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

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

ANAIS DA ACADEMIA BRASILEIRA DE CIENCIAS.

ACAD BRASILEIRA DE CIENCIAS

Lugar: Rio de Janeiro; Año: 2018 p. 1397 - 1415

0001-3765

Diacrodon is a monotypic genus of the tribe Spermacoceae (Rubiaceae), endemic tonortheastern Brazil. Diacrodon compressus is frequently misidentified with a two lobed calyx species of Borreria, B. verticillata. Traditionally, in Spermacoceae the fruit type was considered a diagnostic character among the genera. In this sense, D. compressus presents a strongly compressed, one seeded and indehiscent fruit (vs. globose, two seeded and dehiscent fruit in B. verticillata). In this work, we address two objectives: evaluating the systematic position and determining the identity of Diacrodon respect to others taxa. Molecular analyses using ITS and ETS indicate that D. compressus is strongly related to another species of Borreria. The morphological results revealed that D. compressus, despite of its type of fruit, is identical to Borreria in floral and palynological features. As conclusion, the new combination Borreria diacrodonta is made and a lectotype is designated. An updated description of the species and a key to the Borreria species with a two lobed calyx are provided. The distribution of B. diacrodonta is extended to Brazilian states Goiás and Minas Gerais, and Paraguay. This taxonomical change it has become clear that the dehiscence of the fruits lack taxonomic value in the delimitation of Borreria.