. The Canadian field-naturalist. Natural history; Sciences naturelles. 310 The Canadian Field-Naturalist Vol. 120. Figure 4. Patch of pale stems of P. australis subsp. australis on gravel portion of a roadside and extending in a large clone in the adjacent ditch and swamp. Highway 417, Russell Township, May 2003. occurred in all four townships, but the native sub- species was much more localized, with most popula- tions in a single wetland (Figure 2). Invasion Pathway As seen in the distribution maps ( Figure 3) there is a strong association of the introduced subspecies with roads (Figure
. The Canadian field-naturalist. Natural history; Sciences naturelles. 310 The Canadian Field-Naturalist Vol. 120. Figure 4. Patch of pale stems of P. australis subsp. australis on gravel portion of a roadside and extending in a large clone in the adjacent ditch and swamp. Highway 417, Russell Township, May 2003. occurred in all four townships, but the native sub- species was much more localized, with most popula- tions in a single wetland (Figure 2). Invasion Pathway As seen in the distribution maps ( Figure 3) there is a strong association of the introduced subspecies with roads (Figure 4). This is confirmed in the histogram (Figure 5) where the vast majority of the populations of the introduced subspecies are within 100 m of a road. In fact 52% were in the roadside gravel (Figure 4) and 84% were within 3 m of the boundary between vege- tation and gravel shoulder. Populations of the native subspecies occurred at greater distances from a road (Figure 5) with 36% on the shoulder and 60% within 3 m. Although occurrence of the native subspecies on roadsides was much less, it is clearly spreading from natural habitats to roadsides. Since both subspecies may come into close contact on roadsides, there is an opportunity for the subspecies to hybridize. The intro- duced subspecies was most frequent in the eastern townships that have the most roads (Figure 3). The native subspecies was most frequent in the far western township which has the least extensive road network and the most extensive natural wetlands. Major concentrations of the introduced subspecies occurred along Highway 417 (upper right in Figure 3), the busiest and oldest major highway in the region, and the largest patches in Russell township occurred along this road, suggesting that this is one of the places where it first entered the region (Figures 3 and 6). The asso- ciation of the introduced subspecies with roads sug- gested spread by dispersal of rhizomes by road vehi- cles rather than wind-blown see
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