Rare Species Guide

  Basis for Listing

Although Carex flava does not appear to have suffered from large-scale habitat loss or face a species-specific threat, it is clearly uncommon in Minnesota. What is perceived as a complex population structure that is dependent on dynamic ecological processes makes it difficult to assess the conservation needs and protection strategies for this species. Still, the status of C. flava in Minnesota deserves careful monitoring, which is the basis for its listing as a special concern species.

  Description

Carex flava is a perennial sedge with stems that grow to a maximum height of about 75 cm (2.5 ft.) and form a small but dense clump. The leaves are 2-5 mm (0.08-0.20 in.) wide and are usually shorter than the stems. The inflorescence consists of 2-4 spikes. The terminal spike is usually 1-2 cm (0.4-0.8 in.) long and male; the lateral spikes are usually a little shorter and are predominately female with a few male flowers at the tips. The scale that subtends each female flower has a green midrib and dark reddish-brown margins. The perigynia (the membranous coverings of the seeds) are 4-5.5 mm (0.16-0.22 in.) long and 1.3-2 mm (0.05-0.08 in.) wide, with a yellow body and a green or yellow beak. The beak is 1.6-2.5 mm (0.06-0.10 in.) long and comprises 40-50% of the total length of the perigynium. The distal half of the beak usually has short, stiff (scabrous) hairs and is usually reflexed when mature. Carex flava looks similar to C. viridula (green sedge) and C. cryptolepis (secretive sedge), but has wider leaves, larger perigynia, and the beaks of the perigynia are scabrous (magnification needed).

  Habitat

Carex flava occurs primarily at the margins of small rivers and streams that drain into Lake Superior, usually within a few miles of the lake itself. Many of the occurrences seem to be even further localized in seepy habitats that develop where the stream has cut through a confining strata of clay or bedrock and released a steady trickle of groundwater. The streams are typically in a matrix of northern hardwood forests or mixed conifer-hardwood forests, and the stream banks are sunny or partially shaded. The substrate is typically river sediments of one sort or another including sand, gravel, and silt, although one population was observed growing in moss mats anchored on bedrock ledges. The conditions are usually wet, with water saturating the substrate. Carex flava does not appear to grow emergent from more than perhaps an inch of water. Some of the sites appear to be above the normal high-water line of the stream and others appear to be below. One atypical population was found growing along a small fen within an old-growth cedar swamp. Carex flava has occasionally also been found in a variety of early successional habitats not associated with streams, such as roadside ditches and abandoned gravel pits. These sites of anthropogenic origin seem to have many of the same habitat features as streamside habitats, but without obvious mechanisms for the long-term maintenance of conditions favorable for this species.

  Biology / Life History

Carex flava is a perennial sedge that forms small but dense clumps of erect seed-producing stems. Based on the very short rhizomes, it is likely that reproduction is accomplished entirely by seed. Given the streamside habitat of C. flava, it also seems likely that the stream itself serves as a dispersal agent for the seeds, and possibly for entire plants. Since flooding and ice-scouring can dislodge entire plants and carry them downstream, it seems possible that they may, on occasion, become stranded on a bank and take root. Mechanisms for dispersing upstream are not as apparent, but may involve animal vectors, possibly birds or mammals. It appears that the seemingly isolated pockets of C. flava plants that occur along the reaches of a river may function as a single interacting metapopulation rather than as a series of isolated populations. Occurrences in roadside ditches, gravel pits, and other temporary habitats may be isolated from dispersal mechanisms and therefore not contributors to any functional metapopulation.

The best time to search for C. flava is when mature perigynia are present from mid-July through mid-September.

  Conservation / Management

Carex flava occupies a dynamic, albeit unstable, transitional habitat along the margins of rather steep gradient streams. There seems little that can be done to enhance the chances of survival for C. flava other than maintaining the natural contours, slopes, and flows of the streams where C. flava occurs, and protecting the hydrology of fen communities.

  Conservation Efforts in Minnesota

No known conservation efforts have been directed towards this species in Minnesota.

  References and Additional Information

Crins, W. J. 2002. Carex sect. Ceratocystis. Pages 523-527 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 23. Oxford University Press, New York, New York.

Schmid, B. 1984. Life histories in clonal plants of the Carex flava group. The Journal of Ecology 72(1):93-114.

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