The Phylogenetic Affinities of Two Mysterious Monotypic Mimosoids from Southern South America

Abstract

Abstract Two monotypic genera of Mimosoideae from southern South America, Mimozyganthus and Piptadeniopsis, have been particularly difficult to classify and there has been disagreement about their relationships to other legume genera. We undertook a phylogenetic study based on molecular data from the chloroplast and nucleus, and synthesized it with new data from morphology, cytology, and palynology, in order to determine where these genera belong in the mimosoid phylogenetic tree. Mimozyganthus, an enigmatic genus whose unique morphology led workers to consider it transitional between the subfamilies Mimosoideae and Caesalpinioideae, is instead nested among the higher mimosoids on the molecular tree. Careful evaluation of the characters that were considered to be caesalpinioid-like reveals that they are not identical and are independently derived. Piptadeniopsis is most closely related to Prosopidastrum, a primarily Argentinian genus with lomentiform fruits. This is in close agreement with most morphologi...