Phenetic Analyses and Revised Classification of the Ptelea trifoliata Complex (Rutaceae)

The current classification of Ptelea divides the widespread and highly variable Ptelea trifoliata L. into 5 subspecies and 11 varieties, while additionally terming many specimens “intermediate.” Although there are visually observable differences among regional variants, principal component analyses of quantitative characters failed to separate subspecies or to even incompletely separate most varieties within subspecies. Some recognized subgroups are also not well distinguished by discontinuous qualitative characters. Where multiple varieties appear to be part of a single continuum of variation or are extremely similar, it is suggested that a reduction in the number of infraspecific taxa would improve the utility of the classification. An alternative classification recognizing 5 subspecies and 7 varieties is accordingly proposed.