Profile of a flower: How rates of morphological evolution drive floral diversification in Ericales and angiosperms.

PREMISE: Recent studies of floral disparity in the asterid order Ericales have shown that flowers vary strongly among families and that disparity is unequally distributed between the three flower modules (perianth, androecium, gynoecium). However, it remains unknown whether these patterns are driven by heterogeneous rates of morphological evolution or other factors. METHODS: Here, we compiled a data set of 33 floral characters scored for 414 species of Ericales sampled from 346 genera and all 22 families. We conducted ancestral state reconstructions using an equal-rates Markov model for each character. We estimated rates of morphological evolution for Ericales and for a separate angiosperm-wide data set of 19 characters and 792 species, creating "rate profiles" for Ericales, angiosperms, and major angiosperm subclades. We compared morphological rates among flower modules within each data set separately and between data sets, and we compared rates among angiosperm subclades using the angiosperm data set. RESULTS: The androecium exhibits the highest evolutionary rates across most characters, whereas most perianth and gynoecium characters evolve more slowly in both Ericales and angiosperms. Both high and low rates of morphological evolution can result in high floral disparity in Ericales. Analyses of an angiosperm-wide floral data set reveal that this pattern appears to be conserved across most major angiosperm clades. CONCLUSIONS: Elevated rates of morphological evolution in the androecium of Ericales may explain the higher disparity reported for this floral module. Comparing rates of morphological evolution through rate profiles proves to be a powerful tool in understanding floral evolution.

Evolution of the coniferous seed scale.

BACKGROUND: The Florin model is the commonly accepted theory of coniferous seed scale evolution. It describes the derivation of extant seed scale morphology from the morphology of fossil conifers via the reduction of complex to simple axillary structures. In this framework the seed scale is composed of a reduced lateral shoot with fertile and sterile appendages which are interpreted as leaf homologues. SCOPE: The Florin model has three crucial problems that we address here: (1) the original derivation series does not take the ontogeny of extant conifers into account, (2) it cannot explain the morphology of all extant conifers and (3) Taxaceae were originally excluded. Examination of seed cones of extant conifers shows that ovules occur in three different positions in the cone: in an axillary position, replacing a leaf or terminating the cone axis. By interpreting the fertile appendage or seed-bearing structure as a leaf, not all positions are possible. The exclusion of Taxaceae from conifers is in stark contrast to recent molecular phylogenetic studies, which include Taxaceae in conifers as sister to Cupressaceae. Therefore, the Florin model does not offer an adequate explanation for taxaceous morphology. CONCLUSION: We conclude that the seed-bearing structure of conifers cannot be interpreted as homologous to a leaf. In the interpretation we present here, the seed-bearing structure is the modified funiculus of the ovule, multiples of which laterally fuse to form the seed scale. The seed scales of all extant conifers can be derived from a Cunninghamia-like morphology via fusion and reduction of individual funiculi.