Rubus chamaemorus L.
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Basis for Listing
Rubus chamaemorus is an arctic and boreal species that is typical of circumpolar bog habitats in North America, Europe, and Asia. The southern limit of its range in North America is ill defined and is represented by local and discontinuous populations in northern New England and disjunctive sites at Montauk Point, Long Island, and northeastern Minnesota. This species was unknown in Minnesota until 1954 when it was discovered near a research facility on Basswood Lake in the Superior National Forest in Lake County. Since that time, only a very few colonies have been located despite targeted surveys. It is possible that currently unknown populations may yet be discovered. Rubus chamaemorus was listed as a threatened species in Minnesota in 1984.
Although Rubus can be a very confusing genus, R. chamaemorus is quite distinctive and can be readily identified in the field. The plant notably lacks prickles or bristles and reaches a height of only 10-30 cm (4-12 in.). The slender stems are herbaceous, not woody, and arise from a creeping, subterranean network of rhizomes. There are 1-3 leaves per stem, which are suborbicular in outline and simple, with approximately 5 lobes and finely toothed margins. The leaves can be confused with those of Ribes triste (swamp red currant) and possibly R. glandulosum (skunk currant), but the lobes are more rounded. The white flowers are unisexual, solitary and terminal, developing into yellowish, deep amber or reddish fruits.
In Minnesota, R. chamaemorus has been found in sphagnum bogs dominated by Picea mariana (black spruce) or mixed forests of P. mariana, Alnus incana ssp. rugosa (speckled alder), Betula pumila (bog birch), and sometimes Thuja occidentalis (northern white cedar). It is often found on deep sphagnum hummocks associated with Calamagrostis canadensis (bluejoint), Carex trisperma (three-seeded bog sedge), Gaultheria hispidula (creeping snowberry), Rhododendron groenlandica (Labrador tea), and Smilacina trifolia (three-leaved false Solomon's seal).
Biology / Life History
Individual flowers last a very short time, possibly only 2 or 3 days. There is an inherent tendency for the male plants to flower too early to pollinate many female plants, resulting in poor pollination (Lohi 1974). Reproduction by seed does occur and is essential for dispersal, but it is apparently uncommon (fide Korpelainen 1994). The main mode of reproduction is vegetative. This is accomplished by an extensive system of branched rhizomes that grow just beneath the surface of the moss and send up herbaceous aerial stems from the nodes. Each aerial stem produces 1 to 3 leaves and occasionally 1 flower. Studies have shown rhizomes can be up to 10 m (33 ft.) long, and comprise from 92-97% of the biomass of the clone (fide Korpelainen 1994). It has also been shown that the actual number of clones in any population is typically low (fide Korpelainen 1994), and there is evidence that male clones predominate (Agren 1988). It is even possible that a small "population" may consist of a single, diffuse clone, which would be all male or all female even if the clone consisted of hundreds of stems. This could be especially significant in Minnesota, where populations are particularly small and isolated, and where conservation is a concern.
Conservation / Management
In Scandinavia, the Galerucella beetles that are used as a biological control against Lythrum salicaria (purple loosestrife) are known to feed on R. chamaemorus, in addition to many species of water lilies. Two species of Galerucella beetles already exist in North America, but the introduction of the European species must be done with the needs of the sensative species in mind. This may include R. chamaemorus and possibly Nymphaea leibergii (small white waterlily), another rare species in Minnesota (Manguin 1993). Rubus chamaemorus sites contain stands of small, but usually merchantable, P. mariana that may be harvested for pulp. Because of the fragile nature of the peat soils, harvesting in the vicinity of known locations of R. chamaemorus should be avoided, even in winter.
Conservation Efforts in Minnesota
All known R. chamaemorus sites occur on publicly owned land, chiefly within the Superior National Forest. Two of these sites are in the Boundary Waters Canoe Area Wilderness, a federally designated wilderness area that is protected from incompatible human activities. The other known sites are on lands that include timber management, and they will require extra consideration to protect this rare plant.
Agren, J. 1988. Sexual differences in biomass and nutrient allocation in the dioecious Rubus chamaemorus. Ecology 69:962-973.
Korpelainen, H. 1994. Sex ratios and resource allocation among sexually reproducing plants of Rubus chamaemorus. Annals of Botany 74:627-632.
Lakela, O. 1954. The occurrence of Rubus chamaemorus in Minnesota. Rhodora 56:272-273.
Lohi, K. 1974. Variation between cloudberries (Rubus chamaemorus) in different habitats. Aquilo Series Botanica 13:1-9.
Manguin, S., F. White, B. Blossey, and S. Hight. 1993. Genetics, taxonomy, and ecology of certain species of Galerucella (Coleptera; Chrysomelidae). Annuals of Entomological Society of America 86(4):397-410.
Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis, Minnesota. 320 pp.
Rosendahl, C. O. 1955. Trees and shrubs of the Upper Midwest. University of Minnesota Press, Minneapolis, Minnesota. 411 pp.
Smith, W. R. 2008. Trees and shrubs of Minnesota. University of Minnesota Press, Minneapolis. 703 pp.
U.S. Forest Service. 2000. Population viability assessment in forest plan revision. Questions for plant population viability assessment panel: Rubus chamaemorus. United States Forest Service, Region 9, Duluth, Minnesota.