Phylogenetic placement of Cailliella praerupticola (Melastomataceae), a rare, monospecific lineage from Guinea, West Africa

Abstract

The genus Cailliella includes a single species, C. praerupticola, restricted to a sandstone plateau region in Coyah, Dubreka, Forécariah and Kindia Préfectures, Guinea, West Africa. Until its rediscovery in 2016, this species was known only by the type gathering made in 1937. We provide an emended description, photographs of living material, locality and habitat data, and a discussion of its conservation status. We further designate a lectotype for C. praerupticola. On the basis of morphology, Cailliella had been considered an isolated member of the tribe Melastomateae, possibly sister to Melastomastrum. We tested the classification of Cailliella by means of a phylogenetic analysis of C. praerupticola and 40 other samples of African Melastomateae, based on molecular sequence data from the external and internal transcribed spacer regions of nuclear ribosomal DNA (nrETS and nrITS) as well as the ndhF, psbK-psbL and accD-psaI regions of chloroplast DNA. Our results corroborate the placement of Cailliella in the Melastomateae, where it was resolved as sister to a clade consisting of both Melastomastrum and Tristemma. The hypothesis of C. praerupticola being an evolutionary relict or "palaeoendemic"is supported by our findings.