What reproductive traits tell us about the evolution and diversification of the tree-of-heaven family, Simaroubaceae

Floral features contribute with remarkable additions to morphological studies and are widely used to address questions about the evolution and diversification of several groups of plants. Even though Simaroubaceae are a small monophyletic family, the few detailed structural analyses of reproductive organs and the floral diversity and variations already described in their members stimulate novel structural studies. In this study, we investigate the evolution of reproductive features of Simaroubaceae by means of a combination of original data and a review of the literature, aiming to elucidate which floral characters are most informative for a better understanding of the evolutionary history of the group. We analyzed 21 out of the 23 genera of Simaroubaceae, plus six from Rutaceae and seven from Meliaceae as outgroups. We used a Bayesian method and the Parsimony optimality criterion to reconstruct ancestral reproductive character states using a re-analyzed phylogenetic tree of Sapindales. Here, we combined available molecular sequences to have the largest sample of Simaroubaceae genera. We found that the ancestral flowers of Simaroubaceae were probably polygamous or dioecious plants, with free carpels united only distally, with divergent, elongated stigmas, and with drupaceous, laterally flattened to lenticular fruits. The latter feature plus apocarpous carpels are putative synapomorphies of the family retrieved in this study. Imbricate petals and a diplostemonous androecium were recovered as conditions found in the ancestor of Simaroubaceae but also shared with the ancestors of Meliaceae and Rutaceae. Our findings were mostly in accordance with previous evolutionary studies on genera of Simaroubaceae and with other families of Sapindales.