Introduction

When Cockayne (1928: 408) suggested that ‘New Zealand possessed a flora, part of which had originated on her own soil,’ he included genera with the majority of their species endemic to New Zealand but with one or more species occurring elsewhere, in Australia, South America, or on Pacific islands. He assumed this element to be of New Zealand origin and to be ancient (by which he meant Tertiary), called it ‘Paleozelandic’ and implied that some of its members had migrated from their place of origin in New Zealand to Australia, Malaya or South America.

It cannot always be concluded that a genus originated in the area that now supports the greatest number of species; nor should we include taxa (like Phyllocladus) that now apparently occupy only a part of their former range (Couper, 1960a). There remain, however, a number of taxa of animals as well as of plants, for which a New Zealand origin seems extremely probable, although this conclusion can seldom be tested by paleontological evidence.

Colonisation of Offshore Islands

The presence of characteristic New Zealand organisms in the adjacent islands that rise from the system of submarine rises to the north-west, east and south has been taken for granted, without much consideration of its implications.

Judged by recent paleogeographic studies (Fleming, 1960; Stevens, 1974) most of New Zealand's outlying islands have not been connected with the mainland during the Tertiary. Even those over continental crust such as the Chatham, Auckland and Campbell islands have not necessarily had a continuous history as land but have mainly been established by Tertiary volcanism on up-domed portions of the sea floor. Moreover, islands in the sub-antarctic zone suffered severe cold climates (if not glaciation) during the Quaternary ice ages, so that many of their inhabitants, both plant and animal, are young colonists from across the seas.

The youth of many colonists on offshore islands is shown by their close relationship to parent stocks in New Zealand. Thus the New Zealand Nestor parrots formerly living in Norfolk and Chatham page 31

Fig. 1: Occurrence of endemic genera of New Zealand birds and plants at Norfolk, Kermadec, Chatham and Auckland islands.

islands, the Prosthemadera honeyeaters at the Kermadec, Chatham and Auckland islands, and Hemiphaga pigeons at Norfolk and Chatham islands range from populations identical with the mainland page 32

Fig. 2: Norfolk, Kermadec and Chatham islands were colonised by cicadas of the endemic New Zealand genus Kikihia whereas Lord Howe Island was colonised from Australia and the tropical Pacific islands from the Oriental Region via New Guinea.

forms to subspecies and in one case (Nestor productus) a moderately well-differentiated species (data from Matthews, 1931). The Auckland Island Prosthemadera must be a post-glacial colonist of the last 10,000 years and there is little reason to assume much greater antiquity for the others. The presence of the New Zealand monocotyledon Phormium tenax (Agavaceae), otherwise generically endemic, at Norfolk, the Chatham and Auckland islands and of the palm Rhopalo-stylis at Norfolk and the Kermadec islands (Moore and Edgar, 1970) is almost an exact parallel to the three bird distributions just cited (Fig. 1), but for these plants there is some fossil evidence (Couper, 1960b). An extinct Phormium (judged by fossil pollen) was in New Zealand during the early Tertiary, prior to the evolution of the modern species (Couper, 1960b), one of which (Phormium tenax) must have colonised the islands at quite a late Cenozoic date (post-glacially in the Auckland Islands). Rhopalostylis also has a pollen record back to Eocene, but its three allopatric species may be of greater age than the insular Phormium population.

Endemic genera of cicadas evolved in New Zealand, apparently from Australian colonist stocks, probably during the Tertiary, and their adaptive radiation, to occupy stations from coastal sand-dune to mountain fellfield, from rain forest to bare river-bed, was conditioned by the diversification of New Zealand environments during the Quaternary. Members of two species groups in the genus Kikihia Dugdale, showing a speciation pattern no older than Quaternary, have colonised islands, the muta group occupying Norfolk Island and the Chathams and a characteristic green cicada (K. cutora) reaching the Kermadec Islands (Fleming, 1973). Their New Zealand affinities stand in sharp contrast with those of Lord Howe Island cicadas which were unambiguously derived from Australia, and those of Fiji and Samoa which were derived from the Oriental region (Fig. 2).

The random nature of such trans-oceanic colonisations or of their success is emphasised by the occurrence of a single species of broom, Carmichaelia (otherwise endemic to New Zealand with 38 species there in 8 subgenera) on Lord Howe Island and their absence from closer islands (Fig. 3).

Polynesian Islands

Collospermum (Liliacea), with two New Zealand species, has single species in montane Fiji and Samoa, generally considered derivative (Fig. 3), but we may here see only relict parts of its former total range and its evolution in New Zealand may be judged uncertain (cf. Skottsberg, 1937).

The four New Zealand species of Fuchsia ^* are segregated in the section Skinnera and thus isolated from the South American members of the genus. Their fossil pollen record (Couper, 1960b) indicates a Tertiary history in New Zealand. There is thus strong presumptive evidence of New Zealand origin for a close relative of one New Zealand species that lives on the mountains of Tahiti, and for transoceanic transport to these oceanic volcanic islands, presumably by means of its succulent fruit (Fig. 3).

The genus Melicytus (Violacea) is endemic to New Zealand (4 species) except for one species that ranges to Norfolk Island, Fiji, Tonga and the Kermadec Islands (Fig. 3), lack of speciation in these peripheral populations strongly suggesting a recent date of colonisation. Its berry is eaten by birds.

