In the present imperfect knowledge of the laws which regulate the distribution of species, any authenticated records of the introduction of exotic species into new countries, and their subsequent diffusion, must of necessity possess high value, and be alike calculated to throw light on the obscure past, and to prevent the adoption of error in the future. the opportunities afforded by modern colonization, or watching the introduction of foreign species, and noting their diffusion in new countries, by agencies uncontrolled by man, have been, to a great extent, neglected. In truth, it is far easier to recognize results, than to watch the processes by which the results are brought about; a few years sometimes suffice to show us the displacement of the greater portion of the vegetation of certain localities, although the process itself has been so gradual as almost to have escaped notice; yet when, as in these islands where settlement is in its infancy, we find much of the original vegetation displaced by non-indigenous plants, established about the early mission stations, and seats of commerce, about mines, timber stations, and cattle runs, in short, wherever the immigrant has fixed his temporary or permanent home; we are insensibly led to entertain wider views of the changes which the floras of countries of ancient civilization must have undergone by successive immigrations of plants from other countries. In this light we may glance for a moment at the flora of the British Islands, the flowering section of which is supposed by botanists to consist of naturalized plants to the extent of from one-seventh to one-fourth, or even a higher proportion. If we look back to the time of Phoenician commerce and settlement in the western part of the island, we can readily conceive of plants, from the countries on the Euxine and the Mediterranean, having been accidentally introduced and amalgamated with the indigenous flora. In later times we have no difficulty in extending the idea to those countries which sent to Britain successive hordes of invaders; and in the present day we can point to plants and animals, alike of accidental introduction in the footsteps of commerce, which have become widely naturalized; take for examples, Impatiens fulva, Elodea alsinastrum, and the fluviatile mollusk Dreissena plymorpha.
Now although the robust growth of the modern civilization has buried many traces of the less vigorous ancient forms, it would seem not utterly impossible that a more careful and comparative examination than has yet been made of the floras of the countries, from which Britain received her ancient settlers and invaders, might lead to the removal of much of the uncertainty and doubt that exist as to the indigenous or exotic origin of so large a proportion of her flora; and might also show, to some extent, what those countries had received from Britain, and from each other. To apply this in
the case of New Zealand: it is but a century since the islands were discovered by Cook; less than sixty years since the early visits of whalers, and the establishment of the first mission stations; and not half that period has elapsed since settlement was commenced in a systematic manner, yet already the number of naturalized plants,—that is to say, of non-indigenous plants propagating their species, and becoming diffused without the intentional agency of man, or even in opposition thereto, in the Province of Auckland alone,—is equivalent to fully thirty per cent. of the entire number of flowering plants found within the limits of the Colony; a proportion equalling, as we have already seen, that which exists in the British Islands, with a commerce dating from a period anterior to the Christian era. Some of these introductions have largely displaced the original vegetation in many localities, from the North Cape to the Bluff; from the sea level to the highest spots on the hills trodden by the miner or shepherd; while others are confined to a limited area, and apparently exercise no direct influence on the original flora.
A reliable account of the present state of even a few species is a contribution of no small value, tending to prevent the uncertainty and confusion with regard to the geographic origin of a large portion of the flora, which we have seen to prevail so largely in countries of old commerce and civilization, affording a starting point for measuring the rate of diffusion, and noting the power of displacement of, or amalgamation with, the original flora; and in this and other points preparing important material for unlocking the histories of past immigrations in other countries.
The object of this paper is simply to place upon record the present state of the diffusion of naturalized plants in this province, as fully as the available material will allow, with a due regard to conciseness. In those cases where the species under notice is known to occur in other parts of the colony, the facts will be mentioned, but unhappily, these are far too few to admit of this sketch being considered anything more than a sketch of the naturalized plants of the Province of Auckland.
For the facts recorded in this paper, the writer is personally responsible, except when otherwise stated; the only published accounts available, are a list of about sixty species given in “Flora Novæ Zelandiæ,” Vol. ii.; a list of about one hundred and seventy species in the “Handbook of the New Zealand Flora,”—the additions comprised in which, were largely contributed by the present writer; and lists of the naturalized plants of the Great Barrier Island, and other localities, prepared by him, and published in the “Transactions of the New Zealand Institute,” Vol. i.
Many important bearings of this subject will, it is hoped, afford material for future study. The increased diffusion of certain of the indigenous species by external agencies, only called into operation since the settlement of the colony; the possible introduction of a few additions to the original flora, by the Maori race; the displacement of a portion of the original species; the spontaneous amalgamation of introduced and native species for the benefit of man; the relative statistical importance of the naturalized species to each other, and to the indigenous flora; the influence of climatal and geognostic conditions in facilitating or retarding distribution, and in developing aberrations from the original type, are attractive subjects of vast importance to the phyto-geographical student, and at the present time could probably be worked out more clearly and with greater precision for this colony than for any other country whose flora is equally well determined, owing to the small admixture of error with the facts upon which the student must base his conclusions.
The following plan has been adopted for expressing the known facts for each species, in a concise manner, and admits of ready adaptation for other districts.