Basis for Listing

Scleria verticillata is a slender sedge that is generally rare or local throughout the northern part of its range, where it is a strict calciphile. Its unusual and restrictive habitat requirements limit the species to a rare native plant community called a calcareous fen. Calcareous fens are localized, fragile wetlands that depend on specific hydrologic and geologic conditions, and are themselves unique and quite rare in Minnesota. In certain places on the landscape, cold, calcium-rich (or calcium/magnesium-rich) groundwater seeps to the surface. In places where the seepage has remained uninterrupted for thousands of years, plant remains have accumulated and peat has formed. This habitat type and the plant community that evolved with it is called a calcareous fen.

Before the 1850s, there may have been as many as 2,200 ha (5,436 ac.) of calcareous fen habitat just in the Lower Minnesota River valley between Mendota and Shakopee. Human activities have reduced the total to fewer than 40 ha (99 ac.). The other major concentration of calcareous fen habitat is along the ancient beach ridges of Glacial Lake Agassiz in northwestern Minnesota. Most of the calcareous fens in that region have now been destroyed by agriculture, gravel mining, and water management projects (draining or impoundment).ver

The decline in acreage of calcareous fen habitat has been closely paralleled by a decline in S. verticillata. The northwestern-most populations of S. verticillata occur in Becker and Mahnomen counties as scattered remnants of a much larger and continuous occurrence that has been fragmented by agriculture. Many populations south of the Twin Cities have been lost to development and those than remain are isolated from one another by roads and degraded habitat. Intensive field surveys in the 1980s and 1990s located a few new records of S. verticillata, but these are similarly threatened. Scleria verticillata was listed as a threatened species in Minnesota in 1984.

  Description

Scleria verticillata is a slender annual that may be very difficult to detect when it is growing among other sedges and grasses. It has fine, linear leaves no more than 2 mm (0.08 in.) wide. It has 2-6 flower clusters spaced apart from one another on the main stem. Each tiny flower has a long-pointed scale and each cluster of flowers has an inconspicuous bract. An obvious field character is the white, stone-like achene (a kind of one-seeded fruit). The achene is rough with transverse ridges and a blunt disk area where the achene was attached to the plant (Core 1936). The technical characters that distinguish this genus from other sedges are not obvious. It is not in the genus Carex because the achene is not in a little sac, and few other sedge-like plants have a white achene. The only other member of the genus Scleria in Minnesota, S. triglomerata (tall nut-rush), is also a rare species but it is much larger, the stem is strongly triangular in cross-section, and it does not occur in calcareous fens.

  Habitat

Scleria verticillata is entirely restricted to calcareous fens in the prairie regions of Minnesota, and seems to occur only in the better quality, least disturbed examples of this specialized plant community. It has never been found in the spring fens or ribbed fens that sometimes occur in the large peatland complexes of the forested regions of the state. Within calcareous fens, S. verticillata acts as a pioneer species on exposed marl and along the margins of shallow pools. Conditions there are quite severe, with a very high pH and high mineral content. Scleria verticillata is usually found in association with other strict fen species such as Rhynchospora capillacea (hair-like beak-rush) and Carex sterilis (sterile sedge).

  Biology / Life History

Because S. verticillata is an annual, its reproduction depends entirely on seed production. It is not known how long seeds remain viable in the peaty substrate in a calcareous fen. The seeds are not adapted for wind dispersal but may be aided in transport by animals. Ridges on the achene might help them adhere to mud or marl and thus to birds feet. Or possibly, the plants are browsed or grazed and ingested achenes are deposited elsewhere.

It can be very difficult to see S. verticillata when mature fruits are not present, so searches are most effective if limited to the period between the middle of July and the middle of September.

  Conservation / Management

The conservation of S. verticillata in Minnesota is tied to conservation of the specialized calcareous fen habitat upon which it relies. A typical calcareous fen may be less than 2 ha (5 ac.) in size, but the recharge area that maintains its groundwater supply may cover thousands of hectares. Because of their dependence on delicate groundwater hydrologic conditions, calcareous fens can be indirectly affected by remote activities such as gravel mining or wetland drainage that occur several kilometers away. Without safeguarding the hydrologic regime of the entire system supporting calcareous fens, the security of this habitat, and therefore, S. verticillata is uncertain.

  Conservation Efforts in Minnesota

As part of a directed search effort for calcareous fens by the Minnesota DNR County Biological Survey, several previously unknown fens have been discovered, some of which harbor viable populations of S. verticillata. This major contribution to conservation offers a sound basis for establishing protection plans. Still remaining to be resolved, however, is the broader issue of how climate and land use changes may affect critically important hydrologic conditions occurring outside the boundaries of protected fens.

  References and Additional Information

Core, E. L. 1936. The American species of Scleria. Brittonia 2:1-105.

Reznicek, A. A., J. E. Fairey III, and A. T. Whittemore. 2002. Scleria. Pages 242-251 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. 1983. A range extension of Scleria verticillata in Minnesota. The Michigan Botanist 22:27-30.