Results from work on a phylogeny of the genus Crataegus suggest a possible re-evaluation of the status of Mespilus. Crataegus and Mespilus share a number of wood anatomical and morphological features that set them apart from most other members of Rosaceae subfamily Maloideae. Data for single species of each genus from rDNA internal transcribed spacer regions (ITS1, ITS2) likewise have shown Crataegus and Mespilus to be sister genera, in a clade with Amelanchier, Peraphyllum, and Malacomeles. We report now on sequence variation in ITS1, 5.8S rDNA, and ITS2 in a sample of Crataegus species representing most of the 15 sections of the genus, and both species of Mespilus (Eurasian M. germanica L. and the Arkansas endemic M. canescens Phipps). For outgroups we have used Amelanchier, Malus, and Pyrus. The medlar, M. germanica, appears to be nested within Crataegus; preliminary results suggest that M. canescens could be of hybrid origin. Results may also cast light on relationships between stamen-number morphotypes in North American sections of Crataegus.

Key words: classification, Crataegus, ITS, Mespilus, phylogeny, Rosaceae