Rare Species Guide

  Basis for Listing

Carex hookerana (Hooker’s sedge) is considered a rare or uncommon species throughout most or all of its range, which centers on the Upper Great Plains. Although it has been known from nearby North Dakota for some time, it was not known to occur in Minnesota until 2005, when it was discovered at a single site in Becker County (Laurentian Mixed Forest Province). The occurrence is in a grassland habitat, with a history of low-intensity agriculture, and consists of about 25 plants. Subsequently, another small population was found in an oak savanna in Marshall County (Tallgrass Aspen Parklands Province). Given the documentation of only two populations, the small size of those populations, and the potential need for active management to maintain habitat conditions as well as the need to clarify the species’ abundance and distribution in the state, Carex hookerana was listed as special concern in 2013.

In 2014, two plants were found growing in a livestock pasture in Fillmore County in southeastern Minnesota. Those plants are likely an unintentional introduction that may or may not persist. Because of their unknown origin and rather artificial habitat, these plants have no role to play in the conservation of the species in Minnesota.

  Description

Field recognition: Carex hookerana can form dense clumps of long, narrow leaves and arching culms. Nothing about it will stand out until details of the spikes are examined. First, the scales are about the same length and width as the perigynia and neatly cover them. The scales are fragile and pale in color, with a narrow green midrib that often continues as a stout awn. Next, notice the perigynia: at maturity they are unusually translucent, almost transparent, allowing the achene inside to be easily seen. Carex hookerana is perhaps vaguely similar in aspect to C. deweyana (Dewey's sedge; sec. Deweyanae) or C. siccata (dry spike sedge; sect. Ammoglochin); however, any resemblance is only superficial.

Technical description: Culms loosely cespitose, lax, 20–80 cm long. Rhizomes to 3 cm long or not discernible. Leaves to 2.5 mm wide, equaling or exceeding the culms in length; dorsal surface of sheaths uniformly colored between veins, not cross-veined. Inflorescence 2–3.5 cm long, simple. Spikes androgynous, 5–10 per culm, continuous and overlapping or the lowermost somewhat separate, with 3–10 erect perigynia each. Pistillate scales 2.7–3.6 mm long, acuminate or awned, the body at least as long and as wide as the perigynia. Perigynia glabrous, ovate to elliptic, 2.6–3.5 mm long, 1–1.5 mm wide, translucent at maturity, veinless; base with a small pulpy or spongy portion; apex contracted or tapered to a serrulate bidentate beak 0.6–1.2 mm long. Achenes biconvex; style deciduous. Maturing mid-June through late July.

  Habitat

In general, C. hookerana is a prairie species, or at least it occurs primarily in that portion of North America where grasslands are the dominant landscape feature. Within the general grassland biome, C. hookerana shows some affinity to both prairies and oak savannas (Quercus macrocarpa), and possibly oak groves. The fidelity and nature of the affinity is unclear. Soils are expected to be sandy or sandy-loam and somewhat droughty. Exposure is full sunlight or partial shade.

  Biology / Life History

Carex hookerana is a long-lived perennial that reproduces exclusively by seed. Based on characteristics of the genus, pollination is likely mediated by wind, and the species is probably self-compatible. The seeds possess no specialized structures for dispersal; they likely rely on gravity and wind gusts for short-range dispersal. Long-range dispersal, to the extent it happens at all, is likely a result of incidental and episodic transport by animals, most likely small mammals and birds. The close association of C. hookerana with prairie and bur oak (Quercus macrocarpa) would imply an adaptation to wildfire. It also seems likely that C. hookerana is adapted to periodic drought.

  Conservation / Management

Because of the comparatively recent discovery of this species in Minnesota, there has been little opportunity to observe population trends or response to management. That said, a few general guidelines may prove useful. Clearly the habitat of C. hookerana should be maintained, protected, and enhanced if possible. Shade, resulting from encroaching trees or shrubs, should be addressed by mechanical cutting or dormant season burns. Livestock grazing should be prohibited, at least until the extent of a population can be determined.

  Best Time to Search

Mature perigynia are needed for the reliable identification of C. hookerana. This is expected to be during the month of July and the first two weeks of August.

  Authors/Revisions

Welby R. Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Ball, P. W. 2002. Carex. sect. Phaestoglochin. Pages 285-297 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 23. Oxford University Press, New York New York.

Ball, P. W., and A. A. Reznicek. 2002. Carex. Pages 254-572 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 23. Oxford University Press, New York, New York.

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.

Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the prairie parkland and tallgrass aspen parklands provinces. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 362 pp.

NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia.

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