Rhynchospora nivea Boeckeler
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Authority
Thomas, William W. 1984. The systematics of Rhynchospora section Dichromena. Mem. New York Bot. Gard. 37: 1-116.
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Family
Cyperaceae
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Scientific Name
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Description
Species Description - Cespitose, glabrous perennial (Fig. 2c); culms erect to occasionally arching, 736 cm tall, 0.2-0.8 mm in diameter, green, terete; leaves 3-6 per culm, cauline and basal linear to occasionally filiform, flat to occasionally involute, green; basal leaves 1-3 per culm, 3-15 cm long, 0.2-2.1 mm wide; uppermost cauline leaves 3-8 cm long 0.2-1.3 mm wide; uppermost leaf sheaths 0.3-2.1 mm long, green: summit of inner band truncate to slightly prolonged, hyaline; inflorescence bracts green slender somewhat reduced, 1-3 exceeding inflorescence; basal bract longest 0.7-6 cm long 0 2-1.8 mm wide, dilated and paler at base; inflorescence (Fig. 13a) a congested, obconic head of ca. 3-11 spikelets; spikelets ovoid, 3.5-8 mm long, 1-2.4 mm wide, consisting of ca. 8-15 scales; scales white, occasionally ferrugineously streaked basally, ovate, 2.2-3.9 mm long, 1.5-2.5 mm wide, cymbiform, ± not carinate; filaments 2.4-3.5 mm long; anthers 1.4-1.7 mm long; stigma and style 3.4-3.9 mm long; stigma branches 1.6-1.9 mm long; achene (Fig. 1 la) lenticular, bilaterally symmetrical, golden to black, very widely obovate, 0.7-0.9 mm long and wide; summit of achene very strongly arched; shoulders of achene at edge of style base confluent with achene margin; style base roughly triangular but with tip attenuate and base concave, 0.2-0.4 mm high, 0.5-0.9 mm broad, reddish brown to black; achene surface transversely rugose; epidermal cells of achene narrowly elliptical to linear. Flowering and Fruiting: Flowering and fruiting takes place from April to October but is heaviest from May to July with few mature fruits developed before mid-May. Distinguishing Features: This cespitose species can be distinguished by its lightly rugose achenes, low number of usually narrow bracts, and narrow, often involute, leaves.
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Discussion
Type. Texas, 1847, Lindheimer 718 (GH, lectotype; B, GH, M, MO-2, NY-2, isolectotypes). Dichromena nivea (Bõckeler) Britton, Bull. Torrey Bot. Club 15: 101. 1888. Dichromena diphylla Torrey in Bõckeler, Linnaea 37: 528. 1872, nom. nud. Dichromena reverchonii S. H. Wright, Bull. Torrey Bot. Club 9: 86. 1882. [as "reverchoni"]. Type: Texas, Dallas Co. near Turtle Creek, 1881, J. Reverchon 1233 (MO, lectotype; F, isolectotype). Pollination: Visitors to this species were quite frequent, bees (especially Lasi-oglossum) much more so than flies. In contrast to most species, anthers do not emerge and insects do not visit inflorescences until late morning. The following insect visitors were collected: Lasioglossum (Dialictus) spp., Megachile cf. brevis, and Sphaerophoria sp. Nomenclature: In determining the type of Dichromena reverchonii, label data are not reliable. It has been generally assumed that Rever chon 1233 is the type collection of this name; however, not all specimens with this number were collected in the proper year. Wright states that “a very few” specimens collected in 1881 from Turtle Creek were the ones from which the description was written. The collection number 1233 is on handwritten labels from Turtle Creek and also on printed labels from the “upper Seco.” Furthermore, the date for number 1233 is variously given as 1880 and 1881, perhaps including a larger number of nonfruiting specimens collected in 1880. It seems likely that only the few handwritten labels from the Reverchon herbarium, which have both the date and locality of the type description, fit Wright’s statement; these are certainly type specimens-the status of other specimens with contradictory information remains unclear.
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Distribution
Habitat: This species is found near the edges of streams and may be subject to inundation in the early spring. The plants grow on marl, in sand, or out of cracks or crevices in limestone rock. The soils at several localities in Oklahoma and Texas all had pH readings of approximately 8. This species often occurs in uniform stands or singly when growing in rocky areas. Associated plant species, when present, are those typical of open stream banks and wet areas.
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