CLADISTIC-ANALYSIS OF RESTRICTION SITE VARIATION WITHIN THE CHLOROPLAST DNA INVERTED REPEAT REGION OF SELECTED HAMAMELIDIDAE

A cladistic analysis was conducted on restriction site variation in the inverted repeat region of the chloroplast DNA of 34 taxa, including 22 genera of Hamamelididae, nine genera of Rosidae, and one genus of Magnoliidae (sensu Cronquist). Parsimony analysis of 45 informative characters resulted in four equally parsimonious cladograms. In all trees, Hamamelididae were polyphyletic, with the rosid taxa nested within ''lower'' hamamelids and ''higher'' hamamelids in turn nested within this rosid group. The ''higher'' Hamamelididae (excluding Leitneria but including Betulaceae, Casuarinaceae, Fagaceae, Juglandaceae, Myricaceae, Nothofagaceae) were monophyletic in all of the most-parsimonious trees, and were always a sister group of Malus (Rosaceae). Within the ''higher'' hamamelid group, Nothofagus was found to be the sister taxon of the remainder of the taxa, supporting recognition of the family Nothofagaceae. The genera of Fagaceae s. str. formed a monophyletic group and were a sister group of the remainder of the ''higher'' hamamelids excluding Nothofagus. The sister group of the rosid-''higher'' hamamelid clade in all trees was a clade that included Liquidambar, Cercidiphyllum, and representative genera of Hamamelidaceae s. str. The analysis showed Euptelea to be the basal taxon of ''lower'' hamamelids, whereas Trochodendron was identified as sister taxon to a larger clade comprised of Hamamelidaceae, Cercidiphyllum, rosids, and ''higher'' hamamelids. Cercidiphyllum was shown to be closely related to Hamamelidaceae s.l., whereas Platanus was placed several nodes away from this clade. This analysis supports recent contentions that Hamamelididae sensu Cronquist is not monophyletic. Our results contradict recent suggestions based on fossil leaves that Fagaceae are derived directly from a platanoid ancestor.