Eleocharis engelmannii (Englemann's Spikerush)

Plant Info
Also known as: Engelmann's Spikesedge
Genus:Eleocharis
Family:Cyperaceae (Sedge)
Life cycle:annual
Origin:native
Habitat:sun; moist sandy or rocky soil; shores, mudflats, rock outcrops
Fruiting season:July - October
Plant height:2 to 16 inches
Wetland Indicator Status:GP: FACW MW: FACW NCNE: FACW
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 to cylindric in outline, mostly blunt at the tip, 5 to 15 mm (to .6 inch) long, with 25 to 200 florets (usually more than 40) tightly packed and spirally arranged, each floret subtended by a single scale. Scales are 1.7 to 2.5 mm long, 1 to 1.3 mm wide, rounded at the tip, orange-brown to straw-colored with a green midrib that dries brown. Florets have a 2- or 3-parted style (often mixed in the same spike) and usually 3 stamens. The lowest scale in the spike is smaller than the rest with a broad green central band, surrounds about 2/3 of the stem, and lacks a flower. The second lowest scale is like the lowest.

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 firm, concave on the back, the front blunt to pointed at the tip with a tooth at the apex that is up to .3 mm long. Sheath bases are green to straw-colored to brown to reddish. Stems are straight, ribbed, erect to ascending, usually of varying lengths, .5 to 2 mm diameter. Plants form dense clumps.

Fruit: Fruit type: seed without plume

[photo of scale and achenes] Each flower produces a single achene (seed), that drops off independently of the scale, the achene with a cap-like appendage (tubercle) at the tip that is clearly distinct from the rest of the achene. Achenes are .9 to 1.1 mm long, straw-colored to dark chestnut brown, smooth across the surface, shiny, lens-shaped in cross-section, urn-shaped in outline, rounded at the tip end and tapering at the base. Tubercles are brown, broadly and shortly triangular, more than 2/3 as wide as the achene, depressed and less than 1/3 as long as wide. There is no neck or constriction between the top of the achene and the base of the tubercle. Surrounding the achene are 5 to 8 (sometimes 0) barbed, brown bristles, usually much shorter than the achene.

Notes:

Eleocharis engelmannii is one of several clump-forming Spikerushes in Minnesota and can be difficult to distinguish from some of the others when achenes are absent. It is most similar to Eleocharis obtusa and Eleocharis ovata, and the three were at one time all considered a single species and are still identified as such in some references. All three may be found in a variety of wet habitats, from road ditches to wet meadows to receding shores to seasonal pools in rock outcrops, though collection records in Minnesota indicate E. engelmannii is more often found in outcrops than the other two. E. engelmannii is distinguished by the shiny and smooth lens-shaped achene, bristles usually much shorter than the achene, and tubercle that is 2/3 or more as wide as the achene, depressed and less than 1/3 as tall as wide. The spike is normally cylindric to lance-elliptic, blunt at the tip, with orange-brown scales.

Like E. englemannii, the tubercle on E. obtusa achenes is at least 2/3 as wide as the achene, but is not depressed so appears proportionately much taller, and its bristles are typically longer than the achene. E. ovata has bristles like those of E. obtusa, but its tubercle is less than 2/3 as wide as the achene and more narrowly triangular, often as tall as wide, and its floral scales are usually purple-brown rather than orange-brown.

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More photos

Photos courtesy Peter M. Dziuk taken in Brown, Renville and Rock counties.

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