8a1c. ELEOCHARIS R. Brown (subg. ELEOCHARIS sect. ELEOCHARIS) ser. ROSTELLATAE S. González & P. M. Peterson, Taxon. 46: 440. 1997.
Plants perennial, stoloniferous, with some culms arching or decumbent and rooting at tips. Rhizomes caudexlike, concealed by crowded culms, ascending or partly horizontal, very short, 3 mm thick, internodes crowded. Culms compressed, 0.3–2 mm thick. Leaves: distal leaf sheaths persistent, papery, apex obtuse to subacute, tooth absent. Spikelets terete, basal spikelets absent; floral scales spiraled, membranous to cartilaginous; styles 3-fid, or 3-fid and 2-fid. Achenes medium to dark brown, beak paler, plano-convex to trigonous or biconvex, usually distally narrowed into a distinct beak, rugulose at 10X or smooth or finely reticulate at 10–30X. Tubercles usually obscure or absent, often merging with achene apex in color, texture, and form.
Species 2 (1 in the flora): North America, Mexico, West Indies, South America.
H. K. Svenson (1957) grouped Eleocharis rostellata with ser. Parvulae and subg. Zinserlingia in ser. Pauciflorae Svenson. Most authors interpret the pale colored achene beak in ser. Rostellatae as a tubercle. However, because the surface textures of the beak and achene are very similar and intergrade, the beak is here interpreted as part of the achene and the apical darker style base remnant often present is interpreted as the tubercle. Achene lengths given here are longer than given by many authors and tubercle lengths are shorter.