Rare Species Guide

  Basis for Listing

Little is known about Rubus quaesitus (Prince Edward Island blackberry) other than it is apparently rare throughout its range. There are authenticated specimens from only a few locations in New Brunswick, Wisconsin, and Minnesota. It was first discovered in Minnesota by Albert Fuller in 1958 at a Rubus-rich site in Kanabec County. The site was revisited in 2003, but R. quaesitus could not be found. The only other confirmed site was discovered in 1998 in Carlton County (Laurentian Mixed Forest Province). As a measure of its rarity, this was the only discovery of R. quaesitus among 500 or more Rubus populations investigated during a statewide field survey (Smith 2008). Although there are other possible populations being investigated which may turn out to be R. quaesitus, at this time only one is known; hence, R. quaesitus was listed as a special concern species in 2013.

  Description

Rubus quaesitus is a midsize shrub, with biennial stems that range from 0.6 to 1.5 m (2-5 ft.) long, and they tend to arch or lean, but they do not trail along the ground or tip-root; and they have strong and sharp broad-based prickles. Leaves of the first-year stems are palmately compound, with 5 leaflets; the lower surface is glabrous or with a few hairs along mid and lateral veins. The inflorescence is a raceme, with 7-15 white flowers; each flower is 2.5-3.8 cm (1-1.5 in.) across. The fruit is black, globular or short-cylindrical, and 1-2 cm (0.4-0.8 in.) long (Davis et al. 1969).

  Habitat

The only population of R. quaesitus currently known in Minnesota is small but apparently well established in a mature northern mesic mixed forest of Populus tremuloides (trembling aspen) and Betula papyrifera (paper birch). The soil is mesic sandy-loam and sunlight is filtered or patchy for most of the day (Smith 2008).

  Biology / Life History

Very little has been published about the ecology or natural history of R. quaesitus, other than a meager note crediting it with producing unusually large fruit, even in poor blackberry years (Davis et al. 1969). Beyond that, some assumptions can be made based on attributes of similar Rubus species living in the area. For example, R. quaesitus is probably fire-adapted and may require small intermittent canopy gaps for sufficient sunlight. The flowers are likely pollinated by a number of flying insects, and the seeds are likely dispersed by frugivorous birds and a variety of mammals.

As with all the blackberry species, the canes (stems) of R. quaesitus 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 most blackberry plants are continuously producing canes, there will normally be both types of canes on each plant at any given time.

  Conservation / Management

Since so little is known about this species in Minnesota, the first step should be to map and census the population. A more thorough analysis of the habitat where the known population occurs could also reveal much. One step in the process might be to reconstruct the land use history of the site, particularly any history of logging or livestock grazing. This may lead to a plan for active management of the site, such as shrub removal or invasive species control, or it may reveal that protective passive management is the best approach.

  Best Time to Search

The best time to search for R. quaesitus is during the period when fruit are present. The fruit themselves are not needed for identification but a fully developed inflorescence is, which coincides with the presence of fruit. The month of August is the best time to search.

  Authors/Revisions

Welby Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Davis, H. A., A. M. Fuller, and T. Davis. 1969. Contributions towards the revision of the Eubati of eastern North America. IV. Castanea 34(2):157-179.

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.

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.