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.)

Genera ca. 100, species ca. 5000 (27 genera, 843 species in the flora).

No consensus exists regarding the number of genera and the overall relationships of genera within Cyperaceae. The most recent account of the family (P. Goetghebeur 1998) recognized 104 genera distributed among 4 subfamilies and 14 tribes. That arrangement differs somewhat from that of J. Bruhl (1995). With one minor exception the arrangement of the family here follows that of Goetghebeur.

The family is characterized by the occurrence of a number of unusual cytological features including: (1) chromosomes with diffuse centromeres, (2) post-reductional meiosis, and (3) pollen grains formed from tetrads in which 3 of the 4 microspores fail to develop. The first two features are found in at least some Juncaceae and are unique to the two families. Juncaceae also have pollen in tetrads, but in that family all four microspores produce pollen grains. Some species in some genera of Cyperaceae (particularly Eleocharis) possess chromosomes with localized centromeres (S. S. Bir et al. 1993). The wide range of chromosome numbers found in Cyperaceae is largely because of agmatoploidy; polyploidy has been hypothesized for some genera, especially Eleocharis, although polyploidy has not been demonstrated unequivocally.

Because of morphologic similarities in vegetative and inflorescence characters, the family has commonly been associated with Poaceae. Cytological features discussed above clearly indicate that to be a superficial similarity. Data from rbcL studies also support the view that Cyperaceae and Poaceae are not closely related (M. R. Duvall et al. 1993b; G. M. Plunkett et al. 1995); they do support the concept of close relationship between Cyperaceae and Juncaceae.

For most families of flowering plants the phenological data given are flowering times. Because most Cyperaceae cannot be reliably identified when in flower, in this volume fruiting time is given for all species by season, sometimes qualified by early, mid, or late, or by months. The fruiting time has been interpreted broadly to include the period when the fruit is more or less fully formed but not yet ripe. The fruiting period provided covers the entire range of the taxon. Quite a difference between fruiting periods in different parts of the range of the species may well occur, especially for widespread species and species with extensive elevation range.

For a recent, comprehensive review of the economic importance of Cyperaceae, see D. A. Simpson and C. A. Inglis (2001).

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