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Eleocharis
See list of 27 species in this genusIn the following key, achene length does not include the apical tubercle, and stem widths are for dried, pressed specimens. Also, the dimensions of tubercles on freshly collected specimens can be very different from those on dried material, particularly during the early stages of fruit maturation. Therefore, fruits should be dry prior to measurement of tubercles. Reference: Smith et al. (2002).
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1a. Floral scales longitudinally striate, usually with red-brown to purple spots on the adaxial (i.e., inner) surface; spikes hardly, if at all, thicker than the stem at ⅔ height
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2a. Reproductive stems triangular in cross-section; rhizomes often producing flaccid, capillary, leaf-like stems; spikes 4- to 8-flowered, 7–20 (–25) mm tall; floral scales with a keeled midrib
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2b. Reproductive stems terete or quadrangular in cross-section; rhizomes not producing capillary stems; spikes many-flowered, 15–50 (–60) mm tall; floral scales with an obscure central keel
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3a. Reproductive stems both terete and septate
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3b. Reproductive stems quadrangular, lacking septa
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1b. Floral scales without fine longitudinal striae, lacking spots on the adaxial surface; spikes noticeably thicker than upper portion of stem
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4a. Tubercle not obviously differentiated from and nearly confluent with the summit of the achene, forming a stylar beak [Fig. 117]
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5a. Stems 1–2 mm thick at midpoint, (15–) 40–100 cm tall, often some arching and rooting at the tip; spikes mostly 10- to 20-flowered; caudex short and thick, the plants lacking rhizomes
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5b. Stems up to 1 mm thick at midpoint, 3–40 cm tall, none arching and tip-rooting; spikes mostly 2- to 9-flowered; rhizomes present, long and slender, often terminated by a thickened bud
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6a. Achenes 1.9–2.6 mm long; floral scales 2.5–5 mm long; plants primarily of high-pH wetlands and shores
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6b. Achenes 0.9–1.3 mm long; floral scales 1.5–2 (–2.5) mm long; plants primarily of brackish water flats and shores
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4b. Tubercle obviously differentiated from the achene, set apart by differences in color and/or texture [Figs. 111,112,118]
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7a. Achenes gray at maturity, longitudinally striate, with numerous, fine horizontal cross-lines, ca. 2 times as tall as wide [Fig. 111]; floral scales all bearing flowers, arranged in 2 or 3 vertical ranks
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7b. Achenes not combining the above characteristics (i.e., lacking conspicuous longitudinal striae, usually no more than 1.5 times as tall as wide); floral scales not all subtending flowers, usually the basal 1 (or more) empty, arranged in more than 3 vertical ranks
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8a. Achenes planoconvex to biconvex in cross-section; styles bifid (trifid in E. obtusa)
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9a. Base of tubercles with a slight to prominent constriction at the junction of achene [Fig. 116]; plants perennial, with rhizomes (these often difficult to detect in E. flavescens)
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10a. Stems cespitose, with slender, often inconspicuous, rhizomes; leaf sheaths prolonged at summit into a white, scarious tip; anthers 0.7–1 mm long
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10b. Stems occurring singly or a few together, produced along obvious, firm rhizomes; leaf sheaths firm at summit; anthers 1–3 mm long
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11a. Glumes 2 (rarely 3), lanceolate to triangular, each sheathing ± ½ (up to ⅔) of the base of the spike
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11b. Glume solitary, suborbicular, nearly encircling the base of the spike and sheathing ¾ or more of it
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12a. Achenes minutely but visibly and regularly patterened with cellular reticulations [Fig. 113]; tubercles 0.15–0.3 (–0.5) mm tall; leaf sheaths firm, many with a thickened, coriaceous collar at the summit
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12b. Achenes obscurely patterened, nearly smooth [Fig. 116]; tubercles 0.35–0.8 mm tall; leaf sheaths herbaceous at summit, not or only slightly thickened
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13a. Floral scales subcoriaceous, lustrous, the lower and middle ones of the spikelet 3–5 mm long; spikes with (5–) 10–20 (–30) flowers; plants of tidal and/or saline-influenced shores
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13b. Floral scales membranaceous, not or scarcely lustrous, the lower and middle ones of the spikelet 1.8–3 mm long; spikes with (15–) 20–40 (–50) flowers; plants primarily of non-tidal wetlands and shores
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9b. Base of tubercle not constricted at junction of achene; plants annual, with fibrous roots [Fig. 112]
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14a. Perianth bristles numbering 5–7 per achene, retrorsely barbellate, exceeding the length of the achene body (and often the tubercle as well)
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15a. Tubercles 0.5–0.9 mm wide, 0.65–0.97 times as wide as the achene; flowers usually with 3 stamens
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16a. Styles usually trifid; tubercles 0.2–0.4 mm tall, 0.29–0.67 times as tall as wide; perianth bristles usually exceeding tubercle in length; spikes commonly ovoid (in part)
