Rare Species Guide

  Basis for Listing

Although many orchids of the genus Listera are familiar and widespread, L. auriculata (auricled twayblade) is poorly known and has a very limited distribution. It is found only in a narrow band of boreal and sub-boreal habitats in southeastern Canada and adjacent parts of the U.S. It is rarely encountered and, until recently, little was known about its distribution and habitat requirements. The species is very rare in Minnesota, occurring at only a few scattered spots in the northeast corner of the state (Northern Superior Uplands Section), which prompted 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.

  Description

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 (heart-leaved twayblade), is similar, but the lip is not dilated above. Listera convallarioides (broad-leaved twayblade) is also similar and does have a dilated lip, but the base is not auricled.

  Habitat

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 mesic 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 2012).

  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, though 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.

  Best Time to Search

The best time to search for Listera auriculata is when the plants are in peak flower, which is typically around the 4th of July.

  Conservation Efforts in Minnesota

Most sites supporting L. auriculata are in public ownership, which raises possibilities for conservation actions, though no specific actions have been taken to date. One population is in a state Scientific and Natural Area.

  Authors/Revisions

Welby R. Smith (MNDNR), 2020

(Note: all content ©MNDNR)

  References and Additional Information

Case, F. W., Jr. 1987. Orchids of the Western Great Lakes Region, revised edition. 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. 320 pp.

Smith, W. R. 2012. Native orchids of Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 400 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.