North American silene trait medians

Combinations of correlated floral traits have arisen repeatedly across
angiosperms through convergent evolution in response to pollinator
selection to optimize reproduction. While some plant groups exhibit very
distinct combinations of traits adapted to specific pollinators (so-called
pollination syndromes), others do not. Determining how floral traits
diverge across clades and whether floral traits show predictable
correlations in diverse groups of flowering plants is key to determining
the extent to which pollinator-mediated selection drives diversification.
The North American Silene section Physolychnis is an ideal group to
investigate patterns of floral evolution because it is characterized by
the evolution of novel red floral color, extensive floral morphological
variation, polyploidy, and exposure to a novel group of pollinators
(hummingbirds). We test for correlated patterns of trait evolution that
would be consistent with convergent responses to selection in the key
floral traits of color and morphology. We also consider both the role of
phylogenic distance and geographic overlap in explaining patterns of
floral trait variation. Inconsistent with phenotypically divergent
pollination syndromes, we find very little clustering of North American
Silene into distinct floral morphospace. We also find little evidence that
phylogenetic history or geographic overlap explain patterns of floral
diversity in this group. White and pink flowering species show extensive
phenotypic diversity but are entirely overlapping in morphological
variation. However, red flowering species have much less phenotypic
disparity and cluster tightly in floral morphospace. We find that red
flowering species have evolved floral traits that align with a traditional
hummingbird syndrome, but that these trait values overlap with several
white and pink species as well. Our findings support the hypothesis that
convergent evolution does not always proceed through comparative
phenotypic divergence, but possibly through sorting of standing ancestral
variation.