Rare Species Guide

  Basis for Listing

The only evidence that Listera convallarioides occurs, or has occurred, in Minnesota is a herbarium specimen collected near Mineral Center (Cook County) in 1924. Efforts to find this species growing in the wild subsequent to 1924 have failed, although it must be stated that such efforts have been spotty and poorly organized. Because there is little reason to doubt the authenticity of the 1924 specimen, L. convallarioides is considered to be a native member of Minnesotas flora. Yet questions relating to its current distribution in the state, size of extant populations (if any), and threats to its survival remain unanswered. Listera convallarioides was listed as a special concern species in Minnesota in 1996.

  Description

Listera convallarioides is a small, delicate-looking orchid 11-27 cm (4.3-10.6 in.) tall. It has 2 leaves attached just above or near the middle of the stem. The leaves are sessile, subopposite, broadly ovate to elliptical or nearly circular in outline, 2.5-5.7 cm (1.0-2.2 in.) long, and nearly as wide. The flowering portion of the plant is a terminal raceme with 6-20 small, yellowish green flowers. The diagnostic portion of the flower is the prominent lip, a modified petal that projects forward. The lip is 9-12 mm (0.35-0.47 in.) long with a broad, shallowly notched apex. The lip is evenly tapered to the base except for a pair of lateral "bumps" about 1/8 of the way up from the base. An easier way to tell L. convallarioides from its closest look-alike, L. auriculata (auricled twayblade), is the lack of gland-tipped hairs on the pedicels and ovaries (Smith 2012). A hybrid between these 2 species has been reported in states and Canadian provinces east of Minnesota (Catling 1976).

  Habitat

The habitat description on the herbarium label of the only L. convallarioides specimen collected in Minnesota reads, "cedar-spruce-balsam forest". The tree species mentioned are known more widely as Thuja occidentalis (northern white cedar), Picea mariana (black spruce), and Abies balsamea (balsam fir). In northern Minnesota, this combination of tree species can be found in both uplands and in wetlands. A wetland with these species would be considered a swamp and would probably have weakly acidic surface water, peat soil, and a ground cover of Sphagnum spp. (sphagnum moss). In an upland situation, the forest would be moist and cool, but have no surface water, no peat, and no Sphagnum spp. In other parts of its geographic range, L. convallarioides occurs in both upland forests and wetland forests.

  Biology / Life History

Listera convallarioides is a short-lived perennial of wet or moist forests. The flowers are insect-pollinated and the seeds are wind and gravity dispersed. Reproduction appears to be entirely by seeds. In all probability, the plant would be shallowly rooted in living moss. It is even likely that the short roots of L. convallarioides would not penetrate into any substrate that could properly be called soil. This may make the plants vulnerable to prolonged or severe droughts. Flooding is normally a rare event in the type of habitat where we might expect to find L. convallarioides, and it would likely only occur for a relatively brief period when the snow melts in the spring. Listera convallarioides would be dormant during this period and would likely not be affected. Localized flooding from beaver activity is a different matter however. It is not seasonal in nature, and it may be relatively long-term in duration. This would likely prove fatal to L. convallarioides and most of the species normally associated with it.

The best time to search for L. convallarioides is when it is in flower or fruit, from early July through August.

  Conservation / Management

Without knowing exactly where, or even if, L. convallarioides currently occurs in Minnesota, it is difficult to suggest management guidelines. However, assuming L. convallarioides will be rediscovered in the state, and assuming it will be found in a stable, conifer-dominated forest (either an upland forest or possibly a swamp forest), it becomes possible to make some general recommendations. It is safe to say that habitat conditions will need to be maintained. This will likely involve an assessment of the hydrological situation to assure that activities do not alter water movement through the habitat. The integrity of the tree canopy will need to be maintained, and disturbance to the ground layer avoided.

  Conservation Efforts in Minnesota

As no wild populations of L. convallarioides have been rediscovered in Minnesota, no conservation efforts have been directed towards this species.

  References and Additional Information

Catling, P. M. 1976. On the geographical distribution, ecology and distinctive features of Listera x veltmanii Case. Rhodora 78:261-69.

Magrath, L. K., and R. A. Coleman. 2002. Listera. Pages 586-592 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 26. Oxford University Press, New York, New York.

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