Rare Species Guide

  Basis for Listing

Saxifraga cernua (nodding saxifrage) is an arctic-alpine species with a wide distribution across northern Canada and Alaska and scattered populations in the Rocky Mountains. There are also a handful of relict populations in the Black Hills of South Dakota, Gaspe Peninsula in Quebec, Mt. Washington in New Hampshire, and the Border Lakes region of Minnesota in Cook County. The population in Minnesota consists of a single colony with about 20 individuals. It was discovered in 1930 and revisited as recently as 2009. During this period, the population has apparently remained stable at this low number. It is possible that undiscovered populations exist elsewhere in the area, but intensive searches by experienced botanists have failed to locate any. For these reasons, S. cernua was listed as an endangered species in Minnesota in 1984.

  Description

Saxifraga cernua is a distinctive plant easily identified by the reddish bulblets in the leaf axils and at the base of the stem. However, it is a small plant that might be overlooked by anyone not familiar with it, especially if it is not in flower. The stems are generally branchless, reddish in color, and reach a height of 10—20 cm (4-8 in.). They arise each year from a perennial bulb or short rhizome in the ground. There is typically one white flower at the top of the stem; it will have 5 petals, 5-12 mm (0.2-0.5 in.) long. The fruit is a capsule with numerous seeds. The stem is heavily glandular and has several very small leaves spaced alternately along the stem, many with small reddish bulblets in their axils. The leaves at the base of the stems are somewhat larger but seldom more than 2 cm (0.8 in.) long. They are reniform (kidney shaped) and cordate at the base. The margin has 5--7 pointed lobes. They are reported to be somewhat ephemeral and may not be present in late season (Brouillet and Elvander 2009).

  Habitat

The Minnesota population of S. cernua occurs in the cracks, seams, small shelves, and fine crumbly talus of a single north-facing diabase cliff. This habitat type, like that of several other arctic disjuncts, exists in the Rove Formation of the eastern Border Lakes region. This formation is characterized by a series of steep north-facing cliffs separated by deep elongated lakes. The unique geological and glacial history that produced these features is not found elsewhere in the state.

  Biology / Life History

Saxifraga cernua is a perennial but short-lived herbaceous plant. This species may be androdioecious (having staminate and perfect flowers on separate plants), hermaphroditic, or completely sterile (Molau and Prentice 1992). Sexual reproduction is accomplished by insect pollination, primarily by cross pollination but sometimes by selfing. Sterile plants (plants that are not successfully pollinated) reproduce via bulblets that can be produced in abundance. They fall off the parent plant and develop into new plants the following spring (Holm 1925). The bulblets are the primary means of vegetative reproduction. Seed production is generally low in number and of questionable viability (Molau and Prentice 1992). Dispersal mechanisms of seeds and bulblets are undocumented but likely rely on gravity and possibly the activities of small foraging animals. Because reproduction is primarily non-sexual through the production of vegetative propagules (bulblets), S. cernua is often considered a clonal plant (Kapralov 2004). As such, it is probably not greatly affected by failure of pollination/pollinators during any given year.

When observed on 13 June 1999, plants were in full bloom. However, S. cernua is easy to identify when not in flower by the ruby red bulblets in the axils of the leaves.

  Conservation / Management

The Minnesota population of S. cernua is isolated in the remote Boundary Waters Canoe Area Wilderness, and it is not directly threatened by human activities. However, because the entire S. cernua population occupies less than an 80 m² (861 sq. ft.) area, it is vulnerable to singular events that could alter its unstable habitat. From all indications, this small population has subsisted in an extremely harsh and unstable environment for hundreds or perhaps thousands of years, and there is no easy explanation for this remarkable longevity. No active management can be recommended at this time. However, it is recommended that visual monitoring of the population be scheduled no less often than once every ten years.

  Best Time to Search

The best time to search for Saxifraga cernua is when it is in flower, during the month of June.

  Authors/Revisions

Welby R. Smith (MNDNR), 2020

(Note: all content ©MNDNR)

  References and Additional Information

Brouillet, L., and P. E. Elvander. 2009. Saxifraga. Pages 132-146 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 8. Oxford University Press, New York, New York.

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.

Holm, T. 1925. Hibernation and rejuvenation, exemplified by North American herbs. American Midland Naturalist 9(9):439-476.

Kapralov, M. V. 2004. Genotypic variation in populations of the clonal plant Saxifraga cernua in the central and peripheral regions of the species range. Russian Journal of Ecology 35(6):413-416.

Molau, U., and H. C. Prentice. 1992. Reproductive system and population structure in three arctic Saxifraga species. Journal of Ecology 80(1):149-161.