Eleocharis erythropoda (Bald Spikerush)
|Also known as:||Red-footed Spike-sedge|
|Habitat:||sun; wet; ditches, swales, shores, marshes, wet meadows, fens, disturbed soils|
|Fruiting season:||July - September|
|Plant height:||3 to 30 inches|
|Wetland Indicator Status:||GP: OBL MW: OBL NCNE: OBL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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A single spike at the top of the stem, lance-elliptic in outline, usually pointed at the tip, 3 to 18 mm (to ~¾ inch) long, with 15 to 50 florets spirally arranged, each floret subtended by a single scale. Scales are 2 to 3.5 mm long, blunt to pointed at the tip, reddish or orange-brown to medium brown with a green to straw-colored midrib and translucent edging. Florets have 3 stamens and a 2-parted style.
The lowest scale in the spike is similar to the rest, though more rounded at the tip, completely wraps around the stem at the base, and lacks a flower. The second lowest scale is similar to the lowest and does have a flower.
Leaves and stems:
The 2 leaves are bladeless and reduced to sheaths on the lower stem. The upper sheath is firm and persistent, usually reddish towards the base, green to yellowish towards the tip, often darker reddish-brown and slightly thickened all around the tip edge, straight across to concave on the back, the front rounded to blunt at the tip, sometimes with an obscure tooth at the apex. Stems are erect, .3 to 1.4 mm (usually .7 or less) diameter, round in cross section, with 8 to 12 vertical ribs that become conspicuous when stems dry. Plants form colonies from slender rhizomes.
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 1.6 mm long, .7 to 1.2 mm wide, yellowish to dark brown, smooth or with a very fine wrinkled texture on the surface, lens-shaped in cross-section, urn-shaped in outline, rounded at the tip end and tapered near the base. Tubercles are whitish to dark brown, pyramidal, .3 to .7 mm long, usually about as high as wide but may be much higher. A short neck/constriction exists between the tip of the achene and the base of the tubercle. Usually surrounding the achene are 4 barbed bristles, pale brown to whitish, about as long as to slightly longer than the achene. Bristles are sometimes absent.
Eleocharis erythropoda is one of several common, colony-forming Spikerushes in Minnesota and can be difficult to distinguish from some of the others, even when achenes are present. It is most similar to Eleocharis palustris and Eleocharis macrostachya, and all three were at one time considered a single species and are still identified as such in some references (including the national distribution map above). All three may be found in a variety of wet habitats, from road ditches to wet meadows to lake shores, in fresh to brackish waters. All three are also rather variable species, which confounds the situation.
E. erythropoda is distinguished by: stems round in cross-section and mostly less than 1mm diameter, sheaths rounded to blunt at the tip on the front (only sometimes with an obscure tooth at the apex), the lowest scale on the spike wraps completely around the stem, the second lowest scale has a flower/fruit, achenes are smooth, brown and lens-shaped in cross-section, usually with 4 bristles about as long as to slightly longer than the achene, and a whitish to dark brown cone-shaped tubercle usually about as tall as wide, though may be much taller. The spike is normally lance-elliptic, pointed at the tip with red-brown, orange-brown or medium brown scales to 2 to 3.5 mm long with blunt to pointed tips. Magnification may be required to see some of these traits.
By comparison, on E. palustris the lowest scale wraps less than 75% of the stem, the next lowest 1 or 2 scales lack flowers/fruit, floral scales are typically larger (3 to 5 mm long), and robust plants have stems up to 4 mm diameter. On E. macrostachya, stems are often compressed (up to 3 times as wide as thick), sheaths are more likely have a tooth at the apex, the lowest scale wraps about 70% or more of the stem, the second lowest scale may or may not have a flower/fruit, and the bristles are sometimes much shorter than the achene. To reiterate: these are all variable species so your mileage may vary. A fourth species, Eleocharis mamillata, also resembles this group but usually has 5 or 6 bristles that are distinctly longer than the achene, and has only been recorded 3 times in Minnesota, all in the arrowhead region near the Canadian border.
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- Eleocharis erythropoda plants
- Eleocharis erythropoda in a wet park lawn
- Eleocharis erythropoda in shallow water
- Eleocharis erythropoda at a construction site
- dense colonies in a marsh
- flowering spikes
- comparison of E. erythropoda, E. macrostachya and E. palustris lower scales
- comparison of Minnesota's Eleocharis achenes
Photos by K. Chayka and Peter M. Dziuk taken in Anoka and Ramsey counties.
Have you seen this plant in Minnesota, or have any other comments about it?