Eleocharis macrostachya (Pale Spikerush)
|Also known as:||Large-spike Spikerush|
|Habitat:||sun; wet; ditches, swales, shores, marshes, wet meadows|
|Fruiting season:||July - September|
|Plant height:||4 to 40 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, 5 to 40 mm (to ~1½ inches) long, with 30 to 80 florets spirally arranged, each floret subtended by a single scale. Scales are 2 to 5.5 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 rounded at the tip, wraps 75-100% around the stem at the base, and lacks a flower. The second lowest scale is similar to the lowest and may or may not 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 and green to reddish towards the tip, straight across to concave on the back, the front rounded to blunt at the tip, often with an obscure to distinct tooth at the apex. Stems are erect, .5 to 2.5(3.5) mm diameter, round in cross section or more often compressed to 3 times as wide as thick, with up to 25 vertical ribs that become conspicuous when stems dry. Plants form colonies from long 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 1.1 to 1.9 mm long, .8 to 1.5 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 very short neck/constriction exists between the tip of the achene and the base of the tubercle. Usually surrounding the achene are 4 (rarely 5) barbed bristles, pale brown to whitish, much shorter than to about as long as the achene. Bristles are sometimes absent.
Eleocharis macrostachya 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. It is most similar to Eleocharis palustris and Eleocharis erythropoda, 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. macrostachya is the least common of the three, distinguished by: stems round in cross-section but usually compressed to 3 times as wide as thick, sheaths rounded to blunt at the tip on the front and often with an obscure to distinct tooth at the apex, the lowest scale on the spike wraps 70% or more around the stem, the second lowest scale may have a flower/fruit, achenes are smooth, brown and lens-shaped in cross-section, usually with 4 bristles varying from much shorter to about as long as the achene, and a whitish to dark brown cone-shaped tubercle 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 5.5 mm long with blunt to pointed tips. Magnification may be required to see some of these traits.
By comparison, both E. palustris and E. erythropoda sheaths usually lack a tooth at the tip and stems tend to be round in cross-section. On E. palustris, the lowest scale wraps less than 75% of the stem and the next lowest 1 or 2 scales lack flowers/fruit. On E. erythropoda, the lowest scale wraps 100% of the stem or nearly so, and the second lowest scale has a flower/fruit. 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 macrostachya plants
- Eleocharis macrostachya plants
- a mat of Eleocharis macrostachya
- wet ditch habitat
- 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 Kittson County. Photo by Keir Morse used under CC BY-NC-SA 3.0. ttps://calphotos.berkeley.edu/cgi/img_query?enlarge=0000+0000+0717+1565' rel='nofollow'>Photo by Zoya Akulova used under CC BY-NC 3.0.
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