Basis for Listing

The true status of Rubus missouricus (Missouri bristle-berry) in Minnesota has only recently gained some clarity. Previous reports of it occurring in Minnesota were based on fragmentary herbarium specimens that, though very close, do not conclusively match this species. It was not until 2003 that an extant population was found and a careful study could be made. We can now say, with reasonable certainty, that this species is extant in Minnesota; yet it is very rare. During a 10-year statewide survey of Rubus species and habitats, several hundred Rubus populations, representing 33 different species, were located, but only one population of R. missouricus was discovered. The population appears viable but is in a small isolated remnant habitat on the Anoka Sandplain, just north of the Twin Cities (Smith 2008). For these reasons, in 2013 Rubus missouricus was designated an endangered species.

  Description

Rubus missouricus is a midsize shrub. It has biennial stems called “canes”, which grow to 1.5 m (5 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, which are often strong enough to tear skin. The leaves of the first year canes are palmately compound, with 5 leaflets; the central leaflet is elliptic to obovate-elliptic; the base is tapered to rounded; the apex is acuminate; the lower surface is densely hairy, velvety to the touch. The petioles have hooked prickles and sparse nonglandular hairs. The inflorescence varies from a large compound corymb to a reduced simple corymb or raceme, with 7-20 white flowers; anthesis is from mid-June to early July. The fruit is a black drupe, 12-17 mm (0.04-0.06 in.) across, maturing early to late August (Smith 2008).

Rubus missouricus belongs to a group of Rubus called the “bristle-berries”. There are 12 species of bristle-berries in Minnesota. They differ from other Rubus by having short canes (usually about 1 to 1.5 meters (3-5 ft.) in length), which arch towards the ground and are usually armed by stiff bristles, rather than by strong prickles.

Compared to other Minnesota bristle-berries species, R. missouricus is particularly large and robust, with large sharp prickles that are often strong enough to tear skin. The central leaflet of a primocane leaf is often narrowly obovate, which is an unusual shape for a bristle-berry. Also, the undersides of the leaflets are velvety to the touch. The only other bristle-berry with velvety leaves is R. semisetosus (swamp blackberry), which differs by having glandular inflorescences (Smith 2008).

  Habitat

The habitat of the only known occurrence of R. missouricus in Minnesota is a groundwater-sustained sedge meadow on moist sand in nearly full sunlight. It is growing intermixed with other bristle-berries such as R. stipulatus, R. vermontanus (Vermont bristle-berry), and R. fulleri as well as scattered Salix spp. (willow shrubs), Spiraea tomentosa (hardhack), and Betula pumila (bog birch) (Smith 2008).

In Iowa and Missouri, R. missouricus is considered an indicator of upland prairie and savanna habitats, not wetlands. In Iowa, it has even been found in dry hillside prairies, in well-drained sandy or gravelly soil (Widrlechner 1998).

  Biology / Life History

Rubus is a very large and complex genus of woody and semi woody shrubs and a few herbaceous species. Species number perhaps 750 worldwide. There are about 200 to 240 species in the United States, mostly in the eastern half. There are 33 native species and two named hybrids currently known in Minnesota. Within these 33 species of Rubus is a smaller group of 12 species called the “bristle-berries”. R. missouricus is one of these (Smith 2008).

The stems of R. missouricus 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. missouricus normally produces canes every year, there will be both floricanes and primocanes present on the same plant. 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. missouricus are insect-pollinated, and the seeds are dispersed when animals eat the fruit and pass the seeds through their digestive tract. Reproduction is also accomplished by the growth of rhizomes, which are underground stems that can produce new root crowns at the nodes (Smith 2008).

  Conservation / Management

The only known population of R. missouricus in Minnesota occurs in a wetland habitat that is known to be very sensitive to changes in groundwater levels. A lowering or an elevating of groundwater levels at this site would invite a whole suite of non-native invasive species to become established. Of all the invasive species, reed canary grass (Phalaris arundinacea) is perhaps the most serious threat. Invasion would most likely occur where surface water enters the site – these areas need to be watched closely. 

Encroaching woody vegetation, especially Populus tremuloides (trembling aspen), will likely be an ongoing concern. Control methods include cutting, herbicides, and prescribed fire. Herbicides must be used with greatest caution, if at all.

The canes of R. missouricus are also vulnerable to fire. Even though the underground parts of most plants can survive fire, the canes will be consumed. New canes will be produced by surviving plants, but the ability to produce seeds will be lost for the year following fire. Fire will also stress the roots and underground rhizomes, forcing them to expend stored energy to replace above-ground growth. For this reason, fires need to be spaced several years apart.

  Best Time to Search

The best time to search for R. missouricus 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. 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.