Flora of North America species comparison

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.)

Species ca. 8 (4 in the flora).

The species of Eleocharis subg. Zinserlingia appear to be restricted to specialized, mostly groundwater-fed, often calcareous fens and other habitats. The achene beak is often interpreted as the tubercle because the tubercle often merges with and is difficult to distinguish from the achene apex. On the basis of similar form and color of the achene apex and tubercle, H. K. Svenson (1957) grouped in ser. Pauciflorae (Beauverd) Svenson all of the species that are here segregated into 8c. Eleocharis subg. Zinserlingia, 8a1a. E. ser. Rostellatae, and 8a3. E. sect. Parvulae, following M. S. González-E. and P. M. Peterson (1997).

All North American plants of Eleocharis subg. Zinserlingia were placed in E. pauciflora (Lightfoot) Link by H. K. Svenson (1957). Pending a much-needed worldwide revision, the treatment herein is based on the partial revision for North America by S. G. Smith (2001).

Vegetative reproduction in species of Eleocharis subg. Zinserlingia should be studied. The rhizomes are rather short and weak, and they are not evident on most specimens. The structures herein called bulbs are present on only about ten percent of North American and European herbarium specimens I have seen; bulbs are present on most collections from some populations in the Southwest. The bulbs were called “resting buds” by S.-O. Strandhede and R. M. T. Dahlgren (1968), who described and illustrated them for E. quinqueflora in Scandinavia. Bulbs or resting buds are not mentioned in major Eurasian floras (S. M. Walters 1980; I. D. Zinserling 1935), and it is not clear that they are produced by all Eurasian populations that are currently treated as E. quinqueflora. Bulbs vary greatly in size and shape, and they are tunicated with papery scales. Because the bases of some culm tufts of specimens of E. quinqueflora are slightly to greatly swollen (bulbous) and are tunicated by papery, two-veined, fibrous scales (prophylls) like those on the bulbs (but often longer), it seems likely that these bulbous-based culm tufts have developed from bulbs. With the exception of some high-elevation populations of E. quinqueflora in California, specimens with bulbs or bulbous culm-tuft bases do not have the well developed, hard caudices that are characteristic of the North American E. suksdorfiana, E. bernardina, and E. torticulmis, in all of which the terminal buds of the rhizomes are enlarged and are not known to form resting bulbs. Although bulbs are present on only a small percentage of herbarium specimens, most specimens of E. quinqueflora in North America can be identified using the presence of bulbous culm-tuft bases, the absence of well-developed, hard caudices, and/or spikelets with a flower in the axil of the proximal scale.

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