Eleocharis wolfii (Wolf's Spikerush)
|Also known as:
|sun; moist to wet; wet meadows, marshes, muddy shores, ephemeral pools in rock outcrops
|July - September
|4 to 16 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, mostly pointed at the tip, 3 to 9 mm (to ~1/3 inch) long, with 15 to 30 florets spirally arranged, each floret subtended by a single scale. Scales are 2.5 to 3.5 mm long, pointed at the tip, purple-brown to orange-brown to straw-colored with a green to straw-colored midrib and white, translucent edging. Florets have 3 stamens and a 3-parted style. The lowest scale in the spike is similar to the rest but may be more leathery, and lacks a flower.
Leaves and stems:
The 2 leaves are bladeless and reduced to sheaths on the lower stem. The upper sheath is thin, papery and fragile, whitish to reddish toward the base, slightly expanded and loosely wrapping the stem at the tip, splitting and V-shaped to shredded on the back, pointed at the tip on the front, and lacks a distinct tooth at the apex.
Stems are flat, rectangular in cross-section, 1 to 1.5 mm wide, smooth or with 1 to several vertical ridges, and are often spirally twisted. The edges typically roll in as stems dry. Stems are mostly erect, sometimes prostrate, may be single but usually form small clumps, and often form mats 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 .7 to 1.1 mm long, .4 to .5 mm wide (about twice as long as wide), brown to grayish-white, have 9 to 13 vertical ridges with numerous cross-bars, are slightly compressed 3-sided to nearly round in cross-section, narrowly urn-shaped in outline, rounded at the tip end and tapering at the base. Tubercles are greenish to brown, pyramidal to depressed, .1 to .2 mm long, as wide as or wider than long. A short neck/constriction exists between the tip of the achene and the base of the tubercle. There are no bristles surrounding the base of the achene.
Eleocharis wolfii is one of the rarest Spikerushes in Minnesota, where it reaches the northern tip of its US range. While it may be found in a variety of wet places such as marshes, mud flats, wet ditches, and receding shores, in Minneosta it has nearly always been associated with pools in rock outcrops, both sandstone and quartzite. According to the DNR, it has probably always been rare but has likely become more so due to habitat loss from agriculture. It was listed as a MN Endangered species in 1984 and is also listed as Endangered in Wisconsin.
E. wolfii superficially resembles some other colony-forming Spikerushes, but is most easily distinguished by the distinctly flattened stems that are often twisted, the thin, fragile sheaths that are loose around the stem and pointed at the tip on the front, and achenes nearly round in cross-section with 9 to 13 vertical ridges and numerous cross-bars. Most similar, with nearly identical achenes, is Eleocharis acicularis, which is very common in the state, has stems not more than .5mm wide, mostly round in cross-section and not twisted, the sheath is rounded at the tip not pointed, and floral scales are only 1.5 to 2.5 mm long. Also similar is Eleocharis compressa, which has compressed and twisted stems, but has a deep notch at the tip of scales, achenes are yellow-orange with a fine network pattern (not in rows), and the sheaths are more membraneous, tightly wrap the stem, and not shredding.
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- Eleocharis wolfii plants
- Eleocharis wolfii plants
- Eleocharis wolfii rock outcrop habitat
- straw-colored scales
- mature spike shedding scales and achenes
- (a bit fuzzy) close-up of sheaths
- comparison of Minnesota's Eleocharis achenes
Photos by K. Chayka and Peter M. Dziuk taken in Scott County.
Have you seen this plant in Minnesota, or have any other comments about it?