Rare Species Guide

  Basis for Listing

Draba norvegica (Norwegian whitlow grass) is a small plant of the far north with amphi-Atlantic distribution; it occurs primarily in northeastern North America and northwestern Europe. In North America, it occurs occasionally on limestone barrens, gravelly shores, bedrock ledges, and cliffs in arctic and subarctic coastal regions of northeastern Canada. There are also a few remarkable populations that are disjunct in the interior of the continent, including one in Minnesota.

The single Minnesota population was discovered in 1937 in an arctic-like habitat on an island in Lake Superior (Butters and Abbe 1953). It was successfully relocated in 1980 and again in 1998. At last count, the plants numbered about 50 and were found on exposed bedrock near the shoreline. This Minnesota population is isolated by several hundred kilometers from the closest populations in Ontario, Canada. In fact, this is the only population known in the United States or in the Great Lakes Basin. How or when it became established cannot be determined, but it is probably the last remnant of a relict population isolated by the changing climate. Draba norvegica was listed as an endangered species in Minnesota in 1984.

  Description

Draba norvegica is a small perennial plant with leaves crowded near the base. It has an unbranched flowering stalk that rises up from 5 to over 10 cm (from 2 to over 4 in.) in height. It is superficially similar to several other members of the mustard family but can be distinguished by the following combination of characters. It is a perennial, the basal leaves are simple (undivided), and the hairs on the leaves are uneven in length and of different types - some hairs are simple, others bifurcate or stellate (star-shaped). The capsules (siliques) are glabrous or nearly so.

  Habitat

Draba norvegica is primarily a plant of arctic and subarctic habitats. It is found in Minnesota only on an island in Lake Superior (North Shore Highlands Subsection) that is composed of Precambrian rock. The island is offshore from the mainland by 7-10 km (4-6 mi.). The interior of the island is forested with Picea spp. (spruce) and Abies balsamea (balsam fir) trees, and the margins consist of exposed bedrock. Draba norvegica occurs on the bedrock shore about 5 m (16 ft.) above the lake level and with a south or southeast exposure. Plants are rooted in narrow crevices in the rock with just enough foothold for them to survive the harsh conditions on the rocky shoreline.

  Biology / Life History

Other than a few generalities that can be gleaned from related species, little is known about the salient life history traits of the Minnesota population of D. norvegica. It is known to be a perennial herb that reproduces regularly by seed, with little or no capacity for clonal reproduction. Specific information that would benefit management decisions includes how recruitment balances mortality, relationship to pollinators, the presence or absence of a seed bank, and how this small remote population will react to ongoing climate change issues.

  Conservation / Management

Draba norvegica is at risk because the only known population in Minnesota consists of a relatively few individuals concentrated in a very small area. This makes it vulnerable to a number of natural and human-caused mishaps that could inadvertently wipe out the population. Fortunately, the site is inaccessible enough that it is rarely visited by people, so human threats are minimal. However, because of its inaccessibility, no attempt has been made to relocate the population since 1998. Although the population probably still survives, it should be verified on the ground more frequently, perhaps every 10 years.

  Best Time to Search

The best time to search for Draba norvegica is when the seed pods are fully developed, mid-June to end of July.  Identification is also possible after the seed pods have released their seeds, because the pods remain on the plant until mid-September.

  Conservation Efforts in Minnesota

The DNR's Minnesota Biological Survey baseline survey has been completed in northeastern Minnesota. Botanists agree that potential habitat for this species has been well-searched, and that substantial new populations are unlikely to be found in Minnesota. The state’s single population of D. norvegica occurs on an island archipelago owned and protected by the Gichi-Onigaming (Grand Portage Band of Lake Superior Chippewa).

  Authors/Revisions

Welby R. Smith (MNDNR), 2020

(Note: all content ©MNDNR)

  References and Additional Information

Butters, F. K., and E. C. Abbe. 1953. A floristic study of Cook County, northeastern Minnesota. Rhodora 55:21-55.

Fernald, M. L. 1934. Draba in temperate northeastern America. Rhodora 36:241-261.

Mulligan, G. A. 1970. Cytotaxonomic studies of Draba glabella and its close allies in Canada and Alaska. Canadian Journal of Botany 48(8):1431-1437.