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Key to Eleocharis, Key B: spikerushes with culms nodose-septate (bearing complete septae, externally evident); achenes biconvex

Cyperaceae

Eleocharis

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1 Culms < 3 mm in diameter.
© Scott Ward
(c) Kampen, Tony van - CC-BY
  2 Spikelets cylindric, the width the same as the width of the culms; roots (usually) with conspicuous tubers; achenes 2.0-2.5 mm long; tubercles triangular-attenuate; [cultivated waif, GA, potentially elsewhere]
© Scott Ward
© Scott Ward
  2 Spikelets ovoid, the width of the base slightly exceeding the width of the culms; roots without tubers (rhizomes often concealed by culms and roots); achenes 0.8-1.1. mm long; tubercles depressed-pyramidal; [common, widespread native, GA and FL w. to TX]
1 Culms > 5 mm in diameter.
(c) Ward, Scott G
    3 Spikelets narrowly ovoid, wider at the base and tapering to the apex; achene bodies < 1.2 mm long, surface finely reticulate; scales (2-) 2.5-3 mm long, delicate, purplish-brown; [uncommon, c. FL]
© Scott Ward
    3 Spikelets cylindric, the width uniform from base to apex; achene bodies > 1.4 mm long, surface rugulose (or smooth to finely cancellate in E. dulcis); scales (3-) 4.5-7 mm long, leathery (besides margins), pale yellowish-brown (sometimes grayish green in E. dulcis, but often maturing stramineous); [common to intermittent, collectively widespread].
      4 Roots (usually) with conspicuous tubers; achenes 2.0-2.5 mm long, primarily smooth or sometimes finely cancellate (transverse cells obscure, if present), the bristles as long as or exceeding tubercle; [cultivated waif, GA, potentially elsewhere]
      4 Roots lacking conspicuous tubers; achenes 1.4-2.3 mm long, with visible longitudinal ridges (E. interstincta) and/or transversely elongated cells (E. equisetoides, which can sometimes also be mostly smooth but has bristles shorter than achene); [widespread natives].
(c) Ward, Scott G - CC-BY
        5 Achenes 1.8-2.3 mm long; pistillate scales 5.2-7 mm long; achene faces with longitudinal rows of enlarged linear cells separated by obscure longitudinal lines; perianth bristles slender and flexuous, finely spinulose, shorter than to equaling the achene (to 2.5 mm long); culm septae widely (> 10 mm) and ± evenly spaced; [widespread in our area]
(c) Ward, Scott G
        5 Achenes 1.4-1.8 (-2) mm long; pistillate scales (4-) 4.5-5 mm long; achene faces with 20-40 bold transverse-rugulose lines; perianth bristles stiff and stout, coarsely spinulose, exceeding the achene (to 2.9 mm long); culm septae concentrated proximally (below spikelet); [OK, TX, AL, and FL; widespread in c. and s. FL]