Eleocharis intermedia
Eleocharis ambigens
Matted spikerush, mudflat spikesedge, éléocharide intermédiaire
ambiguous spikesedge, éléocharide ambiquë
often arching or recurved or reclining, their spikelets usually all fruiting simultaneously, long to very short in 1 tuft, subterete, 4–40 cm × 0.2–0.5 mm, soft.
terete, often with to 16 blunt ridges when dry, 25–80 cm × 0.5–1.5 mm, firm, internally spongy.
distal leaf sheaths persistent and evident or disintegrating (fugaceous) and not evident, proximally green or stramineous, brown, reddish, or purple, distally stramineous to green or colorless, papery to membranous, apex subacute to acuminate, sometimes with linear blade to 1 mm.
distal leaf sheaths persistent, not splitting, proximally dark red, distally red to stramineous or green, often callose, thinly papery (to membranous), apex dark red-brown, obtuse to subtruncate, tooth sometimes present on some culms, to 0.3 mm.
basal spikelets absent (often some spikelets subsessile); never proliferous, ovoid, terete, 2–10 × 1–2 mm, apex acute;
proximal scale empty or with a flower (usually in the same plant), deciduous or some persistent, amplexicaulous, similar to other scales (except apex sometimes rounded);
subproximal scale with a flower;
floral scales spiraled, 5–30, 5–6 per mm of rachilla, pale brown to colorless, often spotted brown, ovate, 1.5–2 × 1 mm, thinly membranous to translucent, midribs often green, evident to obscure, apex acute.
ovoid to lanceoloid, 5–23 × 2–3(–4) mm, apex acute (to obtuse);
proximal scale amplexicaulous, entire;
subproximal scale with flower;
floral scales often spreading in fruit, 10–60, 3–4 per mm of rachilla, medium brown, rarely red-brown, midrib regions mostly stramineous to green, in proximal part of spikelet ovate, in distal part lanceolate, 2.5–3.5 × 1.7 mm, entire, apex acute to rarely obtuse, often carinate in distal part of spikelet.
perianth bristles 6–7, pale brown to stramineous or whitish, slender, equaling to exceeding tubercles or rarely rudimentary to less than 1/2 achene length;
spinules sparse, retrorse, sharply acute;
stamens 3 (sometimes fewer?);
anthers 0.2–0.5 mm;
styles 3-fid.
perianth bristles 2–4(–5), brown, slender to stout, usually very unequal, rudimentary to equaling achene;
stamens 3;
anthers brown, 1.5–2 mm;
styles 2-fid, sometimes some 3-fid.
golden brown, narrowly obpyriform, proximally markedly narrowed, compressed-trigonous, angles slightly prominent, 0.9–1 × 0.6–0.75 mm, finely reticulate or pitted or papillose at 20–30X, apex usually constricted proximal to tubercle.
not persistent, dark yellow or stramineous, obovoid to obpyriform, all biconvex or some (very rarely all) compressedtrigonous, angles obscure, 1–1.5 × 0.9–1.25 mm, apex rounded, neck absent (to very short), finely rugulose at 10–20X, with 20 or more horizontal ridges in vertical series and/or finely cancellate at 10–30X.
brown, narrowly pyramidal to linear, trigonous, 0.3–0.4 × 0.1–0.25 mm.
brown or proximally whitish, pyramidal, depressed, rarely some as high as wide, 0.15–0.3(–0.5) × (0.3–)0.4–0.6 mm.
= 22.
= 44, 45, 46.
Eleocharis intermedia
Eleocharis ambigens
The flowers are mostly cleistogamous, with stigmas and stamens remaining enclosed in the floral scales except sometimes on the shortest culms. We have not seen specimens to confirm literature reports of E. intermedia from Iowa.
Eleocharis intermedia perhaps should be placed in sect. Intermediae (Svenson) Zinserling following I. Kukkonen (1990). H. K. Svenson (1929) placed it in his E. ser. Intermediae (name invalid) but later (1937, 1957) placed it in his E. subser. Truncatae (name invalid), and M. S. González-E. and P. M. Peterson (1997) placed it in E. subser. Truncatae. However, E. intermedia differs from all other members of ser. Eleocharis in its annual, tufted habit without evident, creeping rhizomes, culms varying in one tuft from long to very short, often with some spikelets subsessile, all spikelets of a tuft fruiting simultaneously, and the proximal scale often subtending a flower. It was placed in ser. Tenuissimae because of a resemblance to some other species of that series; closer observation reveals that it differs substantially in its achenes or habit from other members of ser. Tenuissimae. It rather closely resembles E. flavescens var. olivacea and E. geniculata in 8a2a. ser. Maculosae as well as small plants of species in 8a2b. ser. Ovatae.
Eleocharis macounii Fernald had been treated as a distinct species, or included within E. intermedia, E. obtusa, or E. ovata in the broad sense (including E. obtusa). P. M. Catling and S. G. Hay (1993) presented morphologic evidence suggesting that E. macounii Fernald is a hybrid between E. intermedia and E. obtusa, and named it E. ×macounii (Fernald) P. M. Catling & S. G. Hay. It is known only from the type collection from 1893 and a second collection from 1987, both from along the Gatineau River north of Ottawa in southwestern Quebec. Its habit is very similar to that of E. intermedia, from which it differs mainly in its achenes lenticular to trigonous in the same plant, the two or three angles prominent, keeled, costate, the surface smooth or very finely reticulate or pitted at 30X, and tubercles 0.2–0.5 mm wide. It produces few achenes, whereas E. intermedia and E. obtusa usually produce abundant achenes. In the protologue M. L. Fernald (1899) compared E. macounii with the Eurasian E. carniolica W. D. J. Koch. H. K. Svenson (1929, 1937) compared it with both E. intermedia and the Eurasian E. multicaulis (Smith) Smith and later (1957) placed it in synonymy under E. obtusa. Pending further research, it seems best to treat the two known collections of E. macounii as probable hybrids between E. intermedia and either E. obtusa or E. ovata; all three species are sympatric in the region where the collections of E. macounii were made (P. M. Catling and S. G. Hay 1993; B. M. H. Larson and P. M. Catling 1996).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Eleocharis ambigens is usually treated as a synonym of E. fallax because some specimens from Massachusetts to Georgia have some 3-fid styles and some obscurely trigonous achenes. A specimen of E. ambigens from Louisiana has trigonous achenes. Eleocharis ambigens is very similar to and perhaps better included in E. uniglumis (S.-O. Strandhede 1967). Intermediates with E. macrostachya occur in Louisiana and Texas. The depressed tubercles are diagnostic of E. ambigens. Eleocharis ambigens is sometimes confused with E. montevidensis, which is readily distinguished by its floral scales with broadly rounded apices.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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