The monotypic Brazilian genus Diacrodon is a synonym of Borreria (Spermacoceae, Rubiaceae): morphological and molecular evidences

LAILA M. MIGUEL; STEVEN DESSEIN; SANDRA V. SOBRADO; JANSSENS, STEVEN; ELSA L. CABRAL

Copenhague

Conferencia; VIII International Rubiaceae and Gentianales Conference; 2017

Københavns Universitet

Diacrodon is a monotypic genus of the tribe Spermacoceae (Rubiaceae), which is endemic to Brazil. The name of the only species Diacrodon compressus refers to the strongly compressed, one seeded and indehiscent fruit. This fruit type was considered enough to describe Diacrodon as a different genus in the tribe Spermacoceae, but its author Sprague recognized the similarity with Borreria verticillata. In the present study, we discuss and illustrate the morphology of flowers, fruits, seeds and pollen grains of Diacrodon and the two most similar species of Borreria. Morphological comparisons revealed that Diacrodon compressus is not significantly different from Borreria verticillata and B. spinosa. Additionally, a molecular phylogenetic study was made, using ITS and ETS dataset, to determine the position of Diacrodon in respect to other genera of Spermacoceae tribe. Diacrodon compressus appears strongly related to another species of Borreria. Therefore, D. compressus is considered as a new synonym of Borreria. The new combination Borreria diacrodonta is made and a lectotype is designated. In addition a detailed description of the species is given with illustrations, distribution map and conservation status.