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16b. Styles bifid or sometimes trifid; tubercles 0.12–0.23 mm tall, 0.1–0.38 times as tall as wide; perianth bristles often not exceeding the tubercle; spikes commonly ellipsoid to ellipsoid-cylindric (in part)
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15b. Tubercles 0.35–0.5 mm wide, 0.46–0.72 times as wide as the achene; flowers usually with 2 stamens
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14b. Perianth bristles lacking or, if present, numbering 2–4, smooth, and shorter than the achene body [Fig. 112]
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17a. Tubercles 0.46–0.83 mm wide, 0.65–0.97 times the width of the achene; flowers with usually 3 stamens
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18a. Tubercles 0.12–0.23 mm tall, 0.1–0.38 times as tall as wide; styles bifid or sometimes trifid; plants occurring on lake borders and in pools and seepages (in part)
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18b. Tubercles 0.2–0.4 mm tall, 0.29–0.67 times as tall as wide; styles trifid or sometimes bifid; plants occurring on river shores and lake borders (in part)
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17b. Tubercles 0.24–0.45 mm wide, 0.46–0.68 times the width of the achene; flowers with 2 stamens
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19a. Floral scales acute and somewhat keeled at the apex; tubercles mostly 0.1–0.2 mm tall; perianth bristles absent or up to 0.15 mm long; plants occurring on sand shores that are not or only minimally tidal
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19b. Floral scales rounded and not keeled at the apex; tubercles mostly 0.2–0.3 mm tall [Fig. 112]; perianth bristles absent or up to 0.45 mm long; plants occurring on sand, silt, or mud shores that are usually fresh-tidal (rarely on shores of impounded lakes)
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8b. Achenes bluntly triangular to terete in cross-section; styles trifid
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20a. Stems cespitose, arising from fibrous roots or a caudex (i.e., rhizomes lacking); plants annual (perennial in E. melanocarpa)
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21a. Tubercle as wide as the achene; stems compressed
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22a. Achenes dark brown to nearly black at maturity, smooth on the surface, with a low tubercle much shorter than the achene body [Fig. 115]; perianth bristles shorter than the achene; plants perennial from a stout caudex; stems infrequently arching and rooting or proliferating from tip
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22b. Achenes brown to brown-green at matuity, with regular, conspicuous excavations on the surface (i.e., resembling honeycomb), with a large tubercle ± as tall as the achene body; perianth bristles longer than the achene; plants annual from fibrous roots; stems upright, not tip rooting
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21b. Tubercle clearly narrower than achene; stems terete to capillary, but not obviously compressed
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23a. Achenes green to brown-green, 1.2–1.5 mm long, topped with an elongate, cone-shaped tubercle; floral scales 1.7–2.5 mm long; longer perianth bristles exceeding combined length of achene and tubercle
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23b. Achenes pale, nearly white, 0.5–1 mm long, topped by a minute, depressed-conic tubercle; floral scales 1–1.5 mm long; longer perianth bristles up to as long as the combined length of the achene and tubercle
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20b. Stems produced singly or a few together along an obvious rhizome; plants perennial
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24a. Achenes with prominent keel-like angles; rhizomes firm, 3–6 mm thick
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24b. Achenes rounded on the angles, without keels; rhizomes flexible, 0.5–3 mm thick
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25a. Stems conspicuously compressed, 2–5 times as wide as thick, 0.5–1.8 mm wide; apical portion of floral scales in the basal portion of the spike often bifid, with a hyaline, colorless region 0.6–1.2 mm long that is longer than wide
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25b. Stems angled to somewhat compressed, 1–2 (–3) times as wide as thick, 0.15–0.8 mm wide; apical portion of floral scales in the basal portion of the spike entire to emarginate, with a hyaline, colorless region that is up to 0.7 mm long and is wider than long to as long as wide
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26a. Summit of leaf sheath lacking a tooth-like lobe; achenes 0.6–0.7 ×0.45–0.55 mm; anthers 0.3–0.7 mm long; floral scales 1–1.4 mm long; rhizomes 0.5–1 mm thick
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26b. Summit of leaf sheath usually with a tooth-like lobe; achenes 0.7–1.2 ×0.6–0.9 mm; anthers 1.5–2 mm long; floral scales 1.5–3.5 mm long; rhizomes 1–3 mm thick
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27a. Achenes 1.1–1.5 ×0.95–1.25 mm, finely patterned with cellular reticulations; stems 0.5–1.5 mm thick at the midpoint
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27b. Achenes 0.6–1.2 ×0.45–0.9 mm, regularly patterned with conspicuous excavations (i.e., resembling honeycomb); stems 0.2–0.8 mm thick at the midpoint
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28a. Stems usually 6- to 8-angled; achenes yellow to orange-yellow, somewhat persistent after the falling of the floral scales, with 12–20 horizontal ridges through the length of the achene [Fig. 114]
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28b. Stems 4- or 5-angled; achenes green to brown-green (rarely yellow), deciduous with the falling scales, with 6–10 (–14) horizontal ridges through the length of the achene
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