Dickinson, Timothy A. , Lo, Eugenia , Talent, Nadia .
2006 - Lewis and Clarks black-fruited hawthorns 200 years later.
BLACK-FRUITED hawthorns (Crataegus section Douglasianae Loudon) were discovered by Europeans in the Pacific northwest as early as 1792, when a Spanish expedition visited Nootka, on Vancouver Island. Collections were made by Lewis and Clark in 1806, and by David Douglas in 1825-1826. Douglas sent seeds back to England where they were grown out by the Horticultural Society; after his death in 1834 Lindley illustrated the Horticultural Society plant and named it in Douglas' honor. Douglas' herbarium material demonstrates what illustrations show, namely that these North American black-fruited hawthorns comprise two morphotypes, one with 20 stamens per flower (Echeverrķa ca. 1792) and the other with 10 stamens (Watts 1835). These illustrations notwithstanding, this distinction was not recognized until 1907, when C. S. Sargent described Crataegus douglasii var. suksdorfii. Only in the past 40 years has our understanding of these plants advanced substantially beyond that of Sargent and Wilhelm Suksdorf. It turns out that the 20-stamen variety comprises triploids and tetraploids as well as diploids, while the 10-stamen variety apparently consists exclusively of tetraploids. Flow cytometric estimates of ploidy level from leaf tissue, embryos, and endosperm confirm earlier embryological observations indicating that polyploid C. douglasii reproduces by gametophytic apomixis. Moreover, analyses of over 200 alleles at 13 microsatellite loci suggest that the polyploids have arisen repeatedly. We believe the pattern of relationships seen can be interpreted in the light of results from experimental pollinations (in other sections of the genus) as evidence of reticulation involving all three ploidy levels. Based on these results, as well as phylogenetic analyses of DNA sequence data reported elsewhere and morphometric analyses of type specimens, a revised classification of section Douglasianae has been proposed.
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North American black-fruited hawthorns
1 - Royal Ontario Museum - Green Plant Herbarium (TRT), Department of Natural History, 100 Queen\'s Park, Toronto, Ontario, M5S 2C6, CANADA
2 - University of Toronto, Department of Botany, 25 Willcocks Street, Toronto, Ontario, M5S 3B2, Canada
Presentation Type: Array
Location: 134/Performing Arts Center
Date: Tuesday, August 1st, 2006
Time: 8:30 AM