Island Life; Or, The Phenomena and Causes of Insular Faunas and Floras

by Alfred Russel Wallace

CHAPTER XXII

THE FLORA OF NEW ZEALAND: ITS AFFINITIES AND PROBABLE ORIGIN

Relations of the New Zealand Flora to that of Australia—General Features of the Australian Flora—The Floras of South-eastern and South-western Australia—Geological Explanation of the Differences of these two Floras—The Origin of the Australian Element in the New Zealand Flora—Tropical Character of the New Zealand Flora Explained—Species Common to New Zealand and Australia mostly Temperate Forms—Why Easily Dispersed Plants have often Restricted Ranges—Summary and Conclusion on the New Zealand Flora.

Although plants have means of dispersal far exceeding those possessed by animals, yet as a matter of fact comparatively few species are carried for very great distances, and the flora of a country taken as a whole usually affords trustworthy indications of its past history. Plants, too, are more numerous in species than the higher animals, and are almost always better known; their affinities have been more systematically studied; and it may be safely affirmed that no explanation of the origin of the fauna of a country can be sound, which does not also explain, or at least harmonise with, the distribution and relations of its flora. The distribution of the two may be very different, but both should be explicable by the same series of geographical changes.

The relations of the flora of New Zealand to that of Australia have long formed an insoluble enigma for

botanists. Sir Joseph Hooker, in his most instructive and masterly essay on the flora of Australia, says:—"Under whatever aspect I regard the flora of Australia and of New Zealand, I find all attempts to theorise on the possible causes of their community of feature frustrated by anomalies in distribution, such as I believe no two other similarly situated countries in the globe present. Everywhere else I recognise a parallelism or harmony in the main common features of contiguous floras, which conveys the impression of their generic affinity, at least, being affected by migration from centres of dispersion in one of them, or in some adjacent country. In this case it is widely different. Regarding the question from the Australian point of view, it is impossible in the present state of science to reconcile the fact of Acacia, Eucalyptus, Casuarina, Callitris, &c., being absent in New Zealand, with any theory of transoceanic migration that may be adopted to explain the presence of other Australian plants in New Zealand; and it is very difficult to conceive of a time or of conditions that could explain these anomalies, except by going back to epochs when the prevalent botanical as well as geographical features of each were widely different from what they are now. On the other hand, if I regard the question from the New Zealand point of view, I find such broad features of resemblance, and so many connecting links that afford irresistible evidence of a close botanical connection, that I cannot abandon the conviction that these great differences will present the least difficulties to whatever theory may explain the whole case." I will now state, as briefly as possible, what are the facts above referred to as being of so anomalous a character, and there is little difficulty in doing so, as we have them fully set forth, with admirable clearness, in the essay above alluded to, and in the same writer's Introduction to the Flora of New Zealand, only requiring some slight modifications, owing to the later discoveries which are given in the Handbook of the New Zealand Flora.

Confining ourselves always to flowering plants, we find that the flora of New Zealand is a very poor one, considering the extent of surface, and the favourable conditions of

soil and climate. It consists of 1,085 species (our own islands possessing about 1,500), but a very large proportion of these are peculiar, there being no less than 800 endemic species, and thirty-two endemic genera.

Out of the 285 species not peculiar to New Zealand, no less than 215 are Australian, but a considerable number of these are also Antarctic, South American, or European; so that there are only about 100 species absolutely confined to New Zealand and Australia, and, what is important as indicating a somewhat recent immigration, only some half-dozen of these belong to genera which are peculiar to the two countries, and hardly any to the larger and more important Australian genera. Many, too, are rare species in both countries and are often alpines.

Far more important are the relations of the genera and families of the two countries. All the Natural Orders of New Zealand are found in Australia except three—Coriariæ, a widely-scattered group found in South Europe, the Himalayas, and the Andes; Escallonieæ, a widely distributed group; and Chloranthaceæ, found in Tropical Asia, Japan, Polynesia, and South America. Out of a total of 310 New Zealand genera, no less than 248 are Australian, and sixty of these are almost peculiar to the two countries, only thirty-two however being absolutely confined to them.[^[179]] In the three large orders—Compositæ, Orchideæ, and Gramineæ, the genera are almost identical in the two countries, while the species—in the two former especially—are mostly distinct.