. The Canadian field-naturalist. 1990 HOULE AND HABER: STATUS OF GULF OF ST. LAWRENCE ASTER 457. Figure 3. Shoreline habitat of Aster laurentianus at He de la Grande Entree, Magdalen Islands. Arrow points to the aster. F2 hybrids. Enzymatic studies (Houle 1988) and the higher degree of crossabihty between A. laurentianus and A. brachyactis indicate a closer genetic affinity between these two species. Reciprocal crosses, however, have been unsuccess- ful, suggesting sporophytic cross-incompatibility. In nature the three species are reproductively isolated because they are predominently self- po
. The Canadian field-naturalist. 1990 HOULE AND HABER: STATUS OF GULF OF ST. LAWRENCE ASTER 457. Figure 3. Shoreline habitat of Aster laurentianus at He de la Grande Entree, Magdalen Islands. Arrow points to the aster. F2 hybrids. Enzymatic studies (Houle 1988) and the higher degree of crossabihty between A. laurentianus and A. brachyactis indicate a closer genetic affinity between these two species. Reciprocal crosses, however, have been unsuccess- ful, suggesting sporophytic cross-incompatibility. In nature the three species are reproductively isolated because they are predominently self- pollinating and because of the geographical isolation of A. laurentianus. Population size and trends Thirteen localities have been confirmed by the senior author. A search for the aster in suitable habitats of Kouchibougouac National Park, where it has been reported to occur, was unsuccessful. Table 1 lists the 13 verified localities and the number of plants individually counted or estimated to occur at the sites. Fewer than 1000 plants have been counted in total at 13 of the extant populations known from Prince Edward Island (23 plants), New Brunswick (200) and Quebec (Magdalen Islands, 661). A search for the aster at Grand Tracacie, PEI, a verified historic locality, was unsuccessful. Limiting factors The rarity of A. laurentianus in suitable maritime habitats probably reflects its relatively low survival rate in nature in spite of its relatively high germination capabihty, at least as demon- strated under controlled conditions. No clear evidence of threats to the survival of ^4. laurentianus has been noted. Plants were not found at Brackley Point in Prince Edward Island National Park, the type locality for the species, but another population was located nearby at Brackley Beach. This can be interpreted as representing a natural displacement of an annual species. However, critically low population numbers and high human pressure do exist at the Park. Future developments in the
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