Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The thesis defended in this dissertation asserts that individuals of Crataegus series Rotundifoliae (Rosaceae, Maloideae) in southwestern Ontario are members of an agamic complex and that the complex patterns of morphometric variation displayed by the series are a consequence of the reproductive behavior of agamic complexes. The specific problem addressed here arises out of a recognition that the longstanding taxonomic difficulty encountered in the series (and in the genus) can only be solved through intensive cytological, histological and numerical study of local populations.;Cluster Analysis, using a combination of resemblance measure-cluster method combinations, revealed the presence of four groups in a collection of 112 randomly sampled individuals evaluated for 29 morphological descriptors. These four groups and the populations into which they were subdivided display wide differences in levels of variability (univariate descriptor variances and multivariate dispersion determinants) as well as in patterns of descriptor importance in Analysis of Dispersion Structure, Principal Components Analysis and Multi-group Discriminant Analysis. Members of the four groups are all apparently pseudogamous, facultative agamosperms with high pollen viability. All are apparently polyploid (mostly tetraploid with a few triploids) and self-fertile.;Taxonomic analysis, including the use of Cluster Analysis and Principal Components Analysis demonstrated that, in the study area, the series consists of six species, one of which (C. ?lumaria) is presumed to be of hybrid origin. The patterns of morphometric variation displayed by members of these species are related, in general, to a facultative apomictic mode of reproduction, and specifically to patterns of dispersal and to the postulated origin of the species within the agamic complex.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.