Eleocharis tenuis |
Eleocharis |
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dog's hair, slender spike-rush, slender spikesedge |
spike-rush, spikesedge, éléocharide |
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Habit | Plants perennial, mat-forming; rhizomes evident, 0.4–2 mm thick, soft to hard, cortex persistent, longer internodes 2–10 mm, scales persistent or decaying to fibers, 5–10 mm, papery, finely to coarsely fibrous. | Herbs, annual or perennial, usually cespitose, often rhizomatous, sometimes stoloniferous; rhizomes rarely with terminal tubers or bulbs, horizontal and long or ascending and caudexlike. | ||||||||||||||||||||
Culms | terete or usually with 4 or 5(–6) angles, often sulcate; 5–90 cm × 0.2–0.5(–0.8) mm, firm to soft. |
sometimes solitary, terete, 3–5-angled or more, or strongly compressed in cross section, spongy with internal air cavities and incomplete transverse septa or sometimes hollow with complete transverse septa. |
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Leaves | distal leaf sheaths persistent, not splitting, proximally dark red (or yellow-brown), distally green or stramineous or red, membranous, apex often reddish, obtuse to acute, often callose, often with tooth to 0.2(–0.9) mm. |
basal, 2 per culm; ligules absent; blades absent or a mucro or awn (tooth) at apex of sheath, very rarely flattened, to 6 cm. |
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Inflorescences | terminal; spikelet 1; involucral bracts absent, rarely a proximal scale of spikelet resembling short bract. |
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Spikelets | ovoid, 3–6 × 1.5–2 mm, apex obtuse to acute; proximal scale amplexicaulous, apex entire; subproximal scale with flower; floral scales appressed in fruit, 20–60, 5–6 per mm of rachilla, medium to dark brown, midrib region often paler, ovate, 1.5–2.5 × 1 mm, apex rounded (to acute), entire, rarely shallowly notched, carinate in distal part of spikelet. |
scales 4–500 or more, spirally or rarely distichously arranged, each subtending flower or proximal 1–2(–3) empty, stramineous (straw-brown) to medium brown or red brown or blackish brown. |
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Flowers | perianth bristles absent or sometimes 1–3, stramineous to pale brown, slender, to equaling achene, obscurely retrorsely spinulose; stamens 3; anthers brown, 0.8–1.8 mm; styles 3-fid. |
bisexual; perianth of (0–)3–6(–10) bristles, straight or curved, shorter than to 2 times longer than achene, retrorsely (to antrorsely) spinulose or sometimes smooth; stamens 1–3; styles linear, 2–3-fid, base (tubercle) usually persistent, usually enlarged, usually different in appearance from achene. |
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Achenes | falling with or before scales, lemon yellow, dark yellow, medium brown, or green, obpyriform, trigonous, angles evident, sometimes prominent, 0.6–0.9 × 0.45–0.7 mm, finely to coarsely rugulose and usually alveolate (cancellate) at 10–20X, 6–10(–14) sharp horizontal ridges in each vertical series. |
biconvex, plano-convex, or trigonous to subterete. |
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Tubercles | brown, pyramidal and to as high as wide to greatly depressed-apiculate, often rudimentary, 0.05–0.3 × 0.25–0.4 mm. |
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Eleocharis tenuis |
Eleocharis |
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Distribution |
AL; AR; CA; CT; DC; DE; GA; IA; IL; IN; KS; KY; LA; MA; MD; ME; MO; MS; NC; NE; NH; NJ; NY; OH; OK; PA; RI; SC; SD; TN; TX; VA; VT; WI; WV; NB; NS; PE; QC
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Worldwide |
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Discussion | Varieties 3 (3 in the flora). The name Eleocharis capitata (Linneaus) R. Brown was long misapplied to E. tenuis (H. K. Svenson 1939). Although the extremes of the three varieties are very different, intermediates are fairly common. Some plants are intermediate with E. elliptica. Eleocharis tenuis belongs to the E. tenuis complex, which comprises species 16–21 and is restricted to North America, where it is widely distributed except for the Southeast and Southwest. Eleocharis occulta, E. bifida, and E. nitida are very distinct, have little variation, and have relatively restricted ranges; E. tenuis, E. elliptica, and E. compressa are difficult to separate, are highly variable, and have relatively large ranges (see also discussions under E. compressa and E. elliptica). Eleocharis occulta and E. bifida are evidently closely related to E. compressa; they are known only from unglaciated areas south of the limits of Pleistocene glaciation, while E. compressa has a broad range in glaciated regions. The cytotaxonomic study by L. J. Harms (1972) of E. tenuis, E. elliptica, and E. compressa included artificial interspecific and infraspecific hybrids as discussed under those species. Eleocharis tenuis var. pseudoptera might also be treated as E. elliptica var. pseudoptera following L. J. Harms (1972) because it is intermediate between E. tenuis var. tenuis and E. elliptica var. elliptica in most characters except for the 4-angled, usually deeply sulcate culms. It appears to intergrade with E. elliptica. It is placed in E. tenuis because many plants, including an isotype, are more like E. tenuis than E. elliptica; because most plants key more easily to E. tenuis; and to continue the use of the traditional name. The achenes of the holotype (from Lancaster county, Pennsylvania) and some other specimens closely resemble those of E. elliptica but are not obviously persistent after the scales fall. The usually diagnostic tooth on the distal leaf sheath in E. tenuis var. pseudoptera is also characteristic of E. elliptica var. elliptica; but in E. tenuis var. pseudoptera it is more often present and usually longer and stouter than in E. elliptica. The culms of the holotype of E. tenuis var. pseudoptera and many other specimens are 4- to 5-angled, and in some specimens are very irregularly to 6-angled and often rigid and compressed. L. J. Harms (1972) transferred E. tenuis var. pseudoptera to E. elliptica because he counted the same 2n = 38 chromosome number in both E. elliptica and E. tenuis var. pseudoptera and produced artificial E. elliptica × E. tenuis var. pseudoptera hybrids in which meiotic pairing and pollen stainability were very high. A. E. Schuyler (1977) reported 2n = 39 for E. tenuis var. pseudoptera as well as 2n = 34 and 68 for a putative E. tenuis var. tenuis × E. tenuis var. pseudoptera hybrid. Putative hybrids between Eleocharis compressa and E. erythropoda of the E. palustris complex in Ontario have been reported (P. M. Catling and S. G. Hay 1993), and I have observed putative E. compressa × E. erythropoda and E. elliptica × E. erythropoda hybrids in the field in southeastern Wisconsin. It seems possible that introgression from E. erythropoda is responsible for some of the variation of both E. compressa and E. elliptica, especially the frequent presence of some 2-fid styles and lenticular achenes in both species and some (rarely all) entire floral scales in E. compressa (S. G. Smith 2001). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Species ca. 200 (67 in the flora). The name of the genus has sometimes been given as Heleocharis Lestibudois; this is now regarded as an orthographic variant of Eleocharis. Eleocharis dulcis (Burman f.) Trinius ex Henschel is sometimes cultivated for its edible tubers. Some species are weeds in rice fields, mostly extraterritorially. Almost all species are restricted to wetlands, often emergent, and sometimes submerged aquatic. No recent comprehensive worldwide taxonomic treatment of Eleocharis is available. The treatment herein is based mostly on the extensive studies by H. K. Svenson (1929, 1932, 1934, 1937, 1939, 1947, 1957), which were mostly restricted to species of North America. Classification of Eleocharis is unusually difficult because relatively few macroscopic characters are provided by the simple structure characteristic of the genus (only two leaves, basal, without blades or with only rudimentary blades, and unbranched aerial stems, each with a single terminal spikelet and without an involucral bract). Undoubtedly much evolutionary convergence has occurred in most vegetative and reproductive structures (M. S. González-E. and J. A. Tena-F. 2000; E. H. Roalson and E. A. Friar 2000). North American Eleocharis includes some extremely difficult species complexes that need taxonomic revision: (1) The E. palustris complex (species 1–7) is discussed under 1. E. palustris. (2) The E. tenuis complex (species 16–21) is discussed under 21. E. tenuis. (3) The four species (species 57–60) of 8c. Eleocharis subg. Zinserlingia that occur in North America belong to the E. quinqueflora (= E. pauciflora) complex, discussed under subg. Zinserlingia. (4) All six species of 8a2b. E. ser. Ovatae (species 42–47) constitute a complex discussed under ser. Ovatae. The supraspecific classification of Eleocharis used here is that of M. S. González-E. and P. M. Peterson (1997), which was based on a study of most species worldwide. Other recent classifications are based on more or less regional studies (H. K. Svenson 1957; T. V. Egorova 1981; I. Kukkonen 1990). A study using limited DNA data from 30 species (E. H. Roalson and E. A. Friar 2000), mostly from North America, indicates that the following supraspecific taxa are probably monophyletic: 8a2a. ser. Maculosae, 8a2b. ser. Ovatae, and 8d. subg. Limnochloa, whereas the following taxa are probably para- or polyphyletic: 8a1. sect. Eleocharis, 8a1a. ser. Eleocharis, 8a1d. ser. Tenuissimae, and 8a2. sect. Eleogenus. Users of this treatment should be aware of the following: culms that are smooth when fresh are often ridged when dry; culms of pressed specimens are often flattened and must be carefully rehydrated and sectioned to determine the original cross-section shape; culm widths given here are usually for culms pressed flat; floral scale widths are measured on flattened scales or by doubling the width measured on scales folded along the midrib; and achene length does not include the tubercle, which is often included in descriptions published elsewhere. In this treatment, I describe the tubercle (style base) after the achene in consecutive sentences to stress the separate nature of the two structures. Some species, mostly of 8a1d. Eleocharis ser. Tenuissimae, often proliferate from spikelets, often on arching or horizontal culms, especially when growing as submerged or floating aquatics. Because many such plants reproduce entirely asexually and have no normal spikelets or achenes, it is often impossible to identify them to species. The invalid name E. prolifera Torrey has sometimes been used for these plants. Species of ser. Tenuissimae in which the spikelets may be proliferous and which are easily confused with each other are E. baldwinii, E. brittonii, E. microcarpa, E. nana, E. retroflexa, and E. vivipara. Aquatic forms of at least some of those species are very hard to distinguish from Websteria confervoides (Poiret) S. S. Hooper. Other species in which the spikelets often poliferate or the culm tips root are E. pachycarpa of ser. Tenuissimae, E. melanocarpa of 8a1b. ser. Melanocarpae, and E. rostellata of 8a1c. ser. Rostellatae. When submersed, plants of E. acicularis of 8b. subg. Scirpidium and E. elongata and E. robbinsii of 8d. subg. Limnochloa may be entirely vegetative, the latter two species sometimes forming whorls of flaccid stems without spikelets. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Key to the subgenera of Eleocharis
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Source | FNA vol. 23, p. 86. | FNA vol. 23, p. 60. | ||||||||||||||||||||
Parent taxa | Cyperaceae > Eleocharis > subg. Eleocharis > sect. Eleocharis > ser. Eleocharis | Cyperaceae | ||||||||||||||||||||
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Synonyms | Scirpus tenuis | Scirpus unranked E. | ||||||||||||||||||||
Name authority | (Willdenow) Schultes: Mant. 2: 89. (1824) | R. Brown: Prodr., 224. (1810) | ||||||||||||||||||||
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