Rare Species Guide

  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.

Most of the extant populations in Minnesota occur at the margins of shallow pools on level bedrock outcrops in the southern part of the state (Minnesota River Prairie and Inner Coteau subsections). It seems likely that they also occurred in prairie wetlands in pre-settlement times.

Although E. wolfii appears to have always been rare, it has likely suffered a recent decline resulting from loss of habitat; specifically, the loss of shallow prairie wetlands owing to agricultural expansion. The amount and rate of decline of E. wolfii cannot be known for sure, because there are too few records to detect a clear trend. However, the loss of wetland habitats has been documented and exceeds 90% in some agricultural regions. Eleocharis wolfii was listed as an endangered species in Minnesota in 1984.

  Description

Eleocharis wolfii is most likely to be confused with E. compressa (flattened spikerush). This is because of the flattened and twisted culms exhibited by both species and their propensity to occur together. Although E. compressa does have a somewhat flattened or “compressed” culm as its name implies, it does not compare with the truly flat, ribbon-like culm of E. wolfii. Also, the achenes of the two species are quite different. Those of E. compressa are yellow with a honeycombed surface; those of E. wolfii are whitish with faint horizontal lines and bold vertical ridges. In the absence of mature achenes, check the floral scales. Those of E. compressa are notched, those of E. wolfii are not (Smith 2018). 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 culm. 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. 

Technical Description: Plants perennial. Culms distinctly flattened in cross-section and usually twisted, 10--30 cm (4-12 in.) long, 0.5--1.1 mm (0.02-0.04 in.) wide. Rhizomes soft, slender. Leaves 2 per culm, reduced to bladeless sheaths; mouth of distal sheath free and loose, pointed, colorless or white, membranous. Spikelet 2--8 mm (0.08-0.3 in.) long, 1--3 mm (0.04-0.12 in.) wide, with 15--30 flowers. Floral scales 2.5--3.3 mm (0.01-0.13 in.) long; predominantly or entirely whitish, or with red-brown flanks; apex acute, not notched. Perianth bristles absent. Achenes pale yellowish green to whitish, trigonous to nearly round in cross-section, 0.7--0.9 mm (0.03-0.04 in.) long (excluding tubercle), 0.4--0.5 mm (0.02 in.) wide; surface with numerous horizontal rows of fine raised lines between prominent vertical ridges barely visible at 10x. Tubercle distinct from achene, variable in shape, 0.1--0.2 mm (0.004-0.008 in.) high, 0.1--0.2 mm (0.004-0.008 in.) wide. Maturing early June to early July (Smith 2018).

  Habitat

With one exception, the known habitats of E. wolfii in Minnesota are associated with level outcrops of bedrock within a prairie or savanna setting. Specifically, the margins of shallow rain water pools that form in depressions on the bedrock or in thin sediments over the bedrock.

The one exception is a small population in Morrison County that occurs in a wet meadow in deep sandy soil (Anoka Sand Plain Subsection). The water table is very near the surface, possibly creating a habitat that is ecologically equivalent to rock pools. All the known habitats seem to present harsh growing conditions with a shallow or nutrient-poor rooting zone where water levels fluctuate unpredictably. Such conditions usually favor small low-growing species with a short or accelerated seasonal cycle.

Reports from its range outside Minnesota indicate that E. wolfii occurs in habitats variously described as marshes, wet to wet-mesic prairies, wet margins of lakes, rivers, ponds and creeks, wet ditches, sandy roadsides, mud flats and ephemerally wet flatwoods. All seem to describe shallow transitional wetlands or ecotones in sunny settings (NatureServe 2020).     

  Biology / Life History

Eleocharis wolfii is a wind-pollinated, perennial sedge. It spreads short distances by the growth of rhizomes (underground stems). Leaves are reduced to bladeless sheaths confined to the base of the plant. Both stems and leaf sheaths function as photosynthetic organs. Flowering and fruiting occur from May through early 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 2020). The seeds (achenes) possess no specialized dispersal structures and likely move short distances by wind, gravity, and possibly the foraging activity of insects or small mammals.

  Conservation / Management

Considering range-wide trends, the loss and degradation of native grasslands and wetlands is probably the greatest threat to E. wolfii. Activities such as wetland draining, conversion of native prairie to agricultural crops, residential developments, and road construction are responsible for most of this loss. Grassland habitats are also sometimes threatened by the overgrowth of woody vegetation that has resulted from the absence of natural fires. Other threats include invasion of non-native plants, soil compaction and trampling by livestock, destructive recreational activities, and herbicide application (NatureServe 2020).

The typical micro habitat of E. wolfii in Minnesota occurs on bedrock, which is not easily converted to human uses. Quarrying of bedrock does occur in Minnesota but is not widespread in southern Minnesota where E. wolfii is likely to be found. With little other economic use for rocky prairie land, landowners will often graze cattle. Although cattle find very little to eat on bedrock, they still cause problems by damaging the delicate moss and lichen communities that characterize E. wolfii habitats, they foul the water and the thin sediments that form the rooting zone for the plants, and they spread the seeds of non-native weeds.

  Best Time to Search

The best time to identify Eleocharis wolfii is when it is in fruit from early June through early July; however, the plant remains recognizable into late September.

  Conservation Efforts in Minnesota

A number of E. wolfii sites occur on sites owned by The Nature Conservancy and the state Scientific and Natural Area program, which afford the species the highest level of conservation. In addition, 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. In 2009, the initiative was expanded to encompass five counties in the Upper Minnesota River Valley (Protection of Granite Rock Outcrop Ecosystem). By 2012, approximately 227 ha (560.4 acres) 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. Conservation plans, which outline conservation practices, such as removal of invasive species and livestock exclusion, were developed for each of the easement sites. Habitat maintenance and improvement measures, such as prescribed burning, fencing, rotational grazing, and/or seeding were also included in the plans.

  Authors/Revisions

Welby R. Smith (MNDNR), 2020

(Note: all content ©MNDNR)

  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.

Harris, F. 2009. Rock pools on the prairie: ephemeral pools on the prairie form amazing mini-ecosystems. Minnesota Conservation Volunteer 72(423):30-39.

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. 2020. NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. <https://explorer.natureserve.org/Search>. Accessed 21 April 2020.

Smith, W. R. 2018. Sedges and rushes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 696 pp.