8c. ELEOCHARIS R. Brown subg. ZINSERLINGIA T. V. Egorova, Novosti Sist. Vyssh. Rast. 18: 101. 1981.
Eleocharis sect. Baeothryon (Gray) S. González & P. M. Peterson; Scirpus Linnaeus sect. Baeothyron Gray
Plants perennial, never with spikelets proliferating or culms rooting at tips. Rhizomes present, creeping. Bulbs (resting buds) often present, terminating short rhizomes or among culm bases. Culms 5–40 cm × 0.3–1.2(–2.5) mm, spongy, transverse septa incomplete. Spikelets ovoid or oblong, terete, usually much wider than their culms, 3–10 mm; rachilla with several proximal internodes shorter and thicker than internodes in middle of spikelet; proximal scale subtending a flower or empty; floral scales ca. 4–12 per spikelet, spiraled, 2.5–6 mm, with 1 vein, membranous. Styles 3-fid, or 3-fid and 2-fid. Achenes trigonous, or trigonous and biconvex, usually distally narrowed into a distinct beak, 1.5–2.7 mm, smooth or finely longitudinally ridged, the outer anticlinal epidermal cell walls often forming a fine whitish reticulum. Tubercles often merging with achene summit in form, texture, and color, not dorsoventrally greatly compressed.
Species ca. 8 (4 in the flora): temperate and boreal North America, South America (Argentina, Chile), Eurasia.
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.