| Four sections of the genus Primula are represented in northern North America: Aleuritia, Armerina, Crystallophlomis, and Cuneifolia. In this dissertation I discuss anatomical, morphological, cytological, ecological, and reproductive characters for thirteen species, and demonstrate coherence of sectional groups through cluster analysis and ordination. In Primula, distyly and homostyly play critical roles in systematics and biogeography. It is generally assumed that distylous individuals are almost completely outcrossed, and homostyles are capable of selfing. In the taxa examined here, distyly exists at the diploid and tetraploid levels while homostyly is seen in both diploids and higher polyploids. I suggest that distyly breaks down with selection for reproductive assurance in environments where pollinators are unreliable, or following hybridization in conjunction with polyploidy. While most northern Primula species are homostylous, several examples of distylous taxa demonstrate that this can be a successful breeding system in higher latitudes. In homostyles, self-compatibility and the proximity of reproductive organs assures a high degree of selfing; however, most northern homostylous taxa also exhibit attributes which suggest facultative outcrossing is common. In North America, evolution in Primula has been strongly influenced by Quaternary events leading to isolation, migration, and secondary contact of gene pools, in association with the breakdown of distyly to homostyly. The success of homostylous taxa is at least partially due to their ability to self-fertilize coupled with the availability of areas to colonize when Pleistocene ice retreated. The phytogeographic affinities, cytology, and reproductive shifts of Primula make it a useful model for processes occurring in the Alaskan flora. The steppes and mountains of Asia have been important source areas, and migration has taken place along mountains, rivers, island arcs, and coastlines. Speciation in the genus has been aided by hybridization, polyploidy, and reproductive diversity. |
