. The Canadian field-naturalist. Natural history. 1995 Catling and Brownell: Alvars of the Great Lakes Region 157 Manitoulin are part of a large group of plants includ- ing western, cordilleran and boreal disjuncts, which in the Great Lakes region are largely confined to the Great Lakes shores (Guire and Voss 1963; Marquis and Voss 1981). The endemic Dwarf Lake Iris {Iris lacustris), which probably came from the south, is a notable exception to this relationship with the north and the west. In their association with open, disturbed habitats and a more-or-less disjunct boreal and western (or co
. The Canadian field-naturalist. Natural history. 1995 Catling and Brownell: Alvars of the Great Lakes Region 157 Manitoulin are part of a large group of plants includ- ing western, cordilleran and boreal disjuncts, which in the Great Lakes region are largely confined to the Great Lakes shores (Guire and Voss 1963; Marquis and Voss 1981). The endemic Dwarf Lake Iris {Iris lacustris), which probably came from the south, is a notable exception to this relationship with the north and the west. In their association with open, disturbed habitats and a more-or-less disjunct boreal and western (or cordilleran) floristic element, the endemics of the upper Great Lakes are similar to the endemics of the Gulf of St. Lawrence (Scoggan 1950; Drury 1969; Catling and Cayouette 1994). This similarity sug- gests the same probable origin; they are probable remnants of a tundra and Picea Parkland flora that existed near the continental ice front in open, cool habitats that resulted from erosion and deposition by ice and water. These species followed the melting continental ice back to the regions of the upper Great Lakes and Gulf of St. Lawrence, and were able to survive in these areas due to the cool, moderate cli- mate and availability of open habitats, such as shore- hnes, cliffs, and rocky barrens. As the continental ice sheet receded further to the north, a colder and more extreme climate was encountered and the extensive blanket of boreal forest developed leaving few open habitats. Thus not all of the flora of the open, ice front habitats was able to survive in, or even to migrate to, the current arctic tundra, and some species were left as relicts in isolated patches of suit- able habitat around the Gulf and the upper Great Lakes (, the largely cordilleran Alaska Orchid {Piperia unalascensis), Figure 11). Some endemics, such as Hymenoxys herbacea, whose closest relatives and centre of diversity are in the west, probably moved in along the periglacial "sidewalk&quo
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