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Comparisons of morphology, germination, and establishment success among Dudleya (Crassulaceae)
Premise-Dudleya is a genus of succulent perennials containing about 50 species/subspecies. Many are restricted to narrow geographic ranges, and closely related forms live in differing climates. Dorsey and Wilson (2011) found an intriguing set of correlations among nine Dudleya: species with a smaller mature body size had a lower tolerance for an arid inland climate compared to larger bodied species. I asked if such correlations might represent repeated evolutionary trends across the genus more broadly, mainly in terms of seedling ecology. Methods-To elucidate evolutionary trends, I sampled 10 pairs of close relatives. Judgement of relatedness was based on the phylogeny of Yost et al. (2013) and tight morphological similarity. For each pair, one form was judged to be more mesophilic and the other to be more xerophilic, based on climate of origin. I measured seeds, germination rates, and survival success in two gardens, one coastal and one inland. I gathered field data on the size of mature plants, inflorescence height, etc., and then looked for correspondences. I expected to find for many pairs that the xerophilic taxon would have larger mature body sizes and greater rates of survival than its mesophilic relative. I expected seed size would negatively correlate with plant size and would positively affect germination and survival, and that survival would be higher on the coast. Results-There were no trends between climate-of-origin and the direction of significant differences in the recruitment niche. Plant and seed sizes were non- significantly larger for mesophilic relatives, the opposite of what was expected from Dorsey and Wilson (2011). Polyploid species had significantly larger seeds. Seed size did not predict germination rate. At the coastal garden, germination and seed size predicted survival through the first summer. Three pairs show niche divergence by their significant differences in survival at a garden. The habitat dependence of most taxa is clear, as evidenced by plants surviving significantly better through the summer at the coastal garden than at the inland garden. Conclusions-Trends among closely related species were scarce. I did find many cases of divergence in germination rate or seedling establishment, but I failed to find consistent predictors of the direction of divergence. Quite possibly Dorsey and Wilson's correlations were caused by divergence between two or a very few lineages coupled with phylogenetic conservatism. The various Dudleya forms have evidently diverged, but each in its own way.