Ontogenetic and phylogenetic diversification of the hooded staminode in Marantaceae

Abstract

AbstractThe flowers of Marantaceae are known for their unique pollination mechanism mediated by an explosive style movement. The mechanism is based on the highly modified elements of the inner androecial whorl, i.e., the single half‐fertile anther and the fleshy and hooded staminodes. We investigated 67 species across 24 genera to elucidate which parts of the hooded staminode are shared by all species, thus likely under strong selection pressure, and which are allowed to vary. We treated hooded staminodes as character syndromes and grouped them based on gross similarities. We identified characters underlying the similarity and investigated their diversity and developmental pathways. All hooded staminodes correspond in their general morphology, development and vascularisation, suggesting they are homologous. Variable proportions, differential growth and the formation of secondary structures result in a diversity of morphologies. The hooded staminodes can be grouped into ten distinct types. These morphological types are in accordance with the accepted clades of the family indicating their phylogenetic significance. The early diverging clades are characterised by stiff and elaborate staminode structures whereas in more distantly diverging clades simplified forms appear. We conclude that elaborate structures are not essential to maintain the pollination mechanism and thus have been reduced in the course of evolution.