Drosera anglica Huds.
Click to enlarge
Basis for Listing
Drosera anglica was essentially unknown in Minnesota until 1978 when a particular class of peatland habitat was explored by botanists for the first time (Wheeler and Glaser 1979). These were the large patterned fens of northern Minnesota. The process of identifying and searching these peatland habitats has continued to this day, although most of the ground has now been covered. The results reveal D. anglica to be a rare but integral member of a unique flora inhabiting very sensitive wetlands. Because the hydrologic regime that is necessary to sustain these wetlands can cover vast areas, and a disruption anywhere in the area could have unintended consequences to the unique community of plants existing at the core, there is a need for a heightened level of protection. Drosera anglica was originally listed as a threatened species in Minnesota in 1984, but a better understanding of its distribution and the protection of much its habitat resulted in its reclassification as a special concern species in 1996.
Drosera anglica is a small plant that is inconspicuous except for the rosette of basal leaves that are covered with mucilage-tipped tentacle-hairs that are adapted to trap insects. The leaf petiole is distinct from the blade and 3-7 cm (1.2-2.8 in.) long. The blade of the leaf is narrowly obovate to elongate-spatulate in shape, 1.5-3.5 cm (0.6-1.4 in.) long, and 3-4 mm (0.12-0.16 in.) wide. The stipule is about 5 mm (0.20 in.) long and attached (adnate) to the petiole. The flower stalk (scape) is 6-25 cm (2.4-9.8 in.) high and has 1-9 small white flowers. The seeds are black, spindle-shaped (fusiform), and 1-1.5 mm (0.04-0.06 in.) long. Drosera anglica is most likely to be confused with a common sundew, D. intermedia (spatulate-leaved sundew), but the leaves are larger and the stipules are attached (adnate) to the petioles for about 5 mm (0.20 in.) rather than free from the petioles. Also, the seeds are spindle-shaped (fusiform) rather than oblong, and black rather than reddish-brown (Wynne 1944).
In Minnesota, D. anglica occurs exclusively in fens of open rich peatlands, primarily in water tracks in the interiors of large peatlands. The habitat is dominated by fine-leaved sedges such as Carex lasiocarpa ssp. americana (fen wiregrass sedge) with scattered low shrubs and stunted Larix laricina (tamarack) or Picea mariana (black spruce). These are very wet sites with subtle mossy hummocks and open peat-bottomed pools. The surface water is weakly acidic with a pH ranging from 5.6-7. The groundwater is near the surface and stable throughout the year (Minnesota Department of Natural Resources 2003).
Biology / Life History
The most unusual aspect of the biology of D. anglica is its ability to actively capture and digest small insects. This is presumably a way to obtain fixed nitrogen, which is a limiting nutrient in peatland habitats. The flowers are evolved for insect pollination, although self-pollination does occur. The seeds have no specialized dispersal mechanism and probably move about on subtle currents of the surface water. There is strong evidence that D. anglica, a tetraploid, arose through hybridization between D. linearis (linear-leaved sundew) and D. rotundifolia (round-leaved sundew), both diploids (Wood 1955). The modern day amphiploid is fully fertile and reproductively isolated from its putative parents. Sterile hybrids between the two parent species can apparently be found on the modern landscape, and a sterile hybrid between D. anglica and D. linearis has also been reported (Schnell 1995). From the perspective of conservation, the significance of a hybrid origin is not great. A relatively large number of extant plant species are believed to have arisen in this manner.
Conservation / Management
The habitat type occupied by D. anglica is dependent on very specific patterns of surface and subsurface water flow that are easily disrupted. Even the slightest disruption or alteration to the broad-scale hydrology that feeds a fen can have severe and irreversible effects on the habitat and the flora. Numerous examples of this have been seen, especially related to peat mining, rice cultivation, and road building. For this reason, any analysis of the impacts of land alteration projects within the watershed of a fen must involve a sophisticated understanding of the regional hydrology. Several D. anglica populations are located in very small spring fens, which makes them especially vulnerable to activities in adjacent upland areas.
Conservation Efforts in Minnesota
Most of the areas harboring D. anglica are large, remote, water-logged peatlands that have traditionally been considered worthless wastelands with no potential for economic development. For this reason, they have generally remained in public ownership with little pressure from extractive or consumptive users of natural resources. That changed in the 1970s when high energy prices triggered a search for new energy sources. Energy companies soon realized that peat could be turned into natural gas and subsequently proposed to mine the peat from Minnesota's largest peatland. Although it was eventually deemed uneconomical, the prospect of Minnesota's peatlands being drained and mined alarmed land managers and conservationists. As a result, the core areas of most large peatlands in the state have been designated as Scientific and Natural Areas, which should provide a high level of protection.
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.
Schnell, D. E. 1995. A natural hybrid of Drosera anglica Huds. and Drosera linearis Goldie in Michigan. Rhodora 97:164-170.
Wheeler, G. A., and P. H. Glaser. 1979. Notable vascular plants of the Red Lake Peatland, northern Minnesota. The Michigan Botanist 18:137-142.
Wood, C. E. 1955. Evidence for the hybrid origin of Drosera anglica. Rhodora 57:105-130.
Wynne, F. E. 1944. Drosera in eastern North America. Bulletin of the Torrey Botanical Club 71(2):166-174.