Although the angiospermous plants are among the best-studied organisms, there are still groups among them whose diversity, distribution and phylogeny are largely unexplored. Prof. Dr. Sigrid Liede-Schumann and PD Dr. Ulrich Meve from the Plant Systematics working group at the University of Bayreuth began studying the little-studied milkweed plants (Asclepiadoideae) of tropical America over 20 years ago. Now, for the first time, they have been able to present a comprehensive overview of the genus Orthosia with 55 species, which is distributed from Florida and Mexico to Argentina.
The work is based on the examination of herbarium specimens and living material. It includes a genetic and phylogenetic analysis of around half of the Orthosia species and a comprehensive description and illustrations of each individual species. Identification keys for each of the three main distribution areas, South America, Central America and the Caribbean, are provided.
Compared to previous estimates, the number of species in the genus Orthosia has almost doubled, which is partly due to the description of new, previously unknown species. One of these new species is Orthosia micrantha from Venezuela, which, with a flower diameter of less than one millimeter, has the smallest flower known to date within its plant family. In addition, the application of modern phylogenetic methods has shown that groups that were previously understood as widespread species are now divided into morphologically very similar, but geographically restricted subgroups that are not directly related to each other.
Available species names, which are linked to a precise species description, represent the key to all known information about a plant, such as distribution, uses and chemical constituents. The revision of the genera of these South American climbing plants by the Bayreuth botanists thus contributes to a better understanding of the composition and evolution of the South American flora.
