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Aquatic and Wetland Vascular Plants of the Northern Great Plains

Eleocharis R. Br. -- Spikesedge, spikerush


Short to intermediate rushlike plants, mostly perennial from rhizomes (tufted and annual in E. obtusa), often forming extensive, dense, matlike colonies; culms slender and scapose, terete or compressed, sometimes angled and grooved. Leaves bladeless, reduced to sheathing at the base of the culm, the sheaths truncate to oblique at the summit. Inflorescence consisting of a single spikelet terminating the culm, the spikelet often subtended by 1-2(3) sterile scales (reduced bracts); scales of the spikelets spirally arranged and imbricate. Flowers perfect; perianth of usually 6 bristles, but often fewer or more, or the perianth lacking; stamens 3; styles bifid or trifid, the style base swollen and persistent as a tubercle atop the achene (or sometimes confluent with and not always clearly distinct from the achene body). Achenes biconvex or trigonous, crowned or beaked by the persistent tubercle.

The predominant spikerushes of regional marshes, meadows, shores and ditches are plants of the Eleocharis palustris (L.)R. & S. complex. Although many authors assign these plants to E. palustris, I have chosen to follow Harms (1968) in recognizing E. macrostachya, E. erythropoda, E. smallii and E. xyridiformis as distinct from the principally Eurasian E. palustris. Morphological distinction of these species is sometimes problematic, but cytological evidence lends support to their integrity as species. More study of the E. palustris complex is needed on a worldwide basis.

References:
  
Harms, L. J.  1968.  Cytotaxonomic studies in Eleocharis subser. 
     Palustres:  central United States taxa.  Amer. J. Bot. 55:966-974. 

Svenson, H. K.  1957. Eleocharis.  North Amer. Flora 18:509-540.

Lead Characteristic Go To
1 Achenes biconvex; styles bifid (often trifid or both trifid and bifid in E. obtusa). Lead 2
1 Achenes trigonous to nearly terete; styles trifid. Lead 6
2 Tubercles flat, triangular, sharp-edged, tightly fitting to the top of the achene; plants annual, producing fibrous roots only. E. obtusa
2 Tubercles thick, deltoid to conic, not sharp on the angles, constricted at the base where attached to the achene; plants perennial, rhizomatous. Lead 3
3 Sterile basal scales of the spikelet 2(3), each one not fully encircling the culm. Lead 4
3 Sterile basal scale 1, fully encircling the culm. E. erythropoda
4 Culms flattened, ribbonlike; tubercles deltoid, abruptly contracted into an attenuate apex. E. xyridiformis
4 Culms terete or subterete; tubercles conic, often mammillate. Lead 5
5 Basal sheaths sharply oblique at the orifice, with a prominent V-shaped sinus; culms often soft and inflated. E. smallii
5 Basal sheaths truncate to oblique; culms rigid. E. macrostachya
6 Tubercle not obviously differentiated from the achene, nor forming a distinct apical cap. Lead 7
6 Tubercle obviously differentiated from the achene, forming a distinct apical cap. Lead 9
7 Culms wiry, flattened above, mostly 4-10 dm long, 1-1.4 mm wide, some occasionally arching and rooting at the tip, tufted from a stout erect rootstock, lacking creeping rhizomes; spikelets 6-20 mm long, with 10-20 or more flowers. E. rostellata
7 Culms soft, terete, to 3 dm long, less than 1 mm thick, never rooting at the tip, arising in tufts from slender or filiform, creeping rhizomes; spikelets 2-8 mm long, 2- to 9-flowered. Lead 8
8 Lowest scale of the spikelet empty; scales mostly 1.5-2(2.5) mm long; achenes 0.9-1.3 mm long. E. parvula
8 Lowest scale of the spikelet subtending a flower; scales mostly 2.5-5.5 mm long; achenes 0.9-2.8 mm long. E. pauciflora
9 Achenes twice as long as wide, nearly terete, gray, with several longitudinal ridges and many fine crosslines. Lead 10
9 Achenes 2/3 to fully as wide as long, trigonous, golden to brown, distinctly roughened or pitted. E. compressa
10 Scales ca. 3 mm long; culms flattened, mostly 0.7-1.5 mm wide. E. wolfii
10 Scales ca. 2 mm long; culms scarcely flattened, 0.1-0.5 mm wide. E. acicularis


62. Cyperaceae, the Sedge Family
5. Elocharis R. Br. -- Spikesedge, spikerush
1. Eleocharis acicularis (L.) R. & S. -- Needle spikesedge
2. Eleocharis compressa Sulliv. -- Flatstem spikesedge
3. Eleocharis erythropoda Steud. -- Spikerush
4. Eleocharis macrostachya Britt. -- Spikerush
5. Eleocharis obtusa (Willd.) Schult. -- Blunt spikesedge
6. Eleocharis parvula (R. & S.) Link ex Buff. & Fingerh. -- Dwarf spikesedge
7. Eleocharis pauciflora (Lightf.) Link -- Few-flowered spikesedge
8. Eleocharis rostellata (Torr.) Torr.
9. Eleocharis smallii Britt. -- Spikerush
10. Eleocharis wolfii A. Gray -- Wolf's spikesedge
11. Eleocharis xyridiformis Fern. & Brackett -- Spikerush


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