12. Rhynchospora Vahl
(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.
(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.