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

Abstract

Premise of the Study: 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 dataset of 33 floral characters scored for 414 extant ericalean species sampled from 346 genera and all 22 families. We conducted ancestral state reconstructions using an equal rates Markov models for each trait. We used the rates estimated during the ancestral state reconstruction for comparing evolutionary rates between flower modules, creating a rate profile of ericalean flowers. Key Results: The androecium exhibits the highest evolutionary rates across most characters, whereas most perianth and gynoecium characters evolve slower. High and low rates of morphological evolution can result in high floral disparity in Ericales. Analyses of an angiosperm-wide floral dataset 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. We discuss the implications of heterogenous morphological rates of evolution among floral modules from a functional perspective. Comparing rates of morphological evolution through rate profiles proves to be a powerful tool in understanding floral evolution.

The ontogeny of disparity in Cupressaceae seed cones

“…In particular, we might expect greater diversity and/or more clustered morphologies at pollination due to the selection of specific floral morphologies associated with different animal pollinators (Berg, 1960; Nilsson, 1988; Cresswell, 1998; Gong & Huang, 2009). Quantifying angiosperm disparity changes over ontogeny is challenging because floral and fruit morphologies are difficult to directly compare; in particular, perianth and androecium organs are major components of floral disparity (Chartier et al ., 2017; Herting et al ., 2023) but are typically shed during fruit development and thus cannot be measured at maturity. Nonetheless, studies that have compared floral and fruit morphology suggest greater morphological diversity at pollination (Whitney, 2009), consistent with the idea that the ontogenetic fitness landscape of angiosperms is different than that of wind‐pollinated conifers and more complex in its early stages.…”

“…Gould, 1991; Briggs et al ., 1992; Foote, 1994; Hughes et al ., 2013; Deline et al ., 2018; Cole & Hopkins, 2021) but in plants as well (Lupia, 1999; Boyce, 2005; Leslie, 2011b). Morphological disparity patterns have also been used to characterize the immense diversity of extant angiosperm flowers (Stebbins, 1951; Chartier et al ., 2014, 2017) and explore how this diversity has evolved in relation to pollination biology (Dellinger et al ., 2019), macroecological variables (Chartier et al ., 2021), and diversification processes (Vasconcelos et al ., 2019; Herting et al ., 2023).…”