Rare Species Guide

  Synonyms

Oxytropis viscida, Oxytropis ixodes

  Basis for Listing

In Minnesota, Oxytropis borealis var. viscida (sticky locoweed) is restricted to a single cliff in Cook County (Border Lakes Subsection). It is disjunct from arctic and alpine habitats far to the north and west. The population was originally discovered in 1938 and still persists. Such a small isolated population is vulnerable to a variety of stochastic processes attributable to natural events and human-caused impacts. For this reason, Oxytropis borealis var. viscida was listed as an endangered species in Minnesota in 1996.

  Description

This small stemless legume has a thick taproot and numerous basal divided leaves, each with 15-25 pairs of linear leaflets. Leaves are opposite, scattered, and variously pubescent. Flowers of Minnesota plants are generally purple, but elsewhere they can vary from whitish to blue. Oxytropis borealis var. viscida is unique within its genus by virtue of its viscid (sticky with glandular warts) bracts and inflorescence. Its bracts are glabrous or nearly glabrous. There is no other species in the forested region of Minnesota that has the general appearance of this plant (Gleason and Cronquist 1991).

The Minnesota plants differ morphologically from the original description of this species, and they are geographically separated by at least 950 km (590 mi.) from the main range of the species. For these reasons, Butters and Abbe (1943) initially thought this was a new species and named it O. ixodes. More recently, botanists have determined that the Minnesota plants are not a distinct species after all. They are part of the O. borealis var. viscida complex, which is quite variable and widespread.

  Habitat

The Minnesota O. borealis var. viscida population occurs on a single north to northwest facing cliff face and at the top of the corresponding talus slope. Plants occur in both sunny and partially shaded conditions where there is little competition from typical forest species; this is similar to the habitat occupied by the species in the Rocky Mountains. This population is apparently a relict of a wider preglacial distribution.

  Biology / Life History

Oxytropis borealis var. viscida is a relatively long-lived perennial, reported to have a life-span of 20-40 years (Mulder and Harmsen 1995). It is an herbaceous, leguminous herb that produces dry, dehiscent fruits. The flowers appear in late May and June and are pollinated by insects, including moths and butterflies. It does not reproduce vegetatively, relying only on seeds. Typical of legumes, it is able to convert atmospheric nitrogen to a form useful to the plant, which may give it a competitive advantage in the harsh environment in which it lives. Seeds likely do not form a long-term seed bank, though they reportedly benefit from scarification (Kaye et al. 1997).

  Conservation / Management

The Minnesota O. borealis var. viscida population may be affected by natural erosion and dislocation of the unstable cliffs and talus that this species inhabits. This is a natural process that will probably not threaten the population unless the number of individual plants gets too small. However, land alterations to the adjacent cliff-top forest could increase erosion, competition, and the occurrence of non-native species. Such increases could create an unnatural level of instability, further limiting available habitat and undermining the plants themselves. The increasing popularity of rock climbing and off-trail hiking to scenic overlooks at the top of the cliff could also negatively impact this species' habitat. In fact, some plants have already been damaged by this activity. The upper cliff zone and adjacent outcrop/woodland is very vulnerable to trampling, especially in dry periods when the abundant lichens and sparse vegetation are extremely brittle. Nearby trails, including previously closed trails, will need to be monitored and maintained.

  Best Time to Search

The best time to search for Oxytropis borealis var. viscida is when it is in flower, from early June through mid-July, but it can be reliably identified from May to September.

  Conservation Efforts in Minnesota

The development and implementation of a formal monitoring program for O. borealis var. viscida is strongly warranted. A conservation plan should also be developed with the site's landowners to help assure and guide long-term conservation of the site.

  Authors/Revisions

Welby R. Smith (MNDNR), 2021

(Note: all content ©MNDNR)

  References and Additional Information

Butters, F. K., and E. C. Abbe. 1943. A new Oxytrope of the Minnesota-Ontario border. Rhodora 45:1-4.

Gerdes, L. B. 2001. A contribution to the flora of the Rove Slate Bedrock Complex Landtype Association, northern Cook County, Minnesota, U.S.A. Thesis, Michigan Technological University, Houghton. 79 pp.

Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. Second Edition. New York Botanical Garden, Bronx, New York. 910 pp.

Kaye, T. N. 1997. Seed dormancy in high elevation plants: implications for ecology and restoration. Pages 115-120 in T. N. Kaye, A. Liston, R. M. Love, D. L. Luoma, R. J. Meinke, and M. V. Wilson, editors. Conservation and management of native plants and fungi. Native Plant Society of Oregon, Corvallis.

Mulder, C. P. H., and R. Harmsen. 1995. The effect of muskox herbivory on growth and reproduction in an arctic legume. Arctic and Alpine Research 27(1): 44-53.