7d. SCHOENOPLECTUS (Reichenbach) Palla sect. SUPINI (Chermezon) J. Raynal, Adansonia, n.s. 16: 130. 1976.
Scirpus Linnaeus sect. Supini Chermezon, Arch. Bot. Mém. 3: 193. 1929
Plants annual or perennial, cespitose; rhizomes inconspicuous, very short, firm. Culms 0.5–1.5 mm wide. Leaves basal and cauline [all basal]. Inflorescences capitate or of 1 spikelet or with 1–2 branches [sometimes many branched]. Spikelets: scales with single midrib (sometimes with a few faint veins on flanks), apex entire, mucronate or short-awned. Flowers: perianth absent from spikelet flowers [present, Australian S. dissachanthus]; amphicarpic flowers present in some plants of all species. Achenes plane or biconvex, sometimes trigonous, with prominent transverse, wavy, often acute ridges [or sometimes smooth].
Species ca. 22 (3 in the flora): North America, South America (Argentina), Eurasia, Africa (including Madagascar), Indian Ocean islands, Australia.
Plants of this section grow mostly in Africa and Madagascar (J. Raynal 1976).
Schoenoplectus sect. Supini has been confused with sect. Actaeogeton. It can be distinguished by the lack of perianth in the spikelet flowers, the frequent occurrence of amphicarpy, and a cauline leaf in North American species (S. G. Smith and E. Hayasaka 2001, 2002). A perianth in amphicarpic flowers in sect. Supini (in five species in Africa, including S. erectus) was reported by J. Browning (1992), and subsequently perianth bristles were observed in amphicarpic flowers of all three species in North America (S. Galen Smith, pers. obs.). In some species in sect. Supini, including those in North America, many involucral bracts subtend flowers and apparently intergrade with enlarged scales at the spikelet bases. The widths of the strongly 3-dimensional, boat-shaped scales given here were measured on unflattened scales; the widths given by A. E. Schuyler (1969) are mostly much wider and apparently measured on flattened scales.