Phipps, James B. .
Biogeographical analysis of Montana Crataegus (Rosaceae) east of the Continental Divide.
Examination of 207 herbarium specimens from the Montana montane islands, including those from ongoing fieldwork, demonstrated seven Crataegus species. Hawthorns of this region are shade-intolerant mesophytes concentrated in the lower parts of the highlands between 1000 and 1900 m, preferentially occurring on fine-grained, moisture-retentive soils. Three of the red-fruited species, Cc. chrysocarpa, macracantha and sheridana, the first two very widespread, sometimes survive in favored sites in the open Great Plains. Two black-fruited species, Cc. douglasii and castlegarensis, are also widespread but restricted to montane areas in Montana. All the above occur in most montane islands suggesting relative ease of earlier Holocene dispersal between them; their widespread nature suggests considerable age. One black-fruited species (C. cupressocollina) and one red-fruited (C. ursopedensis) are restricted to the significantly isolated Bears Paw Mountains in Montana and Cypress Hills of Canada but absence from the nearby Sweet Grass Hills (rich in conifers) and Little Rockies suggests difficulty traversing the intervening terrain and perhaps relict distributions. The Bears Paws were not covered by the continental ice-sheet but the Cypress Hills were nearly fully glaciated during the Wisconsonian; nevertheless, these two areas are the most speciose. The concentration of Crataegus individuals and species in the Cypress Hills parallels that in the Okanagan of British Columbia, both being near the north of the range of many species and having substantial areas of favorable mesic habitat. However, difficulty of lateral or northward migration appears to have created geographical culdesacs with evolutionary potential. Putative endemic Crataegus found in both areas have no fossil record but Nadia Talent reports that all Cypress Hills taxa examined exhibit apomixis and tetraploidy. Holocene origin now seems likely for most putative endemics but harder evidence is needed. Refugia for the widespread species have to have been to the south and southwest.
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1 - University of Western Ontario, Department of Biology, 1151 Richmond St., London,, Ontario,, N6A 5B7,, Canada
Presentation Type: Poster:Posters for Topics
Location: Ball Room & Party Room/SUB
Date: Monday, July 28th, 2008
Time: 12:30 PM