Rhynchospora nivea
Rhynchospora chalarocephala
showy whitetop
loosehead beaksedge
erect to spreading-ascending, leafybased, trigonous or compressed, ribbed.
erect to ascending-arching, slender, nearly terete, multiribbed.
exceeded by scape;
blades narrowly linear to filiform, 0.2–2 mm wide, 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 3–7, widely spaced, clusters loosely turbinate to hemispheric, to 1.3 cm wide.
white, ovoid, 5–7 mm;
fertile scales several, boat-shaped, 2.5–3.5 mm, keel curved, not sharp.
brown to pale red-brown, lance-fusiform, 3–5.5 mm;
fertile scales elliptic, 2.5–4 mm, acute, midrib short-excurrent.
perianth absent.
perianth bristles 6, ± equaling tubercle.
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 per spikelet, (2.5–)2.7–3.3(–3.5) mm, body pale brown with yellowish center, ± broadly oblong-obovoid distal to stipe, lenticular, 1.5–2 × 0.8–1 mm;
tubercle narrowly triangularsubulate, (1–)1.2–1.5(–2) mm, less than 0.5 mm wide at base.
leaves exceeded by culm;
blades flat, linear, 1–2 mm wide, apex tapering, trigonous.
Rhynchospora nivea
Rhynchospora chalarocephala
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.)
Some specimens of Rhynchospora chalarocephala are very difficult to distinguish from R. microcephala, and unquestionably intergrades occur in peninsular Florida and the Gulf southern coastal plain. Rhynchospora chalarocephala tends to have longer, paler, narrower spikelets in looser clusters; the dilated part of the fruit body has a narrower, more oblong outline; and the tubercle is both narrower with a narrower base and longer (mostly 1–1.5 mm versus 0.9–1.2 mm in R. micro-cephala). Most material is easily sorted because R. chalarocephala has paler spikelets in turbinate to hemispheric clusters; the dark brown spikelets of R. microcephala are in globose heads.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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