Scleria verticillata Muhl. ex Willd.
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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.
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.
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.
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.