Structure of the flower of Simaba (Simaroubaceae) and its anatomical novelties

Abstract

Simaroubaceae are a small, monophyletic family with a mostly pantropical distribution. Although the considerable floral variation found in Simaroubaceae has resulted in some detailed structural studies, no such studies exist for Simaba, the largest genus in the family. We present data on the floral structure of Simaba using a comparative approach, including studies of vascularization and histology. We analysed species of two of the three sections of the genus (Simaba sections Floribundae and Grandiflorae) with the goal of providing characters for studies of taxonomy and phylogeny in the genus. We found several floral structures commonly reported for other genera of Simaroubaceae and closely related groups of Sapindales. We also found some novel structural features in Simaba, such as variation in merism among flowers of the same inflorescence and sexual floral variations related to organ sterility, a condition known in other members of Sapindales, but not previously recorded in Simaroubaceae. We also found partial connation and coherence of the androecium, which forms a pseudotube in species of section Grandiflorae. Finally, the nectariferous feature of the gynophore surface of the studied species was described in detail.