Specialization to ultramafic substrates and narrow endemism of Cyclophyllum (Rubiaceae) in New Caledonia: contribution of novel species to the understanding of these singular patterns

New Caledonia, listed as a biodiversity hotspot, is ecologically unique because of the abundance on the main island of ultramafic soils. The Pacific genus Cyclophyllum Hook.f. (Rubiaceae) that belongs to the tribe Vanguerieae has its centre of diversity in New Caledonia, with 13 species described so far. The present taxonomic treatment describes seven species new to science: Cyclophyllum guillauminianum Baum.-Bod. ex Mouly & Jeanson, Cyclophyllum letocartiorum Mouly, Cyclophyllum macphersonii Mouly, Cyclophyllum memaoyaense Mouly, Cyclophyllum pindaiense Mouly, Cyclophyllum tieaense Mouly and Cyclophyllum tiebaghiense Mouly & Jeanson. These new species, all endemic to New Caledonia add to species already described for the genus. A determination key and few synonymies are provided here. These species present a very interesting pattern of narrow endemism probably resulting from adaptation(s) to ultramafic substrates. Indeed, 14 species out of 19 are restricted to constraining soils and 12 species are narrow endemics to diverse areas of the main island. The category of threat was evaluated for the new species and as a result several of the described species should be considered for conservation.