HUFFORD, LARRY. School of Biological Sciences, Washington State University, Pullman, WA 99163. - Ontogenetic evolution and patterns of morphological diversity.
Comparative studies of development, especially those that apply robust
reconstructions of organismal phylogeny, can be used to explore not
only the ontogenetic changes that create diversity but also how the
patterning of diversity in clades emanates from the succession of
ontogenies that compose lineages. Androecial diversity and development
has been investigated in the sister families Hydrangeaceae and
Loasaceae, which have similar levels of taxonomic richness. Both
families have clades characterized by haplostemonous, diplostemonous,
and polystemonous androecial states; however, the patterning of
androecial diversity is considerably different in the two families.
Hydrangeaceae have diversity centered largely in homoplastic shifts
between diplostemony and polystemony. Novelties in the androecium of
Hydrangeaceae are limited largely to the formation of filament flanges
in the diplostemonous Fendlera and Deutzia and to
elaborations that facilitate a substantially higher number of stamens
in Carpenteria. Androecia of Loasaceae differ markedly in
having a highly divergent pattern of androecial diversity. Loasaceae
androecia have diversified largely through the origin of novelties.
Novelties occur in fertile stamens, including the origin of filament
flanges in selected Mentzelia and differentiation in anther
size and stomium extent in Schismocarpus. Several novelties in
Loasaceae involve the differentiation of the androecium into fertile
and nonfertile (staminodial) regions. Each origin of staminodes has
been associated with a differing mode of ontogenetic evolution.
Key words: development, diversity, Hydrangeaceae, Loasaceae, morphology, ontogeny