Listera auriculata Wieg.
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Basis for Listing
Although many orchids of the genus Listera are familiar and widespread, L. auriculata is poorly known and has a very limited distribution. It is rarely encountered and, until recently, little was known about its distribution and habitat requirements. The species is very rare in Minnesota, prompting its listing as a state endangered species in 1996. Its persistence is precarious because there are so few populations and most populations have few individuals. Habitat destruction related to high water levels and vegetation succession, either by human alteration or by natural processes, is a potential threat.
Listera auriculata produces a flowering stem 10-20 cm (4-8 in.) high with small distinctive flowers that necessitate a close examination for positive identification. Flowers are pale green with 3 sepals and 3 petals. The lower petal is modified into a broad lip that is dilated near the summit. The lip is cleft 1/4 to 1/3 its length and auricled at the base. There is a single pair of opposite, ovate, sessile leaves. Two other species of Listera occur in the state. One of these, L. cordata, is similar but the lip is not dilated above. Listera convallarioides is also similar and does have a dilated lip, but the base in not auricled.
In the Great Lakes region, L. auriculata is reported to colonize sites near the mouths of streams, above the normal high-water line, either in sand under Alnus spp. (alders) or on mossy banks under forest trees (Case 1964). In Minnesota, it is characteristically found along streams or pond margins in low, moist hardwood forests, mixed hardwood-coniferous forest, and shrub swamps. It is also found on the bedrock and gravel shores of Lake Superior. These are typically shady, mossy, acidic habitats on alluvial deposits or on shallow, organic soil. The collection record indicates L. auriculata most often occurs in rather small, transient colonies. Most populations recorded in Minnesota have only a few individuals; only occasionally is a large population found (Smith 1993).
Biology / Life History
Listera auriculata is a short-lived perennial that reproduces entirely by seed. Seeds are dispersed by gravity, and over short distances by wind. Flowers are pollinated by small flying insects. This species is believed to be mychorrhizal, but the specific fungal host is not known. Observations suggest that within a population, the numbers of plants and the number of plants in flower can vary greatly from year to year.
Conservation / Management
Because so little is known about L. auriculata in Minnesota, threats to its survival are difficult to evaluate. Populations need to be monitored long-term to provide better tracking and life history information. Many populations are quite small and vulnerable and seem to be linked to natural ecosystem processes such as seasonal flooding and vegetation succession, although the nature of the link is not clear. It is clear that certain habitat parameters must be maintained, particularly the natural hydrologic regime, and tree canopy structure. These parameters could be compromised by canopy removal or grading activities within the immediate watershed.
Conservation Efforts in Minnesota
Most sites supporting L. auriculata are in public ownership, which raises possibilities for conservation actions, although no specific actions have been taken to date. One population is in a state Scientific and Natural Area.
References and Additional Information
Case, F. W., Jr. 1964. Orchids of the Western Great Lakes Region. Cranbrook Institute of Science Bulletin Number 48. Bloomfield Hills, Michigan. 251 pp.
Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis, Minnesota. 320 pp.
Smith, W. R. 1993. Orchids of Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 172 pp.
U.S. Forest Service. 1999. Population viability assessment in forest plan revision. Statement of purpose and reason. Draft species data records: Listera auriculata. United States Forest Service, Region 9.