Rare Species Guide

  Synonyms

Rubus setosus

  Basis for Listing

The basis for listing Rubus semisetosus (swamp blackberry) as threatened in 2013 is a well-documented loss of wetland habitat in the counties of central and east-central Minnesota (Wovcha et al. 1995). Because of conversion to agricultural uses and, more recently, to residential and commercial uses, suitable habitats have become exceedingly rare. Perhaps more importantly, surviving habitats have been reduced to small fragments that are isolated from the ecosystem processes, such as fire, that are needed to maintain them. Without fire, they quickly succeed to a closed-canopy forest and lose their characteristic savanna flora. Although information from adjacent states is sketchy, R. semisetosus appears to be rare or infrequent throughout the region (Smith 2008; Widrlechner 1998).

  Description

Rubus semisetosus is a low-growing or midsize shrub. It has biennial stems called “canes”, which grow to 1.3 m (4.3 ft.) in length. The first year canes produce only leaves and grow erect to arching. The second year canes produce leaves and flowers and arch low to the ground. The canes lack hairs but have needle-shaped prickles. The leaves of the first year canes are palmately compound, with 5 or 3 leaflets; the central leaflet is elliptic to elliptic-ovate; the base is rounded to blunt; the apex is acute to acuminate; the lower surface is densely hairy, velvety to the touch. The petioles have slender needle-shaped prickles, and sparse nonglandular hairs. The inflorescence is a leafy raceme, with 7 - 20 white flowers; anthesis is from mid-June to mid-July. The fruit is a black drupe, 8-13 mm (0.3-0.5 in.) across, maturing early August to early September (Smith 2008).

Rubus semisetosus belongs to a group of Rubus called the “bristle-berries”. They differ from other Rubus by having short canes (usually about 1.0-1.5 m [3.3-5 ft.] in length) that arch towards the ground and are usually armed by stiff bristles, rather than by strong prickles. Among the 12 species of bristle-berries found in Minnesota, only two have leaves with velvety undersides: R. semisetosus and R. missouricus (Missouri dewberry) (Smith 2008).

  Habitat

Scattered outlying populations of R. semisetosus have been found as far north as Aitkin and Cook counties, some of them in tamarack swamps. While there is no reason to discount these populations, most occurrences are in savanna remnants farther south, particularly on sand plains in Anoka, Isanti, and Sherburne counties (Anoka Sand Plain Subsection). Savanna populations usually grow in moist sand along the margins of groundwater-fed swales or marshes but also in surface-dry uplands that are just above the water table. These are usually grass- or sedge-dominated habitats, often with scattered brush, such as Corylus americana (American hazel) and Salix humilis (prairie willow) or groves of Populus tremuloides (trembling aspen) or Quercus spp. (oaks.). Because of the low nutrient content of the sandy soil, the vegetation is often rather sparse, which seems to suit R. semisetosus. It clearly does best in direct sunlight or partial shade (Smith 2008).

  Biology / Life History

Rubus is a very large and complex genus of woody and semi-woody shrubs and a few herbaceous species. There are 33 native species and two named hybrids currently known to grow wild in Minnesota. Within these 33 species of Rubus is a smaller group of 12 species called the “bristle-berries”.  Rubus semisetosus is one of the bristle-berries (Smith 2008). 

Rubus semisetosus is a perennial species, though the stems, called “canes”, are biennial, meaning they live for only two years. During the first year, the cane will produce only leaves and is called a "primocane”. The second year, the same cane will produce flowers as well as leaves and is then called a “floricane”. Since R. semisetosus normally produces canes every year, there will be both floricanes and primocanes present on the same plant at any given time. As a result, seeds are normally produced every year. Exceptions occur if canes are damaged by unseasonable frost, drought, browsing by animals, or wildfire (Smith 2008).

The flowers of R. semisetosus are insect-pollinated, and the seeds are dispersed when animals eat the fruit and pass the seeds through their digestive tract. Birds are typical vectors, which means dispersal patterns likely follow the feeding and roosting patterns of frugivorous birds during the month of August.

Reproduction is also accomplished by the growth of rhizomes, which are underground stems that can produce new root crowns at the nodes. Rhizome growth among some species of Rubus can be quite extensive (Smith 2008).

  Conservation / Management

Rubus semisetosus is apparently sensitive to livestock grazing and does not compete well with the weeds that typically follow human disturbance. It is usually found in stable native habitats, with diverse and well-structured plant communities. Maintaining the integrity of these communities and the full complement of native species that constitute the communities is essential for the conservation of R. semisetosus.

Although management tools needed to accomplish this goal will vary from site to site, dormant season prescribed burns should be at the top of the list. Burns must not be too frequent, because R. semisetosus is top-killed by fire and will need time to recover before the next burn. A rotation of no less than four years ought to be adhered to.

Mechanical removal of brush could be useful in situations where fire is not possible, but heavy machinery needs to be avoided because of the damage it can do to soil. Likewise, herbicides must be avoided, even if hand-applied; the risk to non-target species is simply too great.

  Best Time to Search

The best time to search for R. semisetosus is when the inflorescence is fully developed, which normally occurs from late July through August (Smith 2008).

  Authors/Revisions

Welby Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed 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. 352 pp.

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.

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.