Art. XLI.—On the Nativity in New Zealand of Polygonum aviculare, L.
[Read before the Auckland Institute, 26th June, 1871.]
At page 336 of the Transactions of the New Zealand Institute for 1870, Mr. Travers has given prominence to a difference of opinion that exists between us on the question of the nativity of Polygonum aviculare, L., in the colony. As his conclusion that it is of exotic origin does not appear to me to be supported by the facts of the case, I purpose briefly stating the conditions under which the plant occurs, and placing on record one or two interesting points connected with its distribution.
The only alleged or inferential reason adduced by Mr. Travers in support of his view is comprised in the following statement:—“The natives, moreover, who suffer much inconvenience from its spread, call it a ‘pakeha’ or foreigner,”
I must point out that this statement is essentially misleading, as it is true only of a portion of the South Island, and does not in any way apply to the North Island, or to the northern portion of the South Island.
In the North Island this plant exhibits exactly similar characteristics of abundance and luxuriance to those which it manifests in the British Islands. It is commonly found by road sides and on waste land, on cultivated land, and on grassy places in the forest. I have not observed it at a greater altitude than 1,800 or 1,900 feet, but there can be little doubt that it will be found at a greater height on the central ranges. I never met with an instance of its occurring in native cultivations to such an extent as to cause “much inconvenience,” and the same remark applies to its occurrence in the more extended cultivations of the settlers. I may add that around the chief seats of settlement in the North Island — Auckland, Napier, New Plymouth, and Wellington—also about Nelson in the South Island, it occurs under the same relative conditions as to extent and luxuriance that have just been described. It nowhere obtrudes itself upon the attention of a new-comer from occurring in greater abundance than in ordinary localities in the British Islands, and I am satisfied, from close observation during the past eight or nine years, that it has not increased in a greater ratio than might fairly be expected from the increase of favourable habitats afforded by the spread of agricultural operations. This view of the case is supported by the direct testimony of old settlers and missionaries; our president states that the plant has, to his personal knowledge, held the same relative position-for the past thirty years that it now occupies.
In the middle and southern part of the South Island the Knot-grass has increased excessively: at present, however, it does not appear whether the typical form of the plant participates in this increase or not. So far as the evidence in my possession is precise on the point, it refers only to the var. Dryandri. In the “Natural History Review” for October, 1864, Mr. Travers writes:—“This plant (Polygonum aviculare) grows with extraordinary vigour all over the country (Canterbury), where the soil has been at all disturbed, completely replacing the native plants. Its roots often penetrate to the depth of three and four feet,”—and in an earlier number of the same periodical it was stated on the authority of Mr. Travers that plants “spread over an area four to five feet in diameter.” In the “Handbook of the New Zealand Flora,” the typical form is stated to have been collected by M. Raoul on Banks Peninsula, thirty years ago, and the var. Dryandri at Port Cooper, by Dr. Lyall, eight or ten years later. I possess a Christchurch specimen of the variety labelled “P. aviculare,” collected by Mr. Armstrong, who remarks that it is found “in great abundance and spreading with great rapidity.” In the “Handbook” it is also stated that the variety Dryandri “covers acres of
ground by road-sides in Otago.” It is certainly desirable to ascertain whether the typical form exhibits the same power of rapid increase as the variety. In the North Island the variety is recorded from the East Coast on Mr. Colenso's authority, but I cannot learn that it exhibits the strongly marked facility of propagating itself which it manifests in the south. The only locality in which I have collected it is on the Great Barrier Island, where, in 1867, it was rather plentiful on a small patch of ground at Puriri Bay, but was not observed elsewhere; strange to say on searching the locality in March last, I failed to find a single specimen! while the typical form appeared to have neither increased nor diminished since my previous visit.
The peculiar eastern distribution of the variety Dryandri is certainly singular, and taken in conjunction with its excessive abundance and rapid increase in the south may possibly justify suspicion as to the exotic origin of this particular form; but, unless supported by more direct evidence, this is quite inadequate to warrant a positive conclusion on the subject, especially in the absence of any similar increase in the north, with its more advantageous climatal conditions. In no case can this affect the question of the introduction of the typical form; even should it be proved that this exhibits in the south the rapid diffusion which is so strongly marked in the variety, the fact will still remain that during actual observation, extending over thirty years, the peculiarity has not been evidenced in at least two-thirds of the colony.
But arguments in favour of exotic origin, based, as in the present case, solely upon the abundance and rapid increase of a plant in certain localities, cannot in any case be considered conclusive in the face of the remarkable increase exhibited by plants whose nativity is unquestioned. Mr. Travers himself has placed a marked instance on record: I select it chiefly from its occurring in the same district as the subject of this paper. In the article from which I have already quoted, Mr. Travers states that “Azolla rubra is rapidly increasing, and utterly impedes the progress of draining in the lower and more level tracts of the country.” A startling phenomenon, as compared with the conditions under which this plant occurs in the north; yet, I imagine, no one would think of suggesting the great abundance and rapid increase of Azolla, in the province of Canterbury, as evidence of its exotic origin in that province, much less in the colony at large.
It is singular that Mr. Travers should adduce the opinion of the natives as evidence of the exotic origin of the Knot-grass, when he has seen fit to reject it with regard to the introduction of the Flesh-fly, of which he has given so interesting an account in the last volume of the Transactions. My own experience has led me to the conclusion that native evidence on questions of this kind is usually worthless, and it is commonly stated by the old residents and missionaries that the Maoris of the present day are greatly inferior to those of
one or two generations back as observers of natural phenomena. Any person who may take the trouble to inquire the names of even common plants from the Maoris, will quickly find the same name applied to very different plants— no two individuals agreeing in their application. In the Waikato I have heard the common Ngaio (Myoporum lætum) called a “pakeha” tree.
The causes of the rapid diffusion of plants in certain localities are often obscure, but in all cases are worthy the attention of observers resident in the localities where their operations are exhibited. Many curious instances of the local diffusion of rare plants will be readily called to mind by the student of European floras—the viatical plants especially, to which the subject of this paper belongs, furnish an assemblage of remarkable phenomena of this kind.