Rubus multifer Bailey
Basis for Listing
Rubus multifer (Kinnickinnick dewberry) is found in high-quality savanna remnants on the Anoka Sandplain Subsection and on a few bedrock exposures in prairie habitats elsewhere (Eastern Broadleaf Forest Province). In the past, these habitats were probably common, and R. multifer was perhaps correspondingly common as well. However, the situation has now changed dramatically. Savanna habitats, even small remnants, have become exceedingly rare (Minnesota's Remaining Native Prairie) (Smith 2008). On the basis of the small number of known populations and the limited amount of remaining habitat for the species in the state, R. multifer was listed as a special concern species in 2013.
Rubus multifer is a low shrub with biennial canes commonly over 1.5 m (5 ft.) long and sometimes over 2.2 m (7 ft.), but they are weak and usually trail along the ground their entire length; and, since the inflorescence and leaves are relatively small, the entire plant is easily hidden in tall grass. The canes will frequently root at the tip, in the typical fashion of dewberries, but not until sometime in August, when they have reached their full length. The prickles tend to be short and rather weak and many do not last into the second year. Leaves on the first-year stems almost always have 5 leaflets, which are relatively small and roundish, with an abruptly short-pointed tip, and the lower surface is sparsely to moderately hairy. The inflorescence is ascendate, with 1-6 white flowers, and the fruits are globose to short-conical and 12-16 mm (0.5-0.6 in.) across (Widrlechner 1998).
The most vigorous populations seem to be found in isolated remnants of the indigenous oak savanna or oak-aspen woodlands. These habitats typically have scattered groves of Quercus macrocarpa (bur oak), Q. ellipsoidalis (northern pin oak), or Populus tremuloides (trembling aspen), with intervening prairie-like habitats and shallow wetlands. In this situation, R. multifer is usually rooted in dry or slightly moist sand or occasionally in crevices of granite outcrops (Stearns and Benton counties) or in thin soil over sandstone bedrock (Washington County). It is not found under direct tree cover, rather, it prefers full sunlight among grasses or partial shade among shrubs (Smith 2008).
Biology / Life History
Rubus multifer is a woody shrub, with long stems called “canes”. The canes can reach 2.5 m (8 ft.) in length, but they are slender and relatively weak and cannot support their entire length. So instead of growing upright, the canes trail along the ground for at least a portion of their length. This is also a species that prefers fire-maintained habitats. Although the canes are consumed by a typical ground fire, replacement stems sprout vigorously from the durable root system. The canes are biennial, which means they live for only two years. The first year, the cane will produce only leaves and is called a “primocane”. The second year, the same cane will produce flowers and is then called a “floricane”. Since healthy plants are continuously producing canes, there will normally be both types of canes on each plant at any given time. The stems have another interesting feature - they root at their tips in the late summer of their first year, thereby establishing a new root crown, independent of the parent root system. This process often leads to the formation of a sizeable colony.
Reproduction is also accomplished by the production and dissemination of seeds. The vector for seed dispersal is typically a bird or mammal that eats the fleshy fruit and expels the seeds in its droppings. Pollination is accomplished by a variety of non-specialized flying insects, especially bees.
Conservation / Management
Spring wildfires ignited by lightning strikes were common in these habitats until about the turn of the twentieth century. By that time, the continuous savanna ecosystem had been fragmented by farm fields and roads and, more recently, by residential developments. Fire, which is now understood to be essential to the health of the savannas, is sometimes used as a management tool to restore and enhance native savanna vegetation, at least in those isolated patches that have been saved for conservation purposes. Rubus multifer, as well as the other dewberries and blackberries that are native to savannas, responds very well to periodic fire, especially dormant-season fire at intervals of 4-8 years. Under these conditions, R. multifer can become very competitive with grasses and broad-leaved herbaceous plants, even developing large luxuriant clones 3-6 m (10-20 ft.) across.
Best Time to Search
As with all members of the genus Rubus, the best time to search for R. multifer is when plants are in fruit, rather than in flower, mid-July to mid-August is best.
Welby Smith (MNDNR), 2018
(Note: all content ©MNDNR)
References and Additional Information
Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the eastern broadleaf forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 394 pp.
Minnesota Department of Natural Resources. 2006. Tomorrow's habitat for the wild and rare: An action plan for Minnesota wildlife, comprehensive wildlife conservation strategy. Division of Ecological Services, Minnesota Department of Natural Resources. 297 pp. + appendices.
NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia.
Smith, W. R. 2008. Trees and shrubs of Minnesota. University of Minnesota Press, Minneapolis. 703 pp.
Widrlechner, M. P. 1998. The genus Rubus L. in Iowa. Castanea 63(4):415-465.
Wovcha, D. S., B. C. Delaney, and G. E. Nordquist. 1995. Minnesota's St. Croix River Valley and Anoka Sandplain:a guide to native habitats. University of Minnesota Press, Minneapolis. 248 pp.