Additions to the Fern Flora of Niue (Polynesia): First Records of Ophioglossum lusitanicum L., Ophioderma falcatum (C.Presl) O.Deg. and Psilotum complanatum Sw. and the Disjunct Occurrence of Ophioderma intermedium (Hook.) Nishida

During recent field survey for threatened and uncommon vascular plants in Niue, four ferns were collected and confirmed as additions to the indigenous flora. Ophioderma intermedium (Hook.) Nishida and O. falcatum (C.Presl) O.Deg. were collected from terrestrial habitats in primary tropical forest. Plants of both species were growing amongst forest floor leaf litter. The distribution of O. intermedium is recognised as S. E. Asia, northern‐most Australia and Melanesia, and the range expansion into Polynesia is of biogeographic significance since Niue is a solitary and isolated oceanic island of only 259 km 2 . The nearest population(s) are to the west of Niue on Bougainville Island, Papua New Guinea, some 4000 km distant. Other achipelagoes, such as Vanuatu, Solomon Islands, Fiji, Samoa and Tonga, should be considered locations where O. intermedium may occur. A regional conservation assessment of Critically Endangered is applied to the Niue populations of O. intermedium and O. falcatum . Ophioglossum lusitanicum L. and Psilotum complanatum Sw. are also new records for the flora of Niue. The diminutive O. lusitanicum occurs in old gravel extraction pits where it is usually associated with the cynobacteria Nostoc commune , and P. complanatum has been collected from forest habitats.