PHYLOGENY OF ELMS (ULMUS, ULMACEAE) - MOLECULAR EVIDENCE FOR A SECTIONAL CLASSIFICATION

The approximately 45 woody species of Ulmus (Ulmaceae) have been place d in five to nine sections on the basis of morphological characters. C ladistic analyses of chloroplast DNA restriction site variation were e mployed to examine phylogenetic relationships among 29 Ulmus accession s, including representatives from all proposed sections and subsection s, and Zelkova serrata. Sufficient variation was detected to construct cladograms with branches both well-resolved and supported. The cpDNA results are largely congruent with those based on nuclear ribosomal DN A. Inclusion of 18 morphological/chemical characters further resolved relationships within the genus. Intrageneric relationships implied by the molecular and combined cladograms differ from previous classificat ions in a number of respects. Three species, U. crassifolia, U. seroti na, and U. thomasii, which have been placed in two or three sections, were found to form a well differentiated monophyletic group (sect. Tri choptelea). The maintenance of sections Anisoptelea and Trichocarpus a nd the recognition of subsections Foliaceae and Glabrae within section Ulmus are not supported. The inclusion of U. mexicana, sometimes trea ted as the distinct genus Chaetoptelea, within Ulmus is supported. The molecular evidence supports the distinctiveness of U. rubra and the r ecognition of two subgenera: Oreoptelea (sects. Blepharocarpus, Chaeto ptelea, and Trichoptelea s. l.) and Ulmus (sects. Lanceifolia, Micropt elea, and Ulmus).