Flora of North America species comparison

Plants treated as Eleocharis uniglumis fall within the large morphologic variation of Eurasian E. uniglumis. Two subspecies and 3 varieties were recognized for northern Europe (S.-O. Strandhede 1966), and five species that were recognized by I. D. Zinserling (1935) were placed in synonymy under E. uniglumis (S.-O. Strandhede 1966). Recognition of infraspecific taxa within North American E. uniglumis is premature. Plants commonly called E. halophila or E. uniglumis var. halophila, found mostly in Atlantic Coastal brackish habitats, have floral scales that are usually narrower and more densely placed on the rachilla than plants usually called E. uniglumis, which are found mostly in the interior; some plants are intermediate in expression of these characters. The achene and tubercle shape characters used by M. L. Fernald (1950) to distinguish E. uniglumis from E. halophila are not valid. In North America, E. uniglumis is difficult to separate from E. erythropoda and E. kamtschatica, in both of which the spikelets have only the proximal scale without a flower (empty) and the proximal scale completely amplexicaulous. Eleocharis uniglumis differs from E. erythropoda only in its broader floral scales, which are less densely placed on the rachilla; it differs from E. kamtschatica only in its smaller tubercles. It is also difficult to separate from some specimens of E. macrostachya in which the spikelets have proximal scales that are sometimes completely amplexicaulous; such plants differ from E. uniglumis only in the absence of a flower in the axil of the subproximal scale of some of the spikelets. I have not seen voucher specimens for the chromosome numbers of 2n = 27 and 28 reported by S.-O. Strandhede (1967) from Massachusetts and Nebraska, which are lower than the 2n = (44–)46(47–88) reported for Europe (S.-O. Strandhede 1965).

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

The chromosome numbers 2n = 10 and 2n = 16 have also been reported from North America but have not been verified.

Eleocharis macrostachya probably occurs in Saskatchewan; I have not seen specimens. It is extremely variable. Cytotaxonomic studies (S.-O. Strandhede 1967; L. J. Harms 1968) and morphology suggest that it is a diploid-polyploid complex at least partly of hybrid origin from E. palustris and both E. erythropoda and E. uniglumis. The 2n = 38 plants of E. macrostachya may comprise the American counterpart of the European E. palustris subsp. vulgaris, which presumably originated from E. palustris subsp. palustris and E. uniglumis (S.-O. Strandhede 1966). Although recognition of infraspecific taxa is premature, the following three intergrading variants are notable:

Variant a (= Eleocharis xyridiformis) almost certainly deserves taxonomic recognition, perhaps as a species. It has markedly compressed culms to 3 times wider than thick; distal leaf-sheath apices subtruncate, usually with a tooth to 0.6(–1) mm on some or all culms; spikelets narrowly lanceoloid; floral scales medium brown to stramineous, mostly lanceolate and carinate, 2.5–4 × 1.5 mm; achenes 1.1–1.5 × 0.8–1.2 mm; chromosome numbers (for which I have seen vouchers, all from Kansas and South Dakota), 2n = 18. It is known from 20–450 m in Arizona, California, Illinois, Kansas, Missouri, New Mexico, Oklahoma, South Dakota, Texas, and Mexico (Coahuila, Durango, Nuevo León). Both the holotype of E. xyridiformis from Mexico and the vouchers of the 2n = 18 chromosome counts reported for E. xyridiformis, all from Kansas and South Dakota, have stomates 55–60 µm, which is typical of 2n = 18 plants (S.-O. Strandhede 1967). The holotype of E. macrostachya from Oklahoma, which is otherwise much like the type of E. xyridiformis except for less markedly compressed culms, has stomates averaging 59–68 µm, which is typical of plants of E. macrostachya with 2n = 38 as in variant b.

Variant b is very variable in comparison with variant a. It differs from variant a in having culms terete or slightly compressed; distal leaf-sheath apices often obtuse, tooth rarely present, to 0.1 mm; spikelets broadly lanceoloid to ovoid; floral scales 3.5–4(–4.5) × 1.7–2+ mm; achenes 1.3–1.5 mm, rarely to 1.8 mm; culm stomates 60–72 µm; chromosome numbers (for which I have seen vouchers, all from Kansas and South Dakota), 2n = ca. 38. It is wide-ranging, known from inland localities at 20–2300 m from Manitoba west to Yukon and British Columbia, south to Alabama, Mississippi, Louisiana, Texas, New Mexico, Arizona, and California, and in Mexico from Baja California. Intermediates between variant b and both Eleocharis erythropoda and E. uniglumis are widespread, and intermediates with E. ambigens occur in Louisiana. Most plants of variant b have floral scales to 4 mm and achenes to 1.5 mm; plants with scales to 4–5 mm and achenes sometimes more than 1.6 mm occur in California, Nevada, Oregon, and Washington.

Variant c differs from variant b in having spikelet scales mostly uniformly dark chestnut-brown, not carinate, (3.5–)4–5.5 × 2–2.5 mm. Its achenes are often unusually large, 1.3–1.8(–2) × 1.1–1.5 mm. It is known from near sea level on the coasts of British Columbia, Ontario, and Quebec (James Bay and Magdalen Islands); Alaska, California, Oregon, and Washington. Some plants are intermediate between variant c and variant b. Several specimens I have seen from far eastern Russia are very similar to American plants of Eleocharis macrostachya, variant c. Except for having incompletely amplexicaulous proximal scales, and subproximal scales often without a flower, variant c closely resembles many Eurasian specimens of E. uniglumis.

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