6. Eleocharis R. Br. (spike rush)

Plants annual or perennial with rhizomes. Aerial stems few to many per plant, erect to ascending, unbranched, circular to ellipsoid or flattened, less commonly 3–4-angled, glabrous. Leaves reduced to 1–4 bladeless sheaths near the stem bases, the upper edges truncate or oblique, reddish purple, green, or white-membranous. Inflorescences consisting of a single, terminal spikelet, not subtended by bracts. Spikelets with several to numerous florets, the scales several-ranked in an overlapping spiral pattern (rarely 2-ranked elsewhere), the lowermost few scales often empty. Florets perfect. Perianth bristles mostly 6, less commonly fewer or more, or absent. Stamens 1–3. Styles enlarged at the base, persisting on the fruit as a prominent, conical or triangular-flattened tubercle differing in texture and/or color from the main body of the fruit and separated from it by a line or constriction, or rarely undifferentiated and appearing as a stylar beak. Stigmas 2 or 3. Ovaries and fruits naked, without a perigynium (saclike covering). Fruits biconvex or 3-angled, sometimes nearly circular in cross-section. One hundred fifty to 200 species, nearly worldwide.

Although the spike rushes are easily recognized as a genus, species determinations are made difficult by the great overall morphological similarities among species in some complexes and by the relatively simple inflorescence structure of the genus. To identify most Missouri species, it is necessary to note details of the fruits as well as the shapes of the spikelet scales. Care also must be taken in excavating rootstocks of specimens, as the thin rhizomes of some species are easily broken and lost.