Taxonomy with an absence of evidence results in unnecessary nomenclatural change: the case of Tetragonia trigyna Banks & Sol. ex Hook.f. (Aizoaceae) from New Zealand

Abstract

ABSTRACT Tetragonia trigyna Banks & Sol. ex Hook.f. was the accepted name for a well-known coastal species in New Zealand from when it was formally named by J. D. Hooker in 1864 until the 1990s. In 1994, a Flora of Australia volume covering Norfolk and Lord Howe Islands reduced T. trigyna to synonymy of the Australian T. implexicoma (Miq.) Hook.f.. This was followed in 1999 by the first acceptance of T. implexicoma in New Zealand botanical literature when the name was used in a checklist of plant species from Aorangi Island, Poor Knights Islands. In a departure from what is generally considered accepted taxonomic practice, no empirical evidence or discussion of characters was provided in support of either decision. Subsequently, T. implexicoma has become widely used in New Zealand. The taxonomic study of T. implexicoma and T. trigyna reported here provides empirical data from herbarium specimens and cultivated plants, and concludes both species should be recognised. Tetragonia trigyna differs from T. implexicoma by its broader leaves, shorter pedicels, shorter tepals, and fewer and shorter stamens. Images in the citizen science iNaturalist platform confirm the diagnostic characters and distribution, and recently published nrDNA ITS sequence data distinguish both species. Accordingly, T. trigyna is reinstated with a distribution of New Zealand (including Chatham, Kermadec and Three Kings islands), Norfolk Island and Lord Howe Island, and T. implexicoma is considered restricted to continental Australia and Tasmania.