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

The stems of C. hookerana are clumped and can reach 80 cm (32 in.) in length; rhizomes are short or not apparent. The leaves are no more than 2.5 mm (0.10 in.) wide and shorter than the stems. The inflorescence is 2-5 cm (0.75-2.0 in.) long and consists of 5-10 individual spikes. Each spike has both male and female flowers, with the female flowers located above the male flowers. At maturity, each spike will have 5-10 perigynia. The perigynia are 2.6-3.5 mm (0.10-0.14 in.) long and 1.1-1.2 mm (0.04-0.05 in.) wide; each perigynia is covered by an ovate scale that is both longer and broader than the perigynia (Ball and Reznicek 2002). Since identification of species in the genus Carex can be difficult, it is advisable to seek confirmation from a specialist.

  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.