Coastal Plain Spike Rush

We have seen only one collection of Eleocharis retroflexa from the flora area (Mobile, Alabama, in 1896, US). Other populations are likely in the United States Gulf States. The broad-shouldered, strongly sculptured achenes, trilobed, decurrent tubercles, and basal spikelets are distinctive.

Plants annual, tufted, mat-forming, often stoloniferous, sometimes entirely vegetative; rhizomes absent. Culms erect, ascending or arching, pentagonal, sulcate, 1.5–10 cm × 0.2–0.3 mm [larger], soft. Leaves: distal leaf sheaths persistent or disintegrating, pale brown to green, red-spotted [mostly red-brown], membranous; apex acuminate. Spikelets: basal spikelets usually present, bisexual; often proliferous, ellipsoid or obovoid, laterally compressed, 1.7–3.9 × 1.2–2 mm, apex acute; proximal scale empty or with a flower, deciduous, amplexicaulous, similar to floral scales (sometimes 2.4–2.9 mm); subproximal scale with a flower; floral scales clearly distichous, 2–6 [or more], 4–6 per mm of rachilla, pale brown [marked red-brown], ovate or elliptic, 1.8–2.5 × 0.8–1.4 mm, membranous, apex rounded to obtuse, midribs green, keeled. Flowers: perianth bristles 6, colorless or pale brown, shorter than achenes; spinules not evident at 45X; stamens 3; anthers (0.55–)0.7 mm; styles 3-fid. Achenes stramineous (to cream), obovoid, trigonous or subterete, not compressed, angles prominent, 0.8 × 0.5–0.55 mm, apex not constricted proximal to tubercle, coarsely cancellate or honeycomb-reticulate at 10–15X. Tubercles red-brown, pyramidal, trigonous, proximally clearly to obscurely 3-lobed, lobes decurrent on achene angles, 0.3–0.35 × 0.3–0.4 mm.

Ala.; Mexico; West Indies; Bermuda; Central America; South America; Asia (including Indonesia); Pacific Islands; Australia.

Fruiting summer.

Freshwater ponds, stream banks, marshes, sandy or muddy soils; 0–10m.

Scirpus retroflexus Poiret in J. Lamarck et al., Encycl. 6: 753. 1804; Baeothryon retroflexum A. Dietrich; Chaetocyperus niveus Liebmann; C. polymorphus Lindley & Nees var. depauperatus Nees; C. rugulosus Nees; C. viviparus Liebmann; Cyperus depauperatus Vahl; Eleocharis depauperata Kunth