Eleocharis wolfii (Gray) Gray ex Britt.
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Basis for Listing
Of all the Minnesota spike-rushes, Eleocharis wolfii (Wolf's spikerush) may be the rarest and most poorly understood. In fact, it is surprisingly rare for a species with such wide distribution, but it seems to be rare or infrequent throughout its range. Eleocharis wolfii was first collected in Minnesota in 1892 by A. L. Ballard somewhere near Nicollet in Nicollet County. It was next found in 1921 near Lake Traverse in the Red River Valley and again in Norman County in 1967. None of these sites have been relocated since the dates of their original discovery, and it is unknown if any of these populations still survive. In 1998, the Minnesota Biological Survey discovered E. wolfii growing on the margins of ephemeral rainwater pools on Jordan sandstone outcrops along the Minnesota River in Scott County. As of 2008, it had also been located on the margins of rock pools at one location along the Minnesota River in Renville County and in three locations on Sioux quartzite outcrops in Pipestone and Rock counties.
Eleocharis wolfii appears to have always been rare, but it has likely suffered a recent decline resulting from loss of habitat; specifically, the loss of native grasslands and wetlands owing to agricultural expansion. The amount and rate of decline cannot be documented because there are too few records to detect a clear trend. However, it is possible to document the loss of wetlands, which has been as great as 90% in some agricultural regions. Eleocharis wolfii was listed as an endangered species in Minnesota in 1984.
Eleocharis wolfii is a small grass-like plant that commonly grows in small tufts. It is a perennial and spreads from slender rhizomes. Stems are 10-30 cm (4-12 in.) long and 1.0-1.1 mm (0.04 in.) wide, very flat, and slightly twisted. There are 2 leaf sheaths on the stem, the mouth of the uppermost sheath is free and loose, pointed, colorless or white, and membranous. Floral scales are acute, 2.5-3.3 mm (0.1 in.) long; the apex is acute, not notched. Perianth abristles are absent. Achenes are trigonous to nearly round in cross-section, 0.7-0.9 mm (0.03-0.04 in.) long (excluding tubercle), the surface has numerous horizontal rows of fine raised lines between prominent vertical ridges barely visible at 10x. The tubercle is distinct from the achene and variable in shape (Smith, 2018).
Eleocharis wolfii is most likely to be confused with E. compressa (least spike-rush). This is because of the flattened and twisted stems exhibited by both species and their propensity to occur together. Although E. compressa does have a somewhat flattened or "compressed" stem, as its name implies, it does not compare with the truly flat, ribbon-like stem of E. wolfii. Also, the achenes of E. wolfii are whitish rather than bright golden yellow, and the surface is lined rather than honeycombed. In the absence of mature achenes, check the floral scales. Those of E. compressa are notched; those of E. wolfii are not. Another feature to note is the uppermost of the two leaf sheaths, which is a tube-like structure that wraps around the culm some distance above the base of the stem. In the case of E. wolfii, the top of the sheath fits loosely around the culm; it is white and membranous and prolonged to a pointed tip. In E. compressa it is a tight truncated structure, with a darkened and thickened rim (Smith, 2018).
The preferred habitat of E. wolfii in Minnesota is poorly known, and more research is needed. Historical collections refer to its habitat only as moist places. The site in Norman County was described as mud flats near a stream. Presumably, these were wetlands in the prairie region. The populations in Renville, Scott, Pipestone, and Rock counties were associated with rock outcrops, specifically the margins of bedrock pools that collect or concentrate precipitation run-off.
Reports from the rest of its range indicate that E. wolfii occurs in marshes, swamps, sedge meadows, wet to wet-mesic prairies, wet margins of lakes, rivers, ponds and creeks, wet ditches, sandy roadsides, mud flats, and ephemerally wet flatwoods. It is reported that its best growth and reproduction is seen in relatively open, sunny locations that remain moist throughout the growing season (NatureServe 2008).
Biology / Life History
Eleocharis wolfii is a perennial grass-like species that commonly grows in clumps and forms mats. It spreads by well-developed underground stems. Leaves are reduced to bladeless sheaths confined to the base of the plant. Both stems and leaves function as photosynthetic organs. Flowering and fruiting occur from May through July. The species requires high light levels to produce viable seed. Without such light the plants become weakened and elongated, and the seeds abort before maturity (NatureServe 2008).
Conservation / Management
The loss of native grasslands and wetlands in North America is the greatest threat to E. wolfii. Activities such as wetland draining and conversion of native prairie to agricultural crops, residential developments, and road construction are responsible for this loss. Grassland habitats are also sometimes threatened by the overgrowth of woody vegetation that has resulted from the loss of natural fires. Other threats include invasion of non-native plants, soil compaction and trampling by livestock, destructive recreational activities, and herbicide application (NatureServe 2008).
Any management considerations for this species should include the protection of natural hydrological regimes and the judicious use of prescribed fire in prairie habitats. Regular monitoring of known sites should occur, as well as efforts to relocate historic sites and survey potentially suitable habitat. Any proposed development in the vicinity of known E. wolfii populations, or activities that would disrupt the hydrological system, should be examined carefully and modified to avoid any adverse impacts (NatureServe 2008).
Best Time to Search
The best time to identify E. wolfii is when it is in fruit from mid-June through mid-July; however, the plant remains recognizable into late September.
Conservation Efforts in Minnesota
In 2007, the Renville and Redwood County Soil and Water Conservation Districts in association with state and federal agencies coordinated an initiative to compensate interested landowners for permanently protecting the most ecologically intact rock outcrops and associated wetlands in those two counties. A total of 86 ha (212 ac.) were enrolled into perpetual conservation easements as a result of this initiative, and E. wolfii is one of the rock outcrop species most likely to benefit from the program. In 2009, the program was expanded to protect an additional 214 ha (530 ac.) within a five county area of the Upper Minnesota River valley. Conservation plans, which outline conservation practices such as removal of invasive species and livestock exclusion, are being developed for each of the easement sites. Habitat maintenance and improvement measures such as prescribed burning, fencing, rotational grazing, and/or seeding are also included in the plans.
References and Additional Information
Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. Second Edition. New York Botanical Garden, Bronx, New York. 910 pp.
Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence, Kansas. 1,402 pp.
McKenzie, P. M., C. T. Witsell, L. R. Phillippe, C. S. Reid, M.A . Homoya, S. B. Rolfsmeier, and C.A. Morse. 2009. Status assessment of Eleocharis wolfii (Cyperaceae) in the United States. Journal of the Botanical Research Institute of Texas 3(2):831-854.
NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia.