Eleocharis subg. Scirpidium
Ann. Bot. Fenn. 27: 114. 1990.
Plants annual or perennial, very rarely with spikelets proliferating, culms never rooting at tips (spikelets very rarely proliferating in Eleocharis reverchonii). Rhizomes present or absent, creeping. Tubers and bulbs (resting buds) absent, or resting buds sometimes present in E. acicularis. Culms 1–40 cm × 0.2–1.2 mm, spongy, transverse septa incomplete. Spikelets ovoid to subcylindric, terete, much wider than their culms, 2–9 mm; rachilla with proximal internodes as long and as thick as internodes in middle of spikelet; proximal scale subtending a flower; floral scales ca. 4–30 per spikelet, spiraled, 1–3.5 mm, with 1 vein or fewer than 10 widely spaced longitudinal veins, membranous. Styles 3-fid. Achenes trigonous to nearly terete, 0.5–1.1 mm, with 9–13 longitudinal rows of fine horizontal ridges (trabeculae) between much more prominent longitudinal ridges and achene angles. Tubercles distinct from achene in color, texture and form, not dorsoventrally greatly compressed.
North America to South America, West Indies, Eurasia, Hawaii, Australia (probably introduced).
Species ca. 12 (7 in the flora).
The three achene angles are very similar to the longitudinal ridges. Plants of subg. Scirpidium without achenes are easily mistaken for plants of 8a3. Eleocharis subg. Eleocharis sect. Parvulae, which may be distinguished by the absence of a flower in the axil of the proximal scale of the spikelet.
Key to the species of Eleocharis subg. Scirpidium
|1||Culms distinctly compressed, to 1.2 mm wide, each side with 1 to few sharp ridges or 1 side smooth, margins usually––and ridges often––minutely serrulate at 10–30X; spikelet scales (2.2–)2.7–3.2 mm.||Eleocharis wolfii|
|1||Culms not or slightly compressed, or if distinctly compressed then each side with 3–6 blunt ridges, to 0.5(–0.7) mm wide, margins and ridges smooth; spikelet scales 0.8–2.5(–3.5) mm.||> 2|
|2||Floral scales 0.8–2 mm, apex narrowly acute to acuminate, mostly slightly recurved; anthers 0.2–0.5 mm; culms 1–7 cm, mostly densely tufted; rhizomes seldom evident.||> 3|
|2||Floral scales 1.5–2.5 mm, apex rounded to acute, not recurved; anthers 0.3–1.5 mm; culms 1–45 cm; rhizomes mostly evident.||> 5|
|3||Achenes 0.4 mm, obpyriform; anthers 0.7–1.2 mm; floral scales lanceolate, folded lengthwise.||Eleocharis brachycarpa|
|3||Achenes 0.5–0.75 mm, obovoid, rarely obpyriform; anthers 0.2–0.5 mm; floral scales ovate to lanceolate, not folded lengthwise.||> 4|
|4||Achenes broadly obovoid to obpyriform, 0.5–0.6 mm, trabeculae 15–20; anthers 0.2–0.3 mm.||Eleocharis cancellata|
|4||Achenes obovoid, (0.55–)0.65–0.75 mm, trabeculae 20–30; anthers (0.2–)0.3– 0.5 mm.||Eleocharis bella|
|5||Anthers 0.3–0.5 mm; culms very spongy, without prominent ridges or angles, 1–12 cm.||Eleocharis radicans|
|5||Anthers 0.5–1.5 mm; culms firm to flaccid, not very spongy, often prominently ridged or angled, 1–45 cm.||> 6|
|6||Achenes 0.5–0.7 mm, trabeculae 20–30; scales 1.5–1.7 mm; culms 0.15–0.3 mm wide.||Eleocharis reverchonii|
|6||Achenes 0.7–1.1 mm, trabeculae 30–60; scales 1.5–2.5(–3.5) mm; culms 0.2– 0.5(–0.7) mm wide.||Eleocharis acicularis|