Tarennella, a new Pavetteae (Rubiaceae) genus from eastern Madagascar

Abstract

Background – This contribution is part of an ongoing study on the taxonomy and the phylogenetic relationships of the Malagasy representatives of the tribe Pavetteae (Rubiaceae).Material and methods – Taxonomic methods follow normal practice of herbarium taxonomy. A molecular study using the plastid markers rps16, trnT-F, petD, and accD-psa1, the nuclear ribosomal marker ITS and the nuclear MADS-box gene marker PI was executed.Key results – Five new species are described from littoral, lowland, or mid-elevation humid forests in eastern Madagascar. They are characterized by compact inflorescences with small, sessile flowers, a densely pubescent style, large placentas with 2–3 immersed ovules, seeds with a small, superficial hilum not surrounded by a thickened annulus, and pollen grains with supratectal elements. The phylogenetic tree, which included three of the five new species, showed an unresolved backbone but high support for distal nodes grouping species. The new species form a distinct monophyletic clade among the other Malagasy Pavetteae genera and are recognised at genus level under the name Tarennella. Provisional IUCN Red List assessments show that Tarennella homolleana is Vulnerable, T. cordatifolia and T. sanguinea are Endangered, T. puberula is Critically Endangered, and T. coronata is Critically Endangered (Possibly Extinct).