Thread-leaved sundew (Drosera filiformis) COSEWIC assessment and status report: chapter 4

Global Range 

The global range of thread-leaved sundew extends from the Gulf Coast of Louisiana and Florida, and along the coastal plain of the eastern United States to as far north as extreme southwestern Nova Scotia (Fernald, 1918; Wynne, 1944; Gleason, 1952; Maher et al., 1978; Juniper et al., 1989; Zinck, 1991; Freedman et al., 1992). Populations in the northern part of the range are scattered and disjunct (Figure 2).

Note that some taxonomists consider the populations of the coastal plain of the eastern U.S. and Nova Scotia to be Drosera filiformis, and those of the U.S. Gulf Coast to be Drosera tracyi (Sorrie, 1998).

Canadian Range

In Canada, thread-leaved sundew is only known from five discrete bogs in Shelburne County in extreme southwestern Nova Scotia. The specific sites are known as: (1) Swaines Road (or Barrington) Bog, (2) Port La Tour Bog (this site is probably hydrologically connected to the Swaines Road Bog), (3) West Baccaro Bog; (4) Quinns Meadow; and (5) Villagedale Bog. The first discovery of thread-leaved sundew in Canada was made in the Swaines Road Bog in 1977, and the most recent in the Villagedale Bog in 1999. Extensive surveys have been made of more than 20 other raised bogs in southwestern Nova Scotia having apparently suitable habitat, without finding the rare sundew. Nevertheless, continued surveys of remote bogs may yet discover additional sites.

The disjunct populations of thread-leaved sundewin southwestern Nova Scotia are part of a coastal-plain floristic element involving various species that are rare or unknown elsewhere in Canada (Fernald 1918; Roland and Smith 1969; Wisheu et al. 1994). The populations of these coastal-plain plants are considered relicts of a once more-widely distributed flora that ranged along the exposed continental shelf during periods of lower sea level during the Quaternary. During this time, a land-bridge may have extended from Cape Cod to southwestern Nova Scotia, and as recently as 5,000 years ago there was a substantial remnant archipelago of that landform (Bousfield and Thomas 1975; Roland 1982). Post-glacial rise in sea level isolated the coastal-plain species in Nova Scotia from more broadly distributed communities of this type in the eastern U.S. Many species within the Coastal Plain Flora of Nova Scotia are rare and endangered (Maher et al. 1978; Keddy 1979, 1985; Keddy and Wisheu 1989; Wisheu et al. 1994).

Figure 2. The range of thread-leaved sundew in North America. The distributional information is from Wynne (1944), except for the later-discovered populations in extreme southwestern Nova Scotia.

Figure 2.  The range of thread-leaved sundew in North America. The distributional information is from Wynne (1944), except for the later-discovered populations in extreme southwestern Nova Scotia.

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