Blunt-lobed woodsia (Woodsia obtusa) COSEWIC assessment and status report: chapter 4

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Distribution

Global range

Blunt-lobed woodsia is widespread in the eastern United States, occurring in all states east of the 100th parallel (except North Dakota and South Dakota), reaching north to south-eastern Canada (Ontario and Quebec) and extending south to south-central Texas and northern Florida (Figure 2). It is generally not found on the Atlantic coastal plain (Brown 1964). It is a common species in the northeastern United States.

Figure 2. Distribution map of blunt-lobed woodsia in North America(modified from Flora of North America Editorial Committee (1993)).

Canadian range

The extreme northern limit of this species’ range extends into southern Ontario and Quebec; in fact, no Canadian populations are situated more than 100 km from the US border. The first Canadian report of blunt-lobed woodsia was from Missisquoi County in southern Quebec in 1936 by Belval and Raymond (Cinq-Mars 1969). The Canadian extent of occurrence for this species is estimated to be approximately 14 000 km². This is based on an area, triangular in shape, ranging from Frontenac Park, ON, north to Gatineau Park, QC, and east to the clumped Quebec populations at Saint-Armand/Frelighsburg. This amounts to less than 1% of the species’ global range. The species’ area of occupancy in the Canadian range is estimated to be less than 1 km². Of the nine known populations, four occur in Ontario and five in Quebec (Figure 3).

Figure 3. Location of the nine known Canadian populations of blunt-lobed woodsia.

Province of Ontario

All four populations are found on the Frontenac axis, a southern extension of the Precambrian shield extending from the Gananoque and Brockville area along the St. Lawrence River, north to the Westport area. Three populations occur within a few kilometres of each other along the north shores of Big Rideau Lake and Sand Lake near Westport. The other is located in Frontenac Park, approximately 20 km southwest from the others.

Province of Quebec

The five Quebec populations, one of which is likely now extirpated, are found in two distinct regions, separated by several hundred kilometres. Three of these populations are found on dolomite in Missisquoi County; the other two occur on marble bedrock slopes along the Eardley Escarpment in Gatineau Park.