Rare Species Guide

  Synonyms

Narthecium pusillum

  Basis for Listing

Several small populations of Tofieldia pusilla (small false asphodel) occur on the North Shore of Lake Superior and nearby Isle Royale, but they are isolated from the main range of the species by approximately 650 km (404 mi.). This remarkable pattern of disjunction is seen in several other arctic species and is a result of the local climate-modifying effect of Lake Superior that simulates growing conditions like those in arctic/alpine regions where these plants may be more common. The small population sizes and sensitive habitat requirements make the viability of the Minnesota populations a matter of immediate concern (U.S. Forest Service 1999). Tofieldia pusilla was listed as an endangered species in Minnesota in 1984.

  Description

Tofieldia pusilla is a small inconspicuous plant. Flowering stems (peduncles) are unbranched and leafless and usually stand about 10-15 cm (4-6 in.) tall. The leaves are clustered near the base of the plant and are rather inconspicuous. They are slender (almost grass-like), about 5-8 cm (2-3 in.) long, and grow stiffly upwards. The flowers are white or greenish white and clustered in a group of 3-35 near the top of the peduncle. The individual flowers are very small, usually less than 5 mm (0.2 in.) across. Each flower will have 3 petals, 3 sepals, 3 styles, and 6 stamens. The fruit is a small roundish capsule containing a few dark seeds. Most plants do not flower in any particular year and will be very difficult to find. The above-ground portion will consist of a small cluster of stiff, almost succulent, sword-like leaves. The underground portion is a short rhizome that produces fibrous roots (Packer 2002).

  Habitat

All of the known populations of T. pusilla in Minnesota are found in similar habitats on the shore of Lake Superior (North Shore Highlands Subsection). The habitats are in crevices of the massive outcrops of volcanic bedrock, not the unstable gravel beaches or the boulder-strewn shorelines. Suitable habitat is found intermittently from Two Harbors to Grand Portage, a distance of 200 km (124 mi.) but may total only a few hectares in extent. Tofieldia pusilla occurs in vegetation mats of Trichophorum cespitosum (tufted bulrush), Carex spp. (sedges), and other low-growing species that persist in crevices in the shore outcrops between the lake and the adjacent forest. These vegetation mats typically form in low depressions and at the margins of shore pools where they are continually moist. Such habitats are small and localized, occurring just beyond the wave-washed zone or in protected areas nearer to lake level. Other rare species that may occur in the same habitat include Pinguicula vulgaris (butterwort), Bistorta vivipara (alpine bistort), and Selaginella selaginoides (northern spikemoss).

  Biology / Life History

Tofieldia pusilla is a perennial, growing from a relatively long-lived rhizome. Most plants in a population will not flower in any given year, but those that do send up a single peduncle (flowering stem) in June. Each peduncle will have up to 35 small insect-pollinated flowers that develop in July. Flowers that are successfully pollinated will produce seed capsules in August. The seeds possess no specialized dispersal structures and are likely dispersed short distances by gravity, gusts of wind, and possibly small foraging animals, likely arthropods.

  Conservation / Management

The most serious threats to the extant populations of T. pusilla in Minnesota include vandalism, recreational use of its habitat (trampling), shoreline development, and the expanding gull population. Climate change that can alter the sensitive microclimate along Lake Superior is also a potential threat (U.S. Forest Service 1999). Although the bedrock substrate of these populations is seemingly indestructible, the vegetation mats that support this species are very fragile.

  Best Time to Search

The best time to search for Tofieldia pusilla is during flowering in July or while fruiting in August. This species is quite distinct even when flowers or fruits are not present, but it is very inconspicuous at such times and difficult to find.

  Conservation Efforts in Minnesota

Much of the potential habitat along Lake Superior was inventoried by the DNR Minnesota Biological Survey from 1999-2002. It is possible that a few additional populations occur outside the surveyed areas, such as extreme northeastern Cook County.

  Authors/Revisions

Welby R. Smith (MNDNR), 2020

(Note: all content ©MNDNR)

  References and Additional Information

Packer, J. G. 2002. Tofieldia. Pages 60-61 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 26. Oxford University Press, New York, New York.

U.S. Forest Service. 1999. Population viability assessment in forest plan revision. Statement of purpose and reason. Draft species data records: Tofieldia pusilla. U.S. Forest Service, Region 9, Superior National Forest, Duluth, Minnesota.