Eleocharis elliptica (Elliptic Spikerush)

Plant Info
Also known as:
Genus:Eleocharis
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Habitat:sun; wet; fens, marshes, shores, sedge meadows, prairie swales
Fruiting season:July - September
Plant height:2 to 36 inches
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: indistinct Cluster type: spike

[photo of spikes] A single spike at the top of the stem, lance-elliptic in outline, blunt to pointed at the tip, 3 to 8 mm (to ~1/3 inch) long, with 10 to 30 florets spirally arranged, each floret subtended by a single scale. Scales are 1.7 to 3 mm long, mostly blunt at the tip, reddish-brown to dark brown to nearly black with a green to straw-colored midrib and a wide band of whitish translucent edging. The scale tip is often shallowly notched, especially in the upper spike, the whitish part not more than .6 mm long and not longer than wide. Florets have 3 stamens and usually a 3-parted style, sometimes 2-parted. The lowest scale in the spike is rounded and not notched at the tip, wraps 100% of the stem, and lacks a flower. The second lowest scale has a flower.

Leaves and stems: Leaf attachment: basal Leaf type: simple

[photo of sheaths] The 2 leaves are bladeless and reduced to sheaths on the lower stem. The upper sheath is membranous, dark reddish toward the base, green to yellowish to red towards the tip, may be darker reddish-brown around the tip edge, the front rounded to pointed at the tip, and may have an obscure to distinct tooth at the apex.

[photo of stem cross-sections] Stems are mostly round in cross-section, sometimes slightly compressed (less than 3 times as wide as thick), .3 to .8 mm wide, often with 5 to 10 vertical ridges or angles. Stems are erect and form mats from long rhizomes.

Fruit: Fruit type: seed without plume

[photo of scales and achenes] Each flower produces a single achene (seed), that persists on the spike after the scale drops off, the achene with a cap-like appendage (tubercle) at the tip that is clearly distinct from the rest of the achene. Scales become spreading in fruit. Achenes are .7 to 1.2 mm long, .6 to .9 mm wide, yellow to orange to brown, covered in a fine network pattern, 3-sided to nearly lens-shaped in cross-section, urn-shaped in outline, rounded at the tip end and tapering at the base. Tubercles are greenish to brown, pyramidal and usually depressed, .1 to .3 mm long, mostly wider than long. There is barely a neck/constriction between the tip of the achene and the base of the tubercle. Surrounding the achene are 0 to 3 (usually 0) barbed, whitish to light brown bristles, up to half as long as the achene.

Notes:

Eleocharis ellipitca is one of several colony-forming Spikerushes in Minnesota and can be difficult to distinguish from some of the others even when achenes are present. The achenes are virtually identical to those of Eleocharis compressa, and the two were at one time considered varieties of a single species and are still identified as such in some references. Both may be found in a variety of wet habitats, from road ditches to sedge meadows to seeps and seasonally wet depressions, often in calcareous soils.

E. elliptica is distinguished by stems that are mostly round in cross-section but with up to 10 ribs/angles, at least some floral scales with a notch at the tip, usually yellow-orange achenes about 1 mm long with a conspicuous network pattern across the surface, achenes persisting on the spike after scales drop off, up to 5 bristles (often absent) of varying lengths, tubercle depressed and usually wider than long. The spike is normally lance-elliptic, blunt at the tip, with brown scales and the second lowest scale may have a flower/fruit. Some references note 3 varieties of E. elliptica, but these are not recognized in Minnesota.

By comparison, E. compressa floral scales are typically deeply notched at the tip, the whitish edging on the scale tip longer than wide, stems are mostly compressed and often twisted, and most achenes do not persist on the spike after the scales drop off. The persistent achenes is a trait shared with Eleocharis nitida, which is a much more diminutive plant with thread-like stems, scales less than 1.5 mm long, achenes less than .7 mm long, and which is only found in the arrowhead region of MN.

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More photos

Photos by K. Chayka taken in Anoka, Cook and Lake counties. Photos courtesy Peter M. Dziuk taken in Lake County.

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