That birds have crossed the sea from New Zealand to some of the Pacific islands so far named is evidenced by the distribution of the parakeet genus Cyanorhamphus (see Peters, 1937) which is centred on New Zealand (with 3 species) but is (or was formerly) represented on all offshore islands, some of which Antipodes Islands, Auckland Islands, Chatham Islands) have been successfully colonised twice (Fig. 4) so that they support 2 species. page 34

Fig. 3: Distribution of otherwise endemic New Zealand plants on islands in the south-west Pacific.

page 35

Fig. 4: Distribution of parakeets of the New Zealand genus Cyanorhamphus in the south-west Pacific from New Caledonia and Tahiti south to Macquarrie Island and of the plant genus Hebe, of which two New Zealand species range to Fuegia and one of them to the Falkland Islands.

The most persistent colonist, Cyanorhamphus novaezealandiae, had reached New Caledonia, Norfolk, Lord Howe, Kermadec, Chatham, Antipodies, Auckland and Macquarie islands so recently that the majority of insular populations were weak subspecies. Related species, somewhat more distinct and thus probably older, lived on two of the Society Islands when Europeans first visited them. The dates of page 36 colonisation must remain speculative, but the sub-antarctic forms are probably post-glacial and using the degree of difference developed in that time as a yardstick the Tahiti and Raiatea species are unlikely to be older than Pliocene.

Fuegia

Even more distant regions were colonised by Hebe, which has its headquarters in New Zealand (79 species) with a few species in Tasmania, south-east Australia and New Guinea. Two New Zealand species range to southern South America, and one extends further, to the Falkland Islands. The New Zealand species show every indication of active evolution, high variability, and of incomplete speciation, so that the occurrence of two indistinguishable derivative populations in South America implies a geologically recent date of colonisation, down the West Wind Drift, probably caked to the feet or feathers of seabirds (Falla, 1960; Godley, 1967).

The beetle genera Kenodactylus Broun and Oopterus Guerin have reached Patagonia and the latter has also reached Falkland, Kuerguelen and South Georgia islands as the result of transoceanic migration of New Zealand stock from which they are derived (Johns, 1974). They thus provide a zoological parallel to the two subspecies of Hebe that have crossed the Pacific from New Zealand.

Westward to Australia?

Whereas many New Zealand organisms were derived from Australia by eastward movements across the Tasman Sea, plant genera like Aciphylla, Anistome, Celmisia and Dracophyllum which are centred on New Zealand (with 20 to 58 species), but have one or a few Australian species, suggest a modest return flow. Among marine shallow-water molluscs there is an occasional example of a genus appearing in Australia after a well-documented earlier history in New Zealand.

In our own time, several species of endemic New Zealand shallow-shelf mollusca have appeared abundantly in Tasmania (Greenhill, 1965), perhaps dispersed with the assistance of merchant shipping. Dominantly westerly winds and eastward sea-surface currents are now opposed to westward transport of drifting organisms, both marine and terrestrial, but such movements may have been easier in the past if the South Equatorial Current lay further to the south during periods of Tertiary warmth than it does today.

Conclusions

Cockayne's opinion that a New Zealand element can be recognised in the biota of other Pacific countries is supported by the present incomplete review which includes zoological and fossil evidence not available to him. On available evidence, the geological age of colonisations by such New Zealand elements seems to have been late Cenozoic, Quaternary, or even post-glacial. The term ‘Paleozelandic’, however, is not appropriate for a group of taxa of variable Cenozoic age in New Zealand, since it implies that they are old elements (if not the oldest) in the New Zealand biota. That the colonisations discussed took place across the sea is consistently supported by their random pattern, by their apparently late date, and by the geological history of recipient islands.

References

Allan, H. H., 1961: Flora of Nex Zealand, Vol. I. Government Printer, Wellington.

Cockayne, L., 1928: The Vegetation of New Zealand (2nd ed.), Vol. XIV, in Engler and Drude's Die Vegetation der Erde. W. Engelmann, Leipzig.

Couper, R. A., 1960a: Southern Hemisphere Mesozoic and Tertiary Podocarpaceae and Fagaceae and their palaeogeographic significance. Proceedings of the Royal Society, B 152 (949): 491-500.

——, 1960b: New Zealand Mesozoic and Cainozoic Plant Microfossils. Paleontological Bulletin of the New Zealand Geological Survey 32, 87 pp.

Falla, R. A., 1960: Oceanic birds as dispersal agents. Proceedings of the Royal Society B 152: 655-659.

Fleming, C. A., 1960: New Zealand Biogeography. A paleontologist's approach. Tuatara 10 (2): 53-108.

——, 1973: The Kermadec Islands cicada and its relatives (Hemiptera: Homoptera). N.Z. Journal of Science 16 (2): 315-332.

Godley, E. J., 1967: Widely distributed species, land-bridges and continental drift. Nature 214: 74-75.

Greenhill, J. F., 1965: New Records of Marine Mollusca from Tasmania. Papers and Proceedings of the Royal Society of Tasmania 99: 67-69.

Johns, P. M., 1974: Arthropoda of the Subantarctic Islands of New Zealand (1). Coleoptera: Carabidae. Southern New Zealand, Patagonian and Falkland Islands insular Carabidae. Journal of the Royal Society of New Zealand 4 (3): 283-302.

Matthews, G., 1931: A list of the birds of Australasia. 562 pp. London.

Moore, L. B., and Edgar, E., 1970: Flora of New Zealand, Vol. II. Government Printer, Wellington.

Peters, J. L., 1937. Checklist of the Birds of the World, Vol. II. Harvard University Press.

Skottsberg, C., 1937: Recent researches in Astelia B. and S. Transactions of the Royal Society of New Zealand 67: 218-226.

Stevens, G. R., 1974: Rugged Landscape. A. H. and A. W. Reed, Wellington.