(h.) Isolation on the Main Islands.
Endemism is not confined to isolated islands, but the various floral districts contain their peculiar species and forms. The most striking examples are western Nelson and western Otago, with thirty-three and thirty-eight endemic species respectively. The northern part of Auckland (thirteen species), Marlborough (fourteen species), and other localities show a distinct local endemism. It is obvious, then, that a strong endemism can exist apart from such a barrier as a wide stretch of ocean. But figures such as the above are not final; further investigations may decrease or even increase them. Also, it is certain that not all the species included have originated in the “isolated “areas; some of the most distinct have probably been much more widely spread, and are “relics “merely.
The continuity of distribution of species of the New Zealand flora varies from those with a fairly continuous distribution to those which occur in only a few localities far distant from one another. Notable examples of extreme discontinuity are: Danthonia antarctica Hook. f., common in
Auckland and Campbell Islands, but confined elsewhere to a few rocky points and small islands in the far north of the North Island; Urtica australis Hook. f., common in Chatham, Antipodes, and Auckland Islands, but in New Zealand proper occurring only on Dog and Centre Islands, Foveaux Strait; Drosera pygmaea D.C., only recorded from near Kaitaia in the extreme north and the Bluff Hill in the extreme south; Pittosporum obcordatum Raoul, occurs sparingly near Kaitaia, and Akaroa, Banks Peninsula; Plagianthus cymosus T. Kirk, only recorded from Dunedin, Lyttelton, some of the Marlborough Sounds, and Kaitaia; Suttonia chathamica Mez, common in the Chatham Islands, and found in two localities in Stewart Island; Lepyrodia Traversii F. Muell., common in Chatham Island, and found in certain bogs of the Waikato and at one locality near Kaitaia; Styphelia Richei Labill., common in Chatham Island, and found elsewhere only near the North Cape; Melicytus macrophyllus A. Cunn., common in certain Auckland forests, but absent elsewhere, except one locality near Dunedin Other examples of discontinuous distribution, though more connected than the above, include Elaeocharis sphacelata R. Br., Dracophyllum latifolium A. Cunn., Clematis afoliata Buch., Quintinia acutifolia T. Kirk, Celmisia Traversii Hook. f., Pseudopanax ferox T. Kirk, Carmichaelia gracilis J. B. Armstg., Coprosma rubra Petrie, Veronica speciosa R. Cunn., &c. Were there merely one or two cases the discontinuous distribution might be attributed to chance, but as there are numerous cases, and as these gradually merge into examples of greater and greater continuity, it is probable that the species in most cases were at one time more widely spread, and that in the extreme cases as above we are face to face with the phenomenon of a species naturally on the verge of extinction.