|Costularia cadetii Larridon|
in Larridon, Rabarivola, Xanthos & Muasya, 2019.
A recent molecular phylogenetic study revealed four distinct evolutionary lineages in the genus Costularia s.l. (Schoeneae, Cyperaceae, Poales). Two lineages are part of the Oreobolus clade of tribe Schoeneae: the first being a much-reduced genus Costularia s.s., and the second a lineage endemic to New Caledonia for which a new genus Chamaedendron was erected. The other two lineages were shown to be part of the Tricostularia clade of tribe Schoeneae. Based on morphological and molecular data, the genus Costularia is here redelimited to represent a monophyletic entity including 15 species, which is restricted in distribution to southeastern Africa (Malawi, Mozambique, South Africa, Swaziland, Zimbabwe), Madagascar, the Mascarenes (La Réunion, Mauritius), and the Seychelles (Mahé). Molecular phylogenetic data based on two nuclear markers (ETS, ITS) and a chloroplast marker (trnL-F) resolve the studied taxa as monophyletic where multiple accessions could be included (except for Costularia laxa and Costularia purpurea, which are now considered conspecific), and indicate that the genus dispersed once to Africa, twice to the Mascarenes, and once to the Seychelles. Two endemic species from Madagascar are here described and illustrated as new to science, as is one additional species endemic to La Réunion. Two taxa previously accepted as varieties of Costularia pantopoda are here recognised at species level (Costularia baronii and Costularia robusta). We provide a taxonomic revision including an identification key, species descriptions and illustrations, distribution maps and assessments of conservation status for all species.
The genus Costularia is redelimited to represent a monophyletic entity including 15 species. Although the species diversity is largely found in Madagascar, our results indicate that the genus dispersed once to Africa (Malawi, Mozambique, South Africa, Swaziland, Zimbabwe), twice to the Mascarenes (La Réunion, Mauritius), and once to the Seychelles (Mahé). Three-quarters of the species are threatened with extinction, because of restricted distribution ranges and human impact. A full taxonomic treatment is provided, including an identification key to all species, formal descriptions of two new species from Madagascar (Costularia andringitrensis and Costularia itremoensis) and one new species from La Réunion (Costularia cadetii), and two taxa previously recognised as varieties of Costularia pantopoda are here recognised at species level (Costularia baronii and Costularia robusta).
Isabel Larridon, Linah Rabarivola, Martin Xanthos and A. Muthama Muasya. 2019. Revision of the Afro-Madagascan Genus Costularia (Schoeneae, Cyperaceae): Infrageneric Relationships and Species Delimitation. PeerJ. 7:e6528. DOI: 10.7717/peerj.6528
Top 10 species discovered in 2019
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