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Published In: Prodromus Florae Novae Hollandiae 1: 224. 1810. (Prodr.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 9/1/2009)
Acceptance : Accepted
 

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6. Eleocharis R. Br. (spike rush)

Plants annual or perennial with rhizomes. Aerial stems few to many per plant, erect to ascending, unbranched, circular to ellipsoid or flattened, less commonly 3–4-angled, glabrous. Leaves reduced to 1–4 bladeless sheaths near the stem bases, the upper edges truncate or oblique, reddish purple, green, or white-membranous. Inflorescences consisting of a single, terminal spikelet, not subtended by bracts. Spikelets with several to numerous florets, the scales several-ranked in an overlapping spiral pattern (rarely 2-ranked elsewhere), the lowermost few scales often empty. Florets perfect. Perianth bristles mostly 6, less commonly fewer or more, or absent. Stamens 1–3. Styles enlarged at the base, persisting on the fruit as a prominent, conical or triangular-flattened tubercle differing in texture and/or color from the main body of the fruit and separated from it by a line or constriction, or rarely undifferentiated and appearing as a stylar beak. Stigmas 2 or 3. Ovaries and fruits naked, without a perigynium (saclike covering). Fruits biconvex or 3-angled, sometimes nearly circular in cross-section. One hundred fifty to 200 species, nearly worldwide.

Although the spike rushes are easily recognized as a genus, species determinations are made difficult by the great overall morphological similarities among species in some complexes and by the relatively simple inflorescence structure of the genus. To identify most Missouri species, it is necessary to note details of the fruits as well as the shapes of the spikelet scales. Care also must be taken in excavating rootstocks of specimens, as the thin rhizomes of some species are easily broken and lost.

 

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1 Aerial stems septate (with noticeable cross-lines at regular intervals) 4 Eleocharis equisetoides
+ Aerial stems not septate (sometimes with irregularly spaced cross-lines in E. palustris) (2)
2 (1) Aerial stems sharply (3–)4-angled, 2–6 mm wide; spikelets about as wide as the stems 10 Eleocharis quadrangulata
+ Aerial stems cylindrical, flattened, or if angled then only 0.5–1 mm wide (3)
3 (2) Fruits tapered to a short stylar beak that is not clearly differentiated from the main body of the fruit in texture or color 9 Eleocharis parvula
+ Fruits with a well-differentiated tubercle that is different in texture and/or color from the body of the fruit and separated from it by a line or constriction (4)
4 (3) Stigmas mostly 2; fruits biconvex, sometimes nearly circular in cross-section (rarely a few 3-angled fruits may be produced in plants of E. ovata that otherwise have only biconvex fruits) (5)
+ Stigmas 3; fruits 3-angled, sometimes bluntly so (9)
5 (4) Mature fruits dark reddish black to black at maturity 2 Eleocharis atropurpurea
+ Mature fruits yellowish brown to brown (6)
6 (5) Plants tufted annuals, lacking rhizomes (7)
+ Plants perennials, with rhizomes (8)
7 (6) Spikelet scales pointed at the tip; spikelets lanceolate in outline, mostly pointed at the tip 6 Eleocharis lanceolata
+ Spikelet scales rounded or blunt at the tip; spikelets mostly oblong to ovate in outline, rounded at the tip or, if bluntly pointed, then not tapered 7 Eleocharis ovata
8 (6) Base of the spikelet with a single sterile scale, this completely encircling the stem; spikelet scales ovate to broadly ovate, the tips rounded to bluntly pointed; fruits dark brown at maturity, the tubercle 0.2–0.4 mm long 5 Eleocharis erythropoda
+ Base of the spikelet with 2–3 sterile scales, these not individually encircling the stem; spikelet scales narrowly ovate to lanceolate, the tips mostly long-tapered, sharply pointed; fruits yellow to brown at maturity, the tubercle 0.4–0.7 mm long 8 Eleocharis palustris
9 (4) Aerial stems strongly flattened (10)
+ Aerial stems circular in cross-section or 4–5-angled (11)
10 (9) Surface of the fruits with 6–10 longitudinal ridges with numerous fine cross-lines between them, white (rarely pale gray or light tan), shiny; rhizomes slender, hairlike 12 Eleocharis wolfii
+ Surface of the fruits finely roughened or honeycombed with a fine network of ridges and pits, lacking longitudinal ribs, yellow to brown; rhizomes stout 3 Eleocharis compressa
11 (9) Surface of the fruits with 10–18 longitudinal ridges with numerous fine cross-lines between them, white (rarely pale gray or light tan); rhizomes slender, hairlike 1 Eleocharis acicularis
+ Surface of the fruits honeycombed with a fine network of ridges and pits, lacking longitudinal ribs, light yellow, turning olive green at maturity; rhizomes thicker, 1–3 mm in diameter 12 Eleocharis verrucosa
 
 
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