Deux espèces nouvelles de Thiollierea (Rubiaceae) restreintes aux sols hypermagnésiens du massif du Boulinda (Nouvelle-Calédonie)

Two new species of Thiollierea (Rubiaceae) endemic from New Caledonia are described and illustrated. A key to all species of the genus Thiollierea is provided. Thiollierea rigaultii sp. nov. and T. dagostinii sp. nov. belong to the group of Thiollierea with white and purplish flowers. Thiollierea rigaultii sp. nov. has several unique morphological characters, never recorded before in the group: 1-flowered inflorescences, colleters totally covering the internal face of the calyx, and large and coriaceous corollas. Thiollierea dagostinii sp. nov. is characterized by a new and original combination of morphological characters: colleters totally covering stipules adaxially, sub-winged hypanthium, calyx tube obvious without secondary tear, hirsute and cylindrical filament indumentum. Both species are endemic to Boulinda, an ultramafic massif on the North-Western coast of New Caledonia. Their populations are restricted to small forest edges, on hypermagnesian soils, where microendemism is important. The evaluation of IUCN status of these two rare species placed them in the category “critically endangered” (CR).