Scleria triglomerata Michx.
Basis for Listing
Scleria triglomerata (tall nutrush) is most abundant in the Atlantic and Gulf coastal regions of the eastern U.S., but it does range as far northwest as Minnesota. It is quite local and often rare in the Midwest and along the northern periphery of its range (Core 1936). This is especially true in Minnesota and adjacent states where the species is currently suffering a decline associated with loss of habitat. Scleria triglomerata was first discovered in Minnesota in 1881, followed by a couple records from 1925 to 1943. All were from portions of what are now the Minneapolis-St. Paul metropolitan area, and all are believed to have been destroyed by urban expansion, the last one in 1960. Intensive searching for remnant sandplain habitats (prairies, savannas and shallow wetlands) commenced in the late 1970s and continues to this day. This has resulted in the discovery a handful of sites that appear to support small but viable populations of S. triglomerata. All are in relatively intact remnants of native sand savanna habitats. Because of the intrinsic rarity of this species and the well-documented decline of its habitat and populations, S. triglomerata was listed as an endangered species in Minnesota in 1984.
Scleria triglomerata stands about knee-high and forms dense clumps. The stems are sharply triangular in cross-section; the leaves and bracts are stiff and erect. The flowers are in 3 spikey-looking clusters called glomerules (hence the Latin epithet) and produce only a few seed-like achenes. The achenes are more or less spherical, have a smooth white enamel-like surface, and sit on a short 3-sided pedestal-like base. Although the achenes are quite small, they are not concealed and can often be seen at some distance. If achenes are not present, look at the bases of the stems for overlapping and bladeless reddish sheaths. Enclosed in the lowest sheath of each stem is a hard, swollen base
Technical description: Plants perennial. Culms cespitose, 30--80 cm (12-32 in.) long, coarse, sharply triangular in cross-section, scabrous. Rhizomes developing into coarse nodulose clusters to about 8 cm (3 in.) across. Leaves: sheaths often hairy on ribs; basal sheaths reddish or reddish brown; upper sheaths pale; blades 2.5--6 mm (0.1-0.2 in.) wide, strongly ribbed, erect or stiffly ascending, not surpassing the inflorescence, scabrous and sometimes hairy on margins and midrib. Inflorescence terminal and often axillary, typically with 3 compact glomerules; bracts leaf-like, erect, easily surpassing the inflorescence. Spikelets 3--10 per glomerule; each with fewer than 12 unisexual flowers, including either male and female flowers or just male. Floral scales with scabrous awns. Achenes white or whitish, 2--3 mm (0.08-0.1 in.) long, ± spherical; surfaces smooth; bases trigonous, stipe-like, papillose. Maturing mid-July through September (Smith 2018).
All Minnesota populations of S. triglomerata occur in remnant examples of native sand savannas on, or closely associated with, the Anoka Sandplain. Specific conditions that are required to sustain populations are usually associated with small wet swales or wet meadows that are influenced by a shallow water table. Soils are typically sandy, though there may be a thin layer of organic material on the surface. The rooting zone is usually wet or moist in the spring but typically dry by mid-summer. Such conditions are most often found along the moisture gradients that circle shallow depressional wetlands or swales, though the gradients may be slight and difficult to see.
Biology / Life History
Scleria triglomerata is a perennial that reproduces only by seeds, which are dispersed short distances by gravity and perhaps wind or the actions of small ground-foraging animals. Long-distance dispersal likely happens infrequently and may be mediated by seed-eating birds. Like most sedges and grasses, this species does not produce showy flower parts for attracting insect pollinators; it is pollinated by wind. Recruitment is slow, so sustaining viable populations seems to rely on maintaining a low mortality rate.
Conservation / Management
Scleria triglomerata appears to be very persistent once established in a favorable setting. At least one population is known to have survived years of drought, spring flooding, and periodic prescribed fires in its savanna environs. Such environmental perturbations are normal in the natural habitat of this species and may, in fact, be essential to maintaining the plant community that supports this species. Since S. triglomerata seems unable to effectively colonize habitats that have been altered by human activities, the key to its survival in Minnesota is the conservation of high-quality native habitats where it is known to occur. The greatest threats to these habitats are land conversion, road building, off-highway-vehicles, and the invasive, non-native plant species that follow such activities. Favorable management activities can involve mechanical removal of encroaching woody plants and prescribed dormant-season fires.
Best Time to Search
The best time to search for Scleria triglomerata is from mid-July to September, when seeds are fully developed.
Conservation Efforts in Minnesota
One population of S. triglomerata is in Uncus Dunes State Scientific and Natural Area, another population is in the Santiago Oak Savanna Research and Natural Area in Sherburne National Wildlife Refuge in Sherburne County. A third population is in Helen Allison Savanna, a preserve of The Nature Conservancy. Current management regimes at these three sites seem to be conducive to the perpetuation of this species.
Welby R. Smith (MNDNR), 2021
(Note: all content ©MNDNR)
References and Additional Information
Core, E. L. 1936. The American species of Scleria. Brittonia 2:1-105. + illustrations.
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. 2018. Sedges and rushes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 696 pp.
Tryon, R. 1980. Ferns of Minnesota. University of Minnesota Press, Minneapolis. 176 pp.