<i>Diplazium subquadripinnatum</i> (Copel.) Lellinger (Athyriaceae): A New Record for the Flora of Niue Resolves an 85‐Year Mystery

A fern collection made by T. G. Yuncker on 27 January 1940 from tropical rainforest forest in Niue had only been identified to its genus and lacked a species determination. Yuncker in his 1943 flora referred the collection to Athyrium Roth, whereas W. R. Sykes in his 1970 flora treated it as Diplazium Sw. Examination of the Yuncker 9916 specimen (BISH!) confirmed it to be correctly placed in Diplazium with the adaxial surface of the rachis and pinna costae with a connected U‐shape channel and the fertile pinnae with elongate sori diagonal to the midvein. Plants matching Yuncker's specimen had not subsequently been collected in Niue until a fortuitous discovery was made in 2025, and DNA sequence data confirmed this specimen is affiliated to D. assimile (Endl.) Bedd. and belongs to sect. Assimilia R. Wei. The morphology of Yuncker's specimen matches D. subquadripinnatum (Copel.) Lellinger, which is distinguished by glabrous, 3–4‐pinnate fronds, pinnules shallowly to deeply lobed, and usually connate with adjacent pinnules and the base decurrent with the pinnae rachis. D. subquadripinnatum is indigenous to French Polynesia, with the Niue record being a significant westward range expansion. Information is provided on the species biostatus, recognition, distribution, and habitats.