Isopterygium albescens (Hook.) A.Jaeger Bericht über die Thätigkeit der St. Gallischen Naturwissenschaftlichen Gesellschaft 1876-77: 433 (Gen. Sp. Musc. 2: 1251) (1878). Isopterygium sarasinii Thér. Nova Caledonia, Forschungen in NeuCaledonien und auf den Loyalty-Inseln, B. Botanik 1: 31 (1914). — Type: Loyalty Islands, Lifou, 1912, Sarasin & Roux 768, 769, (holo-, PC[PC0094059!]) syn. nov. COMMENTS Thériot (1914) described the new species Isopterygium sarasinii as intermediate between I. neocaledonicum Thér. and I. austropusillum (Müll.Hal.) A.Jaeger, that both became synonyms of I. albescens, together with I. minutirameum (Müll.Hal.) A.Jaeger, also recorded for the country (Iwatsuki & Ramsay 2009).Indeed, our observation of the type of I. sarasinii at PC, with the vegetative and perichaetial leaf shapes, the sporophyte characters and the sizes of all parts being included in the variability of I. albescens, lead us to reduce it in synonymy with the latter species. The specimen kept in PC is handwritten by Thériot, annotated “sp. nov.” and “fig.”, meaning a drawing by the author (unpublished). It was sent by the Zurich Botanical Museum in order to determine the mosses collected in New Caledonia by K.F. Sarasin during a Swiss mission with J. Roux in 1911-1912. In the publication of the results, Thériot (1914) designated this specimen as the type but not the herbarium localisation. The specimen in PC (PC0094059) is most likely the only plant used by Theriot for its description of the new species and, therefore, the holotype. Finally, in New Caledonia there is only one species of the genus Isopterygium. The two more reported Isopterygium, I. arquifolium (Bosch et Sande Lac.) Jaeger and I. textorii var. latifolium Cardot & Thériot, now belong to a different genus (see below: Pseudotaxiphyllum pohliaecarpum).

Published as part of Thouvenot, Louis & Müller, Frank, 2021, Contribution to the bryophyte flora of New Caledonia IV. Species new to the country, new localities together with taxonomic notes, pp. 181-196 in Cryptogamie, Bryologie 20 (13) on pages 189-190, DOI: 10.5252/cryptogamie-bryologie2021v42a13, http://zenodo.org/record/7822275