Eleocharis robbinsii |
Eleocharis minima |
|
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Robbin's sppike-rush, Robbins' spikerush, Robbins' spikesedge, éléocharide Robbins |
small spikerush |
|
Habit | Plants perennial; rhizomes (0.5–)1–2 mm thick, longer internodes 2–3 cm, scales 5–7 mm; tubers sometimes present, apical, ovoid, 4–8 × 3–4 mm. | Plants annual, tufted, often mat-forming, often stoloniferous, sometimes entirely vegetative; rhizomes absent. |
Culms | acutely trigonous; spikelet-bearing culms 16–70 cm × 0.7–0.9 mm; when submersed plants often forming numerous, filiform, flaccid culms without spikelets, sometimes with whorls of slender branches, 0.1–0.3 mm wide; soft, sometimes septate-nodulose when aquatic, internally spongy, transverse septa incomplete. |
erect, ascending or arching, quadrangular, sulcate, 1–13 cm × 0.1–0.3 mm, soft. |
Leaves | distal leaf sheaths persistent or decaying, membranous, apex obtuse to acuminate. |
distal leaf sheaths persistent or disintegrating, red-brown, stramineous, green, or mottled red-brown, translucent, apex narrowly acute. |
Spikelets | sometimes proliferous (when submerged), 9–33 × 1.5–3 mm; rachilla joints bearing prominent winglike remnants of floral scales; proximal scale with a flower, amplexicaulous, (5–)6–9.8 mm; floral scales 4–18, 0.5–1 per mm of rachilla, stramineous to pale brown, often minutely dotted reddish, without or rarely with darker submarginal band, narrowly ovate to lanceolate, 5–7.8 × 2–3 mm, thickly papery, membranous toward margins, apex narrowly rounded to acute. |
basal spikelets often present, bisexual; often proliferous, ovoid or ellipsoid, laterally compressed when young, but terete at maturity, 2–7 × 1–2.6 mm, acute; proximal scale empty, often persistent, amplexicaulous, similar to floral scales; subproximal scale with a flower; floral scales spirodistichous (superficially appearing ± spiraled), (4–)10–28, 6–9 per mm of rachilla, pale brown, mottled red-brown to purple, ovate or elliptic, 1.3–2.1 × 0.7–1 mm, membranous, midribs green and red-brown, prominent, apex rounded to obtuse. |
Flowers | perianth bristles 6–7, stramineous to reddish brown, proximally slightly flattened, subequal to equal, much exceeding to rarely shorter than achene, 3–5 mm, retrorsely spinulose; anthers yellow to reddish, 1.6–3.2 mm; styles 3-fid. |
perianth bristles 6, colorless, white, or stramineous, slightly shorter than to equaling achene, spinules retrorse, acute; stamens 3; anthers 0.4–0.5 mm; styles 3-fid. |
Achenes | stramineous or medium brown, biconvex or compressed trigonous, narrowly obpyriform, 1.9–2.6 × 1–1.4 mm, adaxial face with 15–22 rows of rectangular, transversely elongated or nearly isodiametric cells, clearly sculptured at 10–15X, apex usually conspicuously constricted to short neck 0.4–0.7 mm wide, usually wider at tubercle base. |
greenish or pale brown or red-brown, often clearly spotted greenish or red-brown, ellipsoid to obovoid, trigonous (or terete?), angles prominent (keeled), 0.6–0.8 × 0.4–0.5 mm, apex constricted proximal to tubercle, smooth. |
Tubercles | stramineous to medium brown, high-pyramidal, 0.5–1.1 × 0.3–0.7 mm. |
red-brown, pyramidal, trigonous, 0.1–0.3 × 0.2–0.4 mm. |
Eleocharis robbinsii |
Eleocharis minima |
|
Phenology | Fruiting late spring–late fall. | Fruiting mid spring–fall. |
Habitat | Shallow waters of fresh lakes and ponds with sandy-peaty soils | Freshwater, sandy and peaty shores of lakes, muddy areas |
Elevation | 10–500 m (0–1600 ft) | 0–400 m (0–1300 ft) |
Distribution |
AL; CT; DE; FL; GA; MA; ME; MI; MN; NC; NH; NJ; OH; SC; VA; WI; NB; NS; ON; QC
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FL; MD; TX; Mexico; South America; West Indies; Central America (Costa Rica, El Salvador, Guatemala, Nicaragua, Panama) |
Discussion | I have not seen voucher specimens for literature reports of Eleocharis robbinsii from Indiana, Pennsylvania, or Rhode Island. Plants from South Carolina with the achene surface cells nearly isodiametric, the achene apex spongy, and the anthers to 3.2 mm may represent an undescribed taxon. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Eleocharis minima is most often confused with E. bicolor and E. baldwinii (see comments under 33. E. bicolor). Although floral scales in E. minima often superficially appear to be spirally disposed, in reality they are spirodistichous, ± decussate, while in E. baldwinii they are strictly distichous in one plane. The number of floral scales per millimeter is much greater in E. minima than in E. baldwinii. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 23, p. 117. | FNA vol. 23, p. 97. |
Parent taxa | Cyperaceae > Eleocharis > subg. Limnochloa | Cyperaceae > Eleocharis > subg. Eleocharis > sect. Eleocharis > ser. Tenuissimae |
Sibling taxa | ||
Synonyms | Chaetocyperus jamesonii, Chaetocyperus polymorphus, Chaetocyperus viviparus, E. durandii, E. jamesonii, E. minima var. ambigua, E. oropuchensis, E. savannarum, E. subtilis, E. tenuissima, E. villaricensis, E. wrightiana, Isolepis ambigua | |
Name authority | Oakes: Mag. Hort. Bot. 7: 178. (1841) | Kunth: Enum. Pl. 2: 139. (1837) |
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