, (2–)2–2.5 mm;
body brown with pale center, lenticular, broadly ellipsoid, 1.5–1.7 × 1.2–1.3 mm, surfaces nearly smooth or very finely cancellate;
tubercle flat, triangular with short-oblong, blunttipped nose, or triangularsubulate, 0.5–0.8 mm.
Rhynchospora nivea
Rhynchospora wrightiana
Rhynchospora nivea, of the “Dichromena” of North America, is the smallest fruited and most slender and has the fewest and shortest involucral bracts (in some plants the bract is entirely absent). Involucral bracts of R. nivea are almost entirely green.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
The morphologic boundary between Rhynchospora wrightiana and R. fascicularis (particularly morphs of R. fascicularis referred to R. fascicularis var. distans) is difficult, as recent annotations of the material testify. It is best to consider R. wrightiana as a lower, distinctly filiformleaved entity with darker brown, shorter spikelets and shorter fruit. Kükenthal’s concept of R. wrightiana appears to include a considerable amount of R. fascicularis var. distans.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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