Phylogenetics in Scyphostelma (Apocynaceae: Orthosiinae) and description of new species

In the tropical Americas, the Orthosiinae (Apocynaceae) comprises plant species with small but intricate flowers and harbours a tremendous, still understudied diversity currently classified in four genera, Jobinia, Monsanima, Orthosia and Scyphostelma. In this study, we describe and illustrate four new species of Scyphostelma: S. bolivianum, S. gracile, S. rotorum and S. solomonii, based on specimens collected in Bolivia and Peru.

Phylogenetic analysis places S. bolivianum and S. gracile in a clade with S. harlingii, a species from southern Ecuador and central Peru, together as sister clade to the rest of Scyphostelma. Due to the size of flowers and the long-filiform peduncles and pedicels, we consider the two new species S. rotorum and S. solomonii and the new combination S. erikseniae a part of the S. harlingii group, for which an identification key is presented.

Furthermore, four species names are lectotypified and six new combinations in Scyphostelma are made: S. fasciculiflorum, S. jaramilloi, S. purpurascens, S. quitense, S. stenospira and S. unguiculatum.