The Ulmaceae, one family or two? Evidence from chloroplast DNA restriction site mapping

The Ulmaceae is usually split into two subgroups, referred to as either tribes or more commonly subfamilies (Ulmoideae and Celtidoideae). The two groups are separated, with some exceptions, on the basis of leaf venation, fruit type, seed morphology, wood anatomy, palynology, chemistry, and chromosome number. Propositions to separate the two groups as distinct families have never gained general acceptance. Recent morphological and anatomical data have suggested, however, that not only is family status warranted but that Celtidaceae are more closely related to Moraceae and other Urticales than to Ulmaceae. In order to test these alternative sets of relationships, restriction site mapping of the entire cpDNA was done with nine rare cutting enzymes using 11 genera of Ulmaceae s. 1., three other families of the Urticales, and an outgroup family from the Hamamelidae. Cladistic analysis of the data indicates that Ulmaceae s. 1. is not monophyletic and that distinct families (Ulmaceae and Celtidaceae) are warranted; that Ulmaceae is the sister group to Celtidaceae plus all other families in the order; and that Cannabaceae might be nested within Celtidaceae. Familial placements of various problematic genera (e.g. Ampelocera, Aphananthe) are resolved and character evolution of key morphological, anatomical, chemical, and chromosomal features are discussed.