Flora of North America species comparison

Eleocharis acicularis is abundant and ecologically important throughout much of its range. It occurs in a wide variety of habitats, including acid waters. I have not seen voucher specimens for reports from Alabama and Florida. I have not seen vouchers for the reported chromosome numbers of 2n = 30–38 or 50–58.

Eleocharis acicularis often forms large rooted mats or floating masses, which when submerged, are often non-flowering. Submerged, usually nonflowering plants are abundant throughout much of the range of the species (H. K. Svenson 1929; P. E. Rothrock and R. H. Wagner 1975). They have been called E. acicularis forma fluitans (Doellinger) Svenson; E. acicularis forma inundata Svenson; E. acicularis forma longicaulis (Desmazières) Hegi; E. acicularis forma submersa (Nilsson) Norman; and E. acicularis var. submersa (Nilsson) Svenson. The culms of the submerged plants are terete, smooth, soft to flaccid, translucent, and the partitions of the air cavities within are clearly visible. Submerged plants may closely resemble aquatic forms of some other species, especially Eleocharis parvula, E. robbinsii, and Schoenoplectus subterminalis (Torrey) Sojak (N. C. Fassett 1957; E. G. Voss 1967, 1972–1996, vol. 3).

Although E. acicularis is very variable, recognition of varieties is premature pending a worldwide taxonomic revision of subg. Scirpidium. Much of the variation is apparently due to phenotypic plasticity in response to environmental factors, especially water depth (P. E. Rothrock and R. H. Wagner 1975). The named varieties intergrade extensively, and achenes, which are important in defining the varieties, are often absent. H. K. Svenson (1929) recognized four varieties and two forms for North America, but later (1957) did not recognize infraspecific taxa.

Most plants from the Arctic to cool-temperate North America, including higher elevations in the Southwest, are very similar to plants from northern Europe and presumably belong to typical E. acicularis, which was described from Europe. Those plants have culms cylindric or three- to four-angled; leaf sheaths mostly obscure and closely sheathing; and achenes about two times longer than wide.

Eleocharis acicularis var. gracilescens Svenson, type from St. Louis, Missouri, applies to plants with flowering culms unusually long (to 60 cm), smooth or sometimes with five to twelve fine ridges, their bases not cormlike; spikelets often linear-lanceoloid, often unusually long (to 8 mm); floral scales often unusually long (to 3.5 mm), often stramineous; and achenes much less than two times longer than wide. Plants of E. acicularis var. gracilescens are probably usually emergent in shallow water; they are known from scattered collections from Alabama, Florida, Kansas, Missouri, North Dakota, Oklahoma, South Carolina, Tennessee, and Texas. Robust plants of E. acicularis var. gracilescens are sometimes misidentified as E. wolfii. H. K. Svenson (1957) stated that var. gracilescens may be distinct from E. acicularis. Some specimens from California and Oregon that resemble E. acicularis var. gracilescens may be ecologic forms of E. acicularis var. occidentalis.

Eleocharis acicularis var. occidentalis Svenson, type from Santa Barbara, California (illustrated in H. L. Mason 1957; H. K. Svenson 1939, plate 539), applies to plants with culms only 2–6 cm, smooth or usually some prominently four-angled or finely to ca. eight-ridged, their bases often persistent, swollen, and cormlike (illustrated herein); distal leaf sheath summits mostly evident, often markedly inflated; achenes much less than two times longer than wide. This variety often grows in vernal pools. As here defined, it is known only from Arizona, California, and Nevada. Most of the specimens H. K. Svenson (1929) cited in the protologue and identified on herbarium specimens as E. acicularis var. occidentalis are probably referable to typical E. acicularis.

Eleocharis acicularis var. porcata S. G. Smith (S. G. Smith 2001), type from Texas, applies to plants that are similar to E. acicularis var. occidentalis except that their culms (cross section illustrated herein) reach 22 cm × 0.5 mm, some or all are prominently six- to twelve-ridged and mostly distinctly compressed, and their bases are not cormlike. This variety grows in mud and shallow water of marshes, ponds, and stream margins; it is known from Alberta, Arizona, Colorado, Illinois, Kansas, Louisiana, Nebraska, New Mexico, North Dakota, and Texas. Because of their compressed, prominently-ridged culms, robust plants of E. acicularis var. porcata, including a paratype of E. wolfii, are sometimes misidentified as E. wolfii (S. G. Smith 2001).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Eleocharis palustris is the most widespread and common species of the extremely difficult circumboreal “E. palustris complex,” which in North America comprises E. palustris, E. mamillata, E. macrostachya, E. erythropoda, E. uniglumis, E. kamtschatica, and E. ambigens. Two or more of these species have been combined by recent authors. The complex has been studied extensively only in northern Europe (S.-O. Strandhede 1965, 1966), where E. palustris, E. mamillata, and E. uniglumis are recognized (S.-O. Strandhede 1966). European studies and preliminary studies in North America by S.-O. Strandhede (1967) and L. J. Harms (1968) indicate that unstable chromosome structure and number as well as interspecific hybridization contribute to the taxonomic complexity of the E. palustris complex.

