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Disjunct Species: Separated by Long Distances


"Disjunct species" are those that exhibit unusually wide gaps within their overall distribution.

The Gulf of St. Lawrence region of eastern Canada is very rich in disjunct plant species. A large number of these occur within the "limestone regions" of the Island of Newfoundland.

Two examples:
    The Dwarf Hawk's Beard (Crepis nana) is a plant of the Arctic (ranging from Siberia to Baffin Island) and the mountains of western North America. In eastern Canada, there are a very few tiny "disjunct" populations in the Torngat Mountains of northern Labrador and at Burnt Cape on the northern tip of the Island of Newfoundland.

    Mackenzie's Sweetvetch (Hedysarum boreale subsp. mackenzii) is found primarily from Alaska south to the extreme northwestern United States and east to the eastern shores of Hudson's Bay. There are also small disjunct populations on Anticosti Island in the northern Gulf of St. Lawrence, and on the "limestone barrens" of the western tip of the Port au Port Peninsula, on the Island of Newfoundland [see: status report].
When things get tricky:

Bodin's Milkvetch (Astragalus bodinii) is found primarily in the mountains and foothills of central and northwestern North America - its main population straggling only as far east as Manitoba and Nebraska. However, on the Island of Nefoundland, there is a single, tiny, population, growing almost at sea-level, on the "limestone barrens" at Cook's Point, Cook's Harbour that is separated from the western populations by 2700 km! [see: status report]. But, are our Newfoundland plants exactly the same as the plants represented in the western populations? Merritt Lyndon Fernald certainly didn't think so when he originally described the Cook's Point plants (Fernald 1926: 214-215) as a new species (Astragalus stragalus) on a number of physical characteristics. The fact that the Newfoundland plants grow in a completely different habitat (seaside versus upland) is a particular point to consider. If new studies eventually support Fernald's original conclusions, the resulting seperate species (or subspecies?) would no longer be a DISJUNCT, but, rather, an ENDEMIC!







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