Rare Species Guide

  Basis for Listing

Rubus stipulatus (a species of bristle-berry) appears to be one of the rarer species of bristle-berry in Minnesota. It is rare not only in Minnesota but throughout its range, which encompasses only small parts of Minnesota, Wisconsin, and formerly Iowa (Smith 2008; Widrlechner 1998; Davis et al. 1968). Prior to settlement (ca 1850), the core Minnesota range of R. stipulatus was occupied by an expansive oak savanna ecosystem on the Anoka Sand Plain. Within that ecosystem, R. stipulatus occurred at the margins of shallow wetlands. Since the time of settlement, the original savanna ecosystem has been largely supplanted by agricultural fields (Minnesota’s Remaining Native Prairie) and, more recently, by suburban developments Wovcha et al. 1995). Wetlands have survived only to the extent they could not be drained or filled and were able to resist invasion of non-native species, particularly Phalaris arundinacea (reed canary grass [Smith 2008; Wovcha et al. 1995]). The situation has reached the point where only a few small and isolated fragments of habitat still support R. stipulatus; hence it was listed as an endangered species in 2013.

  Description

Rubus stipulatus is a low-growing or midsize shrub. It has biennial stems, called “canes”, which grow to 1.5 meters (4.9 ft.) in length. The canes arch low to the ground or are nearly prostrate; however, they rarely, if ever, tip-root, which is a common character of similar species. The canes lack hairs or glands but have needle-shaped prickles. The leaves of the first-year canes are palmately compound, with 5 or occasionally 3 leaflets; the central leaflet is elliptic in outline; the base is rounded or blunt; the apex is short acuminate; the lower surface usually has at least some hairs on the main veins but is smooth to the touch. The petioles have a few slender and weak prickles; the stipules are lanceolate, conspicuously large, 2.0-3.5 cm (0.8-1.4 in.) long, and often notched on the margin. The inflorescence is a raceme or an open corymb, with 5-19 white flowers, has short and dense non-glandular hairs, and sparser longer and gland-tipped hairs; anthesis is from mid-June to early July. The fruit is a black drupe, 8-14 mm (0.3-0.6 in.) across, maturing from early August to late August (Smith 2008). In nearly all cases, a reliable identification requires an intact first-year stem (primocane) with fully developed leaves, and intact second-year stem (floricane) with fully developed inflorescences. Correct identification can be difficult and may require confirmation from a specialist.

  Habitat

The primary habitat of?R. stipulatus?in Minnesota occurs on the?Anoka Sand Plain. At the time of settlement (ca 1850), this was a nearly level sandplain, with scattered?Quercus macrocarpa?(bur oak) and?Q. ellipsoidalis?(northern pin oak) and perhaps groves of?Populus tremuloides?(quaking aspen) within a matrix of prairie and shallow groundwater-sustained wetlands. Rubus stipulatus is usually found in association with these wetlands. The wetlands are typically open (non-forested), sunny habitats dominated by fine-leaved sedges and rushes. The rooting zone is usually moist to wet, with fine-grained sand in the top 30 cm(12 in.) of soil and a significant component of sedge-derived organic material. Conditions are typically weakly acidic and nutrient poor. Rubus stipulatus is usually found towards the margins of the wetlands where conditions may be dry at the surface during drought years or may support a small amount of standing water at times during a normal year. 

Occurrences of R. stipulatus?outside of the Anoka Sand Plain are few in number and less well-studied. However, they appear to have many similarities with Sand Plain occurrences. They are closely associated with shallow groundwater-influenced wetlands within a forested matrix. The wetland portion of the habitat is typically dominated by sedges and grasses, with little or no presence of non-native invasive species. The forest composition tends more towards Pinus resinosa (red pine) and Larix laricina (tamarack) rather than oak and aspen. Soils are typically weakly acidic sand with a large component of organic material.  

  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”; R. stipulatus is one of these (Smith 2008). 

Rubus stipulatus is a perennial species, though the stems, called “canes”, are biennial, meaning each 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”. The cane will die at the end of the second year. Since R. stipulatus normally produces some 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. stipulatus 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.  

It is believed that asexual reproduction occurs through the underground growth of rhizomes, or possibly from suckering of roots. When this happens, a new root crown is formed some short distance from the mother plant and may develop into an autonomous individual. However, this form of reproduction has not been positively demonstrated in R. stipulatus.

  Conservation / Management

Rubus stipulatus is 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. stipulatus.

Management tools needed to accomplish this goal will vary from site to site, but dormant season prescribed burns should be at the top of the list. Burns must not be too frequent, because R. stipulatus is top-killed by fire and will need time to recover before the next burn. A rotation of no less than four years must 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. Since the habitats are wetlands, it is essential to maintain natural hydrologic conditions. Ditches, drain tiles, impoundments, storm water ponds, etc. are all deleterious to the habitat.

Because of the small and fragmented nature of the habitats, invasive species, especially Phalaris arundinacea, will be an ongoing concern. If the extent of an infestation is limited, then control methods should favor hand removal. Chemical control needs to be avoided, if at all possible.

  Best Time to Search

The best time to search for Rubus stipulatus is when the inflorescence is fully developed, which normally occurs during the month of August (Smith 2008).

  Authors/Revisions

Welby R. Smith (MNDNR), 2018, 2025

(Note: all content ©MNDNR)

  References and Additional Information

Davis, H. A., A. M. Fuller, and T. Davis. 1968. Contributions toward the revision of the Eubati of eastern North America. II. Setosi. Castanea 33(1):50-76.

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.