Eleocharis palustris is extremely variable worldwide. Recognition of infraspecific taxa outside northwestern Europe is premature. For northern Europe, S.-O. Strandhede (1966) recognized E. palustris subsp. palustris, with two varieties, for which the chromosome numbers 2n = (14–)16(–17) have been reported, and E. palustris subsp. vulgaris, without varieties, for which the chromosome numbers 2n = (33–)38–39(–40) have been reported. Eleocharis palustris subsp. vulgaris is morphologically intermediate between E. palustris and E. uniglumis and may be of hybrid origin. Its North American counterpart appears to be the polyploid populations of E. macrostachya (variants b and c, at least in part), as defined herein. For North America, S.-O. Strandhede (1967) and L. J. Harms (1968) recognized two “cytotypes” among the plants with the morphology of E. smallii, one with 2n = 16 (variant a below) and one with 2n = 36 (variant c below). Much of the variation in habit is undoubtedly because of modification of the phenotype by environmental conditions as described for Europe by S.-O. Strandhede (1966). The more robust plants are often emergent in open water and may be called “crassa” phenotypes; the more slender plants often grow in densely vegetated marshes and meadows and may be called “meadow” or “grassland” phenotypes. Intermediates between E. palustris variant b (below) and E. erythropoda are common in zones of sympatry.

At least 4 variants are notable in North America.

Variant a (Eleocharis smallii in the strict sense) has culms mostly 1–3 mm wide; distal leaf sheaths sometimes disintegrating, often splitting adaxially, summits often with red margins, apices obtuse to broadly acute; floral scales 3–4 mm; achenes to 1.5(–1.6) mm; culm stomates 39–48 µm (based on very few measurements). Reported chromosome numbers for which I have seen vouchers, all from Kansas, are 2n = 16, 17 (L. J. Harms 1968). The range of variant a is mostly northeastern, where it is known from elevations to 1700 m in Newfoundland, west to Manitoba and south to North Carolina, Kentucky, Missouri, and Kansas, with one collection from east-central Alaska.

Variant b is similar to variant a and intergrades with it. It has culms only 0.5–1.2 mm wide; distal leaf sheaths persistent and not splitting, summits usually with markedly red margins, markedly oblique when viewed from the side, apices acute to narrowly obtuse; and spikelets with proximal scale often clasping 3/4 of the culm. At least some of these slender plants may simply be meadow or grassland forms produced by the direct effects of unfavorable enviromental factors such as competition. Variant b is mostly sympatric with variant a; it is more common in the Southeast, where it is known south to Louisiana and Arkansas. Plants from the more southern part of the range are especially striking because of their extremely oblique, brightly red-margined sheath summits and proximal floral scales usually clasping to 3/4 of the culm.

Variant c may be called Eleocharis palustris var. vigens L. H. Bailey. The lectotype is from the shores of Lake Champlain in Vermont (S. G. Smith 2001). It is similar to unusually robust forms of variant a, from which it differs in that its achenes are 1.6–2 mm, culm stomates 52–65 µm, and floral scales mostly 3.5–4.5 mm. Because of its large achenes and stomates, variant c is assumed to be tetraploid with 2n = 36 (S.-O. Strandhede 1967; L. J. Harms 1968). Variant c apparently grows mostly as an emergent in open water to about 1 m deep. Its known range is northeastern, from Newfoundland and Labrador to Manitoba, south to New York, Michigan, Wisconsin, and Nebraska.

Variant d comprises most of the plants that cannot be placed in the preceding variants. Most of these plants closely resemble most specimens that I have seen from northern Eurasia and as described for Eleocharis palustris subsp. palustris by S.-O. Strandhede (1966). Variant d has distal leaf sheaths often splitting or disintegrating, the summit margins not reddish, and apices usually broadly obtuse. In North America variant d is mostly subarctic and boreal; it is known from Newfoundland and Labrador to Alaska, south to New York, Wisconsin, Minnesota, Iowa, New Mexico, and California. Some plants of variant d that have markedly narrow tubercles mostly much (to 2 times) higher than wide and narrow achenes only 0.9–1.1 mm wide may deserve taxonomic recognition; they are known from Manitoba west to British Columbia and Alaska, south to Colorado, Utah, and California. Specimens of variant d from scattered western localities from Alaska and Yukon south to California have floral scales 4–5 mm and achenes 1.6–1.9 mm and are very similar to variant c.

(Discussion copyrighted by Flora of North America; reprinted with permission.)