A colony of a fern, Lygodium hians E.Fournier (Schizaeales), studied on the southwest Pacific Island of New Caledonia, displays a growth form unusual for any member of this genus. Other living species of the genus Lygodium Sw. are characterized by twining fronds, with indefinite growth, which climb extensively on the support provided by other nearby vegetation. These fronds can arise from as early as the sporeling stage and fulfil both vegetative and reproductive functions, with spores produced in lateral sorophores in the upper parts of the fronds. By contrast, in L. hians, climbing fronds are only rarely produced and these carry terminal to subterminal sorophores. The main vegetative growth is of a low-growing (here termed ‘ground-clothing’) frond-type, of definite, rather than indefinite, growth and of unusual dichotomous blade structure. This life form has survived, in this rare and little known remote species, under conditions of considerable ecological, as well as geographic, isolation in the mountains of New Caledonia. Blade/pinnule abscission occurs in L. hians in both ground-clothing and climbing fronds, therefore shed foliar units in the fossil record do not imply that ancient Lygodium were climbers. The features of L. hians, uniquely within Lygodium, provide morphological links with Schizaea Sm. and Actinostachys Wall. The morphology considerably expands our concept of variation in the genus Lygodium and suggests that this life form today may represent an evolutionary phase near to the early stages of diversification of the genus. For these reasons L. hians is worthy of inclusion in future molecular and morphological phylogenetic analyses and should be incorporated in comparative studies by palaeobotanists studying fossil ferns.
Schizaeales, Lygodiaceae, ground-clothing fern, New Caledonia, morphology, Lygodium evolution