Systematics Section / ASPT
Lo, Eugenia , Stefanovic, Sasa , Dickinson, Timothy A. .
Intrageneric classification and biogeography of the genus Crataegus (Rosaceae) based on nuclear and chloroplast sequences.
AROUND the world, there are about 150 Crataegus species distributed across the northern temperate zone. Taxonomically, they are divided into 15 sections and 33 series based on morphology. Phylogenetic relationships within Crataegus (tribe Pyreae) have been investigated with a combination of four chloroplast (trnG-trnS, psbA-trnH, trnH-rpl2, rpl20-rps12 spacers) and two nuclear loci (ITS1-5.8S-ITS2 and second intron of LEAFY). Sixty-eight Old and New World species of Crataegus, together with species of Amelanchier, Malus, and Aronia as outgroups, yielded molecular data that divide Crataegus taxa into six major clades and show less sectional resolution than does the morphological classification. The clades that resulted in maximum parsimony, Bayesian and maximum likelihood analyses, comprise, respectively, taxa from four distinct geographical regions. Taxa from East Asia section Sanguineae and Western North America sect. Douglasianae are resolved separately in two monophyletic clades and are sister to each other. Taxa from Eastern North America that are morphologically divided into six sections, including Coccineae, Crus-galli, Parvifoliae, Mexicanae, Virides, and Lacrimatae, are unresolved forming a large polytomy. One of two East Asian monotypic sections sect. Hupehensis is closely associated with the European members of section Crataegus. Significant incongruence is observed in the placement of C. marshalli (sect. Crataegus, ser. Apiifoliae), C. spathulata (sect. Microcarpae), and C. phaenopyrum (sect. Cordatae) between the nuclear and chloroplast trees. We suggest that these taxa could have arisen from the crosses between ancestral Eurasian and American taxa. DIVA analyses indicate the occurrence of at least 8 independent dispersal/extinction events within the genus as a whole. Based on ITS substitutions, such movements involve the intercontinental exchange between the European and North America taxa as early as 47.4 million years ago, and the more recent trans-Beringian migration between Eastern Asia and Western North America around 19.3 million years ago.[c.e.:srb]
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1 - University of Toronto, Department of Botany, 25 Willcocks Street, Toronto, Ontario, M5S 3B2, Canada
2 - University of Toronto at Mississauga, Biology, 3359 Mississauga Rd N, Mississauga, Ontario, L5L1C6, Canada
3 - Royal Ontario Museum, Centre for Biodiversity and Conservation Biology, Royal Ontario Museum 100 Queen's Park, Toronto, Ontario, M5S 2C6, Canada
Presentation Type: Oral Paper:Papers for Sections
Location: 134/Performing Arts Center
Date: Tuesday, August 1st, 2006
Time: 8:15 AM