A review of hybridization in north American hawthorns -: Another look at "the Crataegus problem"'

The study of nearly 400 syntype, other type, and probable type elements of Crataegus, in the context of over 4000 other Missouri specimens examined for tire Flora of Missouri Project, provided a unique opportunity to look at putative hybridization in the Missouri Crataegus flora. These specimens collectively represent essentially all the taxonomic variation observed to date for the state. Each type specimen was studied and then categorized as being either: (a) a primary species (orihospecies); (b) a synonym of an orthospecies; or (e) representing a wide hybrid (nothospecies). These nothospecies, all putative, constitute the totally of alleged hybrids for Missouri. Computation of hybrid frequency yielded the conclusion that wide hybrids Occur between about 154 of the possible interserial combinations, and field and herbarium studies show, that Populations of these hybrids are usually small and non-persistent. Working with weaker data, roughly similar results Were generated for the whole of the Crataegus-rich northeastern quadrant of the United States (and adjacent Canada). Interestingly, the very small surviving, or even extinct, nature of the populations of these hybrids, together with then-high reliability of Correct identification, indicate thin known hybrids do not coniribute significantly) to "The Crataegus Problem" routinly touched by North American authors.