Abstract
The fern genus Lastreopsis has been recently re‐circumscribed to include about 19 species. It occurs from southern Asia through the Pacific to the Neotropics, with Australasia having the most species. We here describe a new species endemic to New Caledonia's Grande Terre, L. abscondita . Morphological comparisons and phylogenetic analyses of chloroplast DNA sequences show that L. abscondita resembles and is closely related to L. vieillardii , also endemic to New Caledonia. From L. vieillardii , L. abscondita differs most noticeably in being much scalier, particularly on its rachis and costae, and in having larger scales, and larger, more‐divided fronds. Chloroplast DNA sequences distinguish samples of L. abscondita as a clade, but indicate there is substantial genetic variation within the narrowed circumscription of L. vieillardii such that it is paraphyletic; this should be further investigated. Lastreopsis abscondita is known from only two sites, both at high elevation on non‐ultramafic substrates on Grande Terre. We propose an IUCN conservation status of Vulnerable for L. abscondita , particularly because of the small number of sites and limited area of occupancy. The specific epithet alludes to the fact that this large fern, with fronds over 1.5 m long, has been overlooked until now. This is another indication that the ferns of New Caledonia warrant further study, with more discoveries likely to be made.