Flora of North America species comparison

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Eleocharis tenuis

Eleocharis decumbens

dog's hair, slender spike-rush, slender spikesedge

decumbent spikerush
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. Plants perennial, densely tufted; rhizomes often hidden by culms and roots, fairly long, 3–4 mm thick, hard, cortex persistent, longer internodes from very short to 5 mm, scales usually clearly evident, disintegrating to fibers, 20–25 mm, papery.
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.

terete, often with 10–18 blunt ridges when dry, 10–50 cm × 0.3–2 mm, firm to rigid, spongy.
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.

distal leaf sheaths persistent, not splitting, proximally brown or reddish, distally stramineous, brown, reddish or green, often inflated, papery, apex mostly dark red-brown, subtruncate to obtuse, often callose, tooth absent.
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.

ovoid, 3–8 × 2–2.5 mm, apex acute;

proximal scale amplexicaulous, entire;

subproximal scale empty or with flower;

floral scales appressed in fruit, 10–20, 3 per mm of rachilla, orange-brown, midrib regions often greenish, ovate, 3–3.5 × 1.5 mm, apex entire, acute, often carinate in distal part of spikelet.
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.

perianth bristles 6, stramineous, stout, nearly equal, mostly equaling or exceeding tubercle, (0.5–)1–2.2 mm, prominently retrorsely spinulose;

stamens 3(?);

anthers dark yellow to stramineous, 1.2–1.5;

styles 3-fid.
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.

falling with scales, dark brown, obpyriform, nearly eqilaterally- to greatly compressed-trigonous, angles slightly prominent, 1–1.3 × 0.75–0.9 mm, neck absent or short, finely rugulose at 20X with more than 20 horizontal ridges in vertical series, or reticulate or cancellate at 20–30X.
Tubercles

brown, pyramidal and to as high as wide to greatly depressed-apiculate, often rudimentary, 0.05–0.3 × 0.25–0.4 mm.

well developed, whitish, pyramidal, as high as wide to much lower than wide, 0.2–0.6 × 0.4–0.7 mm.

Eleocharis tenuis

Eleocharis decumbens
Phenology Fruiting summer–fall.
Habitat Wet fresh meadows, seeps, and lakeshores, in interior montane conifer forests and alpine zones
Elevation 700–3500 m (2300–11500 ft)
Distribution
from FNA
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
[WildflowerSearch map]
[BONAP county map]
from FNA
CA; OR
[BONAP county map]
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.)

Eleocharis decumbens is known only from Shasta and Tulare counties in California.

Although Eleocharis decumbens has long been ignored or treated as a variety of E. montevidensis, it clearly is a very distinct species, from which it differs especially in its thick rhizomes with fibrous scales and its acute floral scales.

Specimens of Eleocharis decumbens without rhizomes or achenes are easily confused with the apparently closely related E. bolanderi, which often may be distinguished by culms no more than 0.5 mm wide and spikelets with scales no more than 3 mm long. The tubercles of E. decumbens are usually well differentiated from the achenes and about as high as wide; the tubercles of E. bolanderi are often poorly developed and much lower than wide. Three collections from Jackson and Klamath counties in Oregon, lack achenes but are probably E. decumbens.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Culms sharply angled, usually deeply sulcate, to 0.8 mm wide; some or all culms with distal leaf sheaths with stout apical tooth to 0.4–0.6(–0.9) mm; achenes usually lemon yellow to dark yellow, with 10–14 obscure to clearly evident depressions in each vertical series; tubercles mostly greatly depressed, much lower than wide.
var. pseudoptera
1. Culms bluntly angled to smooth, seldom deeply sulcate, to 0.5 mm wide; distal leaf sheaths without tooth or with slender apical tooth to 0.2 mm; achenes usually yellow to green or brown, with 6–12 depressions in each vertical series; tubercles as high as wide to greatly depressed.
→ 2
2. Rhizomes 0.4–1 mm thick, longer internodes (2–)5–10 mm; tubercles as high as wide, sometimes greatly depressed; achenes finely rugulose and cancellate.
var. tenuis
2. Rhizomes (1–)1.5–2 mm thick, longer internodes 2 mm; tubercles greatly depressed, rarely pyramidal; achenes coarsely (to finely) rugose at 10X and usually cancellate at 10–20X.
var. verrucosa
Source FNA vol. 23, p. 86. FNA vol. 23.
Parent taxa Cyperaceae > Eleocharis > subg. Eleocharis > sect. Eleocharis > ser. Eleocharis Cyperaceae > Eleocharis > subg. Eleocharis > sect. Eleocharis > ser. Eleocharis
Sibling taxa
E. acicularis, E. aestuum, E. albida, E. ambigens, E. atropurpurea, E. baldwinii, E. bella, E. bernardina, E. bicolor, E. bifida, E. bolanderi, E. brachycarpa, E. brittonii, E. cancellata, E. cellulosa, E. coloradoensis, E. compressa, E. cylindrica, E. decumbens, E. diandra, E. elliptica, E. elongata, E. engelmannii, E. equisetoides, E. erythropoda, E. fallax, E. flavescens, E. geniculata, E. intermedia, E. interstincta, E. kamtschatica, E. lanceolata, E. macrostachya, E. mamillata, E. melanocarpa, E. microcarpa, E. minima, E. montana, E. montevidensis, E. nana, E. nigrescens, E. nitida, E. obtusa, E. obtusetrigona, E. occulta, E. ovata, E. pachycarpa, E. palustris, E. parishii, E. parvula, E. quadrangulata, E. quinqueflora, E. radicans, E. ravenelii, E. retroflexa, E. reverchonii, E. robbinsii, E. rostellata, E. suksdorfiana, E. torticulmis, E. tortilis, E. tricostata, E. tuberculosa, E. uniglumis, E. vivipara, E. wolfii
E. acicularis, E. aestuum, E. albida, E. ambigens, E. atropurpurea, E. baldwinii, E. bella, E. bernardina, E. bicolor, E. bifida, E. bolanderi, E. brachycarpa, E. brittonii, E. cancellata, E. cellulosa, E. coloradoensis, E. compressa, E. cylindrica, E. diandra, E. elliptica, E. elongata, E. engelmannii, E. equisetoides, E. erythropoda, E. fallax, E. flavescens, E. geniculata, E. intermedia, E. interstincta, E. kamtschatica, E. lanceolata, E. macrostachya, E. mamillata, E. melanocarpa, E. microcarpa, E. minima, E. montana, E. montevidensis, E. nana, E. nigrescens, E. nitida, E. obtusa, E. obtusetrigona, E. occulta, E. ovata, E. pachycarpa, E. palustris, E. parishii, E. parvula, E. quadrangulata, E. quinqueflora, E. radicans, E. ravenelii, E. retroflexa, E. reverchonii, E. robbinsii, E. rostellata, E. suksdorfiana, E. tenuis, E. torticulmis, E. tortilis, E. tricostata, E. tuberculosa, E. uniglumis, E. vivipara, E. wolfii
Subordinate taxa
E. tenuis var. pseudoptera, E. tenuis var. tenuis, E. tenuis var. verrucosa
Synonyms Scirpus tenuis E. montevidensis var. decumbens
Name authority (Willdenow) Schultes: Mant. 2: 89. (1824) C. B. Clarke: Bull. Misc. Inform., addit. ser. 8: 23. (1908)
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Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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