Inflorescence structure in the Eriocaulaceae clade of Paepalanthus dimerous-flowered species and allied groups: tackling evolutionary and taxonomic questions

Abstract

Inflorescence morphology is regarded as a tool for the understanding and delimitation of natural groups despite historical confusion and misconceptions. In this manuscript we establish the branching patterns and the homologies of the inflorescences in the clade of Paepalanthus species with dimerous flowers and allied species in order to evaluate their evolutionary and systematic significance. Inflorescences of P. subg. Thelxinoë, P. sect. Conodiscus, P. ser. Dimeri, P. sect. Diphyomene, and Actinocephalus were analyzed into characters and states within a comprehensive, descriptive system. Ancestral character state reconstructions using BayesTraits were performed for relevant characters over a pre-existing phylogeny. Varying from a first-order to a fourth-order structure, inflorescences appear to have an intricate evolutionary history with replication or loss of repetitive units and components, such as the basic units, scapes, and pherophylls. The inflorescence components and branching patterns were found to be highly variable among the species, but very conservative within each category of the current classification system. From a phylogenetic perspective, the characters and states described here, combined with detailed floral studies, are useful for tackling evolutionary and taxonomic concerns, such as the position of the species of P. ser. Dimeri and P. sect. Diphyomene. The approach used here is also appropriate for the family as a whole and is suggested as potentially useful for other angiosperm groups.