Phylogenetic position and evolution of glandular structures of the unusual and narrowly distributed genus Rhytidanthera (Ochnaceae)

Abstract

Rhytidanthera is the only genus of Ochnaceae with compound leaves, and it forms sparse, small populations restricted to the primary forest of the Colombian and Venezuelan Andes and the sandstone hills of La Macarena and Chiribiquete. It has been suggested to be related to Godoya, Cespedesia and Krukoviella in taxonomic and phylogenetic studies. However, the relationships in this group remain poorly resolved, due to the lack of a wider molecular and taxonomic sampling. We present a phylogenetic study of tribe Sauvagesieae including three Rhytidanthera spp. and one species each of Godoya and Cespedesia, using sequences from one nuclear (ITS) and four plastid DNA regions (matK, ndhF, rbcL and trnL-F), in order to clarify the relationships among these four genera. We recover a new and well-supported phylogenetic hypothesis, with Rhytidanthera as sister to a clade comprising Godoya and the clade formed by Cespedesia and Krukoviella. This Neotropical clade was recovered as sister to the monotypic and African genus Fleurydora. The clade comprising Rhytidanthera, Godoya, Cespedesia and Krukoviella is supported by the presence of glandular structures (colleters) at the base of stipules and bracts. The colleters also evolved at the base of the sepals in this clade, with a secondary loss in Cespedesia and Krukoviella. We suggest that the combination of unequal-sized sepals enclosing the floral bud and the presence of colleters in members of this clade could have a role in the protection of leaves and flowers in the early stages of development, instead of acting in pollinator attraction.