Rubus chamaemorus L.
Basis for Listing
Rubus chamaemorus (cloudberry) 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 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 (Border Lakes Subsection). Since that time, only a very few additional colonies have been located (Northern Superior Uplands Section) despite targeted surveys. 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 subterranean network of rhizomes. There are 1-3 leaves per stem, which are suborbicular in outline 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 of R. chamaemorus are more rounded. The white flowers are unisexual, solitary, and terminal, developing into yellowish, deep amber, or reddish fruits (Smith 2008).
In Minnesota, R. chamaemorus has been found in sphagnum bogs dominated by Picea mariana (black spruce) or mixed swamp forests of P. mariana, Alnus incana ssp. rugosa (speckled alder), Betula pumila (bog birch), and sometimes Thuja occidentalis (northern white cedar). It seems to prefer partial shade in thinly forested habitats or full sunlight in forest openings. In more northern parts of its range, it is known to occur in open, non-forested habitats, but in Minnesota it has never been found far from trees, though the trees may be widely spaced and stunted in size.
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 sensitive, non-target species in mind. This may include R. chamaemorus and possibly Nymphaea leibergii (small white waterlily), another rare species in Minnesota (Manguin et al. 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.
Best Time to Search
Although Rubus chamaemorus can be identified at any time during the growing season, the best time to search is from June through August when either flowers or fruits may be present.
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 are subjected to timber management and will require extra consideration to protect this rare plant.
Welby R. Smith (MNDNR), 2021
(Note: all content ©MNDNR)
References and Additional Information
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 L.) in different habitats. Aquilo Series Botanica 13:1-9.
Manguin, S., R. White, B. Blossey, and S. Hight. 1993. Genetics, taxonomy, and ecology of certain species of Galerucella (Coleoptera; Chrysomelidae). Annals of the Entomological Society of America 86(4):397-410.
Rosendahl, C. O. 1955. Trees and shrubs of the Upper Midwest. University of Minnesota Press, Minneapolis. 411 pp.
Smith, W. R. 2008. Trees and shrubs of Minnesota. University of Minnesota Press, Minneapolis. 703 pp.
United States 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, Superior National Forest, Duluth, Minnesota.