Eleocharis rostellata (Torr.) Torr.
Basis for Listing
Eleocharis rostellata (beaked spikerush) is chiefly an inhabitant of salt marshes along the Atlantic Coast and highly specialized alkaline wetlands in the western part of the country. In the central part of the country, it is largely restricted to calcareous fens, spring fens, and exposed marly flats. Minnesota populations are similarly restricted to highly localized and vulnerable habitats and are widely disjunct from populations in other states. In fact, E. rostellata was first discovered in Minnesota in 1980, when these unique habitats were just beginning to be recognized. Eleocharis rostellata was listed as a threatened species in Minnesota in 1984.
There are 17 species of Eleocharis in Minnesota. They are all rather similar in appearance and can be difficult to tell apart. Each member of the genus produces a single spikelet at the top of a naked stem. The leaves have been reduced to 2 bladeless sheaths near the bottom of the stem. Eleocharis rostellata can be distinguished by its formation of dense tussocks, its long firm flattened culms, and the presence of sterile (non-flowering) culms that may be more than 1 m (39 in.) long and which may arch back to the ground and take root at the tip. This vegetative feature is unique but may not always be present, so the spikelet is necessary for positive identification. Scales of the spikelet are drab or brownish, and the tips are pointed. The 3-sided achene (one-seeded fruit) has a pyramidal cap (tubercle) that is flush (confluent) with the sides of the achene. The achene is 1.3-1.8 mm (0.05-0.07 in.) long (excluding the tubercle), which is comparatively large for a member of this genus.
Technical Description: Plants perennial. Culms compressed or nearly round in cross-section, firm, densely cespitose, 20--100+ cm 8-39 in.) long, 0.6--2 mm (0.02-0.08 in.) wide, erect or the longer culms arching and tip-rooting in late summer. Rhizomes short or not apparent. Leaves 2 per culm, reduced to bladeless sheaths; summit of distal sheath oblique, the rim darkened and thickened. Spikelet ovoid to lanceoloid, normally 6--20 mm (0.2-0.8 in.) long, 2--4 mm (0.08-0.2 in.) wide, with 15--40 flowers, rudimentary on tip-rooting culms. Floral scales predominantly brown to pale brown; base of lowest scale completely encircling the culm. Perianth bristles 5, about equaling the height of the tubercle or shorter. Achenes greenish to brown, trigonous, 1.3--1.8 mm (0.05-0.07 in.) long (excluding tubercle), 1--1.2 mm (0.04-0.05 in.) wide; surfaces appearing ± smooth or somewhat wrinkled at 30x. Tubercle beak-like, confluent with achene, to 1 mm (0.04 in.) long. Maturing early July to late August (Smith 2018).
All known Minnesota populations of E. rostellata occur in fens that are maintained by the surface discharge of calcareous or circumneutral groundwater. This habitat type is very rare compared with the other wetland types in Minnesota. Most wetlands, such as marshes and lakeshores, receive their water from rainfall and from surface water draining from higher elevations. Other wetlands, such as the vast expanses of acidic, mineral-poor peatlands in the forested region are even more dependent on rainwater. Only wetlands fed by mineral rich groundwater support E. rostellata. The habitat type has been described as a calcareous fen in the prairie region and as a spring fen in the northern forested region of Minnesota. In all cases, these specialized wetlands are sunny, cold, oxygen-poor, peat-filled habitats dominated by low-growing sedges and mosses.
Biology / Life History
Eleocharis rostellata is a member of the sedge family. It is a perennial plant that forms persistent clumps. In addition to producing normal flowering culms, it may produce special, sterile (non-flowering) shoots that can assist in the vegetative spread of the plant by rooting at the tip and forming a new green shoot. It also reproduces sexually by the production of seeds (achenes). The seeds are small, less than 2 mm (0.08 in.) long and are dispersed during July and August. Dispersal is considered passive in that no active agent, such as a bird, mammal, or insect is known to play a role. Seeds are normally produced every year, but individual plants are long-lived, and they are not dependent on a viable crop of seeds being produced each year to sustain the population.
Conservation / Management
The conservation of E. rostellata in Minnesota is tied to the conservation of its specialized fen habitat. A typical calcareous fen may be only 2 ha. (5 ac.) in size, but the recharge area that maintains its groundwater supply may cover thousands of hectares. Spring fens similarly are recharged over thousands of acres of habitat. Without safeguarding the hydrologic settings of these fens, the security of this species' habitat is in doubt. Activities that could affect hydrologic systems include upslope gravel mining and withdrawal of large volumes of water from the aquifers that feed the fens. There have been significant losses recently, especially in the prairie region, resulting from diverted groundwater flows.
After years of fire suppression, shrub cover in some fens may become so dense that it threatens populations of E. rostellata. The restoration of a dormant-season fire regime that mimics natural wildfires may not be enough to control shrubs. In such cases, physical shrub removal may be the best alternative. Woody encroachment should be controlled by hand, preferably when the ground is frozen. Because of the fragile nature of the peat layer that supports the unique conditions of fens, use of tracked vehicles or other mechanized equipment should be avoided.
Best Time to Search
The best time to search for Eleocharis rostellata is when the achenes are ripe, from early July to late August.
Conservation Efforts in Minnesota
Understanding the distribution and habitat preferences of E. rostellata has been greatly enhanced by systematic inventories of calcareous fens and spring fens conducted by Minnesota DNR botanists. These inventory efforts have been ongoing since the 1980s. At least two populations of E. rostellata that occur in spring fens and one population that occurs in a calcareous fen are in state Scientific and Natural Areas, and several of the calcareous fen populations are on public land. However, no formal mechanism exists to assure the hydrologic integrity of aquifers that feed most of these areas. The broader challenge remains understanding how land use changes outside the boundaries of protected areas may affect critically important hydrologic conditions within the protected areas.
Welby R. Smith (MNDNR), 2023
(Note: all content ©MNDNR)
References and Additional Information
Glaser, P. H. 1983. Eleocharis rostellata and its relation to spring fens in Minnesota. The Michigan Botanist 22:19-21.
Smith, S. G., J. J. Bruhl, M. S. Gonzalez-Elizondo, and F. J. Menapace. 2002. Eleocharis. Pages 60-120 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 23. Oxford University Press, New York, New York.
Smith, W. R. 2018. Sedges and rushes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 696 pp.
Svenson, H. K. 1934. Monographic studies in Eleocharis III. Rhodora 36(431): 377-389.