Rubus fulleri Bailey
Basis for Listing
Rubus fulleri (a bristle-berry) is a Midwestern plant, with a very limited distribution in Minnesota and adjacent states (Widrlechner 1998; Smith 2008). The habitat of R. fulleri is shallow wetlands on sandplains in central and east-central Minnesota (Eastern Broadleaf Forest Province). This is a very fragile habitat type that is susceptible to being drained, filled, invaded by exotic species, or otherwise destroyed. In fact, after more than 100 years of agricultural and urban development in this area, there are very few examples of this type of habitat surviving in a condition suitable to sustain populations of this species (Minnesota's Remaining Native Prairie, which includes marshes and sloughs). The remaining habitats are small isolated fragments that will need intensive management if they are to sustain viable communities of native plants. Since R. fulleri does not readily colonize new habitats, the prospect of restoring lost habitat is not likely to benefit this species, so saving existing habitat is critical (Smith 2008). For these reasons, R. fulleri was designated a threatened species in 2013.
Rubus fulleri is a low-growing vine-like shrub. It has biennial stems called “canes”, which grow to 1.5 meters (5 ft.) long. The first year canes bear only leaves and grow upwards at an angle or arch towards the ground, often rooting at the tips. The second year canes produce leaves and flowers and lie on the surface of the ground. The canes frequently have dense gland-tipped hairs, at least on the first-year cane; they are also armed with weak aciculate prickles or stiff bristles. The leaves of the first-year canes are palmately compound, with 3 or 5 leaflets; the central leaflet has a rounded base and an acute apex; the lower surface is nearly smooth. The petioles have gland-tipped hairs and weak prickles. The inflorescence is an open corymb, or sometimes a raceme, with 5-20 white flowers; anthesis is from mid-June to mid-July. The fruit is a black drupe, 10-15 mm (0.4-0.6 in.) across, maturing early to late August (Smith 2008).
Rubus fulleri 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 1.0 to 1.5 meters (3-5 ft.) in length), which arch towards the ground and are armed by stiff bristles, rather than by strong prickles.
The first year canes of R. fulleri start erect, but by mid-August they will have reached about 1 m (3 ft.) in length and begun to arch toward the ground. When the tip reaches the ground, it will take root if soil and moisture conditions permit. This may be the only character that separates closely related species, so it is essential to examine several healthy and undamaged canes to establish if the plant is a “tip-rooter”. Also note that the canes have soft gland-tipped hairs intermixed with stiff bristles. The only similar Minnesota species that have glandular canes are R. regionalis (Wisconsin dewberry), R. groutianus, and R. dissensus (Smith 2008).
Rubus fulleri is found almost exclusively on sand plains in the central and east-central counties (Anoka Sandplain Subsection) (Wovcha et al. 1995), typically in habitats called swales or wet meadows. These are shallow wetlands sustained by a high water table and have a ground layer of sedges, broad-leaved herbaceous plants, and often scattered shrubs. Adjacent uplands may also be suitable, if there is direct sunlight and little competition (Smith 2008).
The best examples of these habitats are essentially remnants of the original oak savanna ecosystem that existed in the region before settlement. There is a whole suite of similar “bristle-stemmed” Rubus species that typically occur with R. fulleri in habitats of this type. They include R. stipulates (a bristle-berry), R. uniformis (thornless dewberry), R. semisetosus (swamp blackberry), R. vermontanus (Vermont bristle-berry), and R. dissensus (Smith 2008). They often dominate the low-shrub layer, with large clones integrated into complex and highly structured communities or segregated into zones along moisture and light gradients.
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 200-240 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”, and R. fulleri is one of them.
The stems of R. fulleri 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. fulleri 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.
The flowers of R. fulleri 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. New root crowns can also be produced where the tip of the first year aerial stem (primocane) comes into contact with the ground; a process called “tip-rooting” (Smith 2008).
Conservation / Management
Rubus fulleri is known to be very sensitive to livestock grazing and changes in groundwater levels and does not readily colonize grossly disturbed habitats. The canes of R. fulleri are also vulnerable to fire. Even though the below-ground parts of most plants will survive fire, all the above-ground growth will be consumed, which will eliminate seed production for at least one year. And yet, fire can be a useful method of controlling encroaching woody vegetation in R. fulleri habitat; just always remember that R. fulleri is a woody species.
Because of the small and fragmented nature of the habitats, invasive species, especially reed canary grass (Phalaris arundinacea), will be an ongoing concern. If the extent of an infestation is limited, then control methods should favor hand removal. Chemical control should be avoided if at all possible.
Best Time to Search
The best time to search for R. fulleri is when the inflorescence is fully developed, which normally occurs from late July to late August (Smith 2008).
Welby Smith (MNDNR), 2018
(Note: all content ©MNDNR)