Tropicos | Name - !!Rhynchospora Vahl

!!Rhynchospora Vahl

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12. Rhynchospora Vahl

(Gale, 1944)

Plants perennial (rarely annual elsewhere) often with rhizomes and/or bulbous-thickened aerial stem bases. Aerial stems few to many per plant, erect to spreading, unbranched below the inflorescence, 3-angled, glabrous. Leaves basal and alternate, few to many, the sheath without a ligule, the leaf blade erect to ascending or sometimes recurved, the margins with minute, sharp teeth, at least in the apical half, glabrous. Inflorescences terminal and usually also axillary, with reduced, erect to spreading, scalelike or leaflike bracts at the branching points, composed of few to many, dense to loose clusters of spikelets arranged in panicles, irregular umbels, or less commonly racemes. Spikelets with the scales several-ranked in an overlapping spiral pattern, the 1–5 lowermost scales empty. Fertile florets usually 1–5 per spikelet, perfect. Perianth bristles mostly 6 (1–20 elsewhere). Stamens (1–)3. Styles enlarged at the base, persisting on the fruit as a prominent, conical or triangular-flattened tubercle differing in color and/or texture from the main body of the fruit and separated from it by a line or constriction. Stigmas 2. Ovaries and fruits naked, without a perigynium (saclike covering). Fruits biconvex in cross-section, variously turgid or flattened. About 225 species, nearly worldwide, but most diverse in tropical regions.

The species of Rhynchospora in Missouri fall into two well-defined groups. The horned rushes, R. corniculata and R. macrostachya, are robust plants with sharply trigonous, bulbous-based stems and large inflorescences of relatively long spikelets. They are usually segregated as section Calyptrostylis (Nees) Pax. The beaked rushes of section Rhynchospora have shorter, more obtusely trigonous stems lacking bulbous-thickened bases and have smaller inflorescences of shorter spikelets.

Species of Rhynchospora are generally considered poor forage for livestock. The tiny, sharp teeth along the leaf margins are composed of silica, and these make the plants relatively unfit for consumption.

Cladium mariscoides (Muhl.) Torr., twig rush, was reported erroneously as occurring in Missouri. It resembles a robust Rhynchospora or Scirpus. For further discussion, see the treatment of Scirpus.

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1	Leaf blades (6–)8–20 mm wide; spikelets 15–25 mm long; fruits with the main body 3.5–5.5 mm long, the tubercle 13–22 mm long	(2)
+	Leaf blades 0.2–4.0 mm wide; spikelets 2.5–7.0 mm long; fruits with the main body 1.2–2.8 mm long, the tubercle 0.3–1.6 mm long	(3)

2 (1)	Perianth bristles (5)6, 11–14 mm long, all about the same length and longer than the mature fruits	6 Rhynchospora macrostachya
+	Perianth bristles usually 5(3–6), 2–4 mm long, unequal lengths and shorter than the mature fruits (do not confuse the bristles with filaments of the stamens, which are smooth-margined and not expanded at the base)	3 Rhynchospora corniculata

3 (1)	Perianth bristles with downwardly pointing barbs; main body of the fruits narrowly elliptic to narrowly obovate in outline, the tubercle narrowly triangular-attenuate, about as long as the main body of the fruit	(4)
+	Perianth bristles with upwardly pointing barbs or rarely smooth; main body of the fruits broadly elliptic to broadly obovate or broadly ovate in outline, the tubercle broadly triangular or depressed-conical, much shorter than the main body of the fruit	(5)

4 (3)	Leaf blades 0.2–0.4 mm wide, hairlike, the margins inrolled; main body of fruits uniformly brown at maturity, the surface patterned with fine, wavy, horizontal lines, sometimes appearing finely wrinkled	1 Rhynchospora capillacea
+	Leaf blades 0.5–3.5 mm wide, flat; main body of fruits brown with conspicuously pale margins, the surface smooth	2 Rhynchospora capitellata

5 (3)	Main body of the fruits 1.2–1.5 mm long, the surface appearing horizontally wrinkled or ridged, with a secondary, fine pattern of vertical lines between the wrinkles, brown	4 Rhynchospora globularis var. recognita
+	Main body of the fruits 1.5–1.8 mm long, the surface appearing honeycombed with a fine network of ridges and pits that are longer than to about as long as wide, reddish brown to black	5 Rhynchospora harveyi