Art. XXV.—On the Occurrence of Littoral Plants in the Waikato District.
[Read before the Auckland Institute, June 13, 1870.]
The frequent occurrence of several species of maritime plants in the Waikato District, far beyond the present range of tidal waters, appears to call for special remark from its important geological bearings. Dr. Hochstetter was, I believe, the first to advance the theory, “that the whole Middle Waikato basin was but recently a shallow arm of the sea or a far extending estuary.” The accuracy of this opinion has however been impugned; it may therefore be advisable to recapitulate the maritime plants observed in and about the river and adjacent lakes and marshes.
Tetragonia expansa,—chiefly as a weed in native cultivations.
Apium filiforme,—woods by the Opuatia.
Selliera radicans, Cav.,—Waikare Lake. Has been found by the “Lower Waitaki River, Otago, apparently far from the sea.”
Chenopodium glaucum, L., var. ambiguum,—on the shores of Whangape Lake.
Ruppia maritima, L.,—in Whangape, Waikare, and Waihi Lakes.
Leptocarpus simplex, A. Rich, — Waikare Lake. This occurs in a solitary locality in the North, a short distance only from the present reach of tidal water, and in small quantity.
Scirpus maritimus, L.,—from Waikato Heads to a few miles above Hamilton; abundant in all the lakes and marshes; also in the Waipa.
Zoysia pungens, Willd.,—Cambridge, abundant.
Unless specially mentioned, I am not aware of the occurrence of any of the foregoing beyond the reach of tidal waters.
No mention is made in the foregoing list of two or three littoral plants of doubtful identification, or of a few species, such as Potamogeton pectinatus and Zannichellia palustris, which are found indifferently in fresh or brackish water in Europe, but are of extreme rarity in New Zealand, and occur in the Waikato in company with known littoral species; and it should be remembered, that the advanced period of the season at which these observations were made was unfavourable for field work, as in their decaying state several of the smaller growing kinds were doubtless overlooked in some of the localities visited, and other species may have escaped notice altogether.
It is readily admitted that littoral plants may occasionally be found in inland situations from accidental causes, but in the present case the number of species, and the wide area over which they collectively extend, afford forcible proof that the cause of their growth must be found in the district having been formerly a shallow estuary, probably connected with the Frith of the Thames. Bearing in mind, that with each rising of the river the current at first runs swiftly into the lakes of Lower Waikato from the river, instead of from the lakes into the river, a ready explanation is afforded of the way in which these littoral plants have become established there. It is difficult to imagine that a plant of salt marshes, as Scirpus maritimus, could be carried from the mouth of the river, against a rapid current, for a distance of one hundred miles along its banks, and diffused over the fresh water lakes and swamps of a large extent of country besides. It is easy of comprehension how, if introduced from the Frith of the Thames, it would become established in the marshes, etc., on the retirement of the river to its present bed, and carried downwards until it again met the tidal water on the western coast.
There can be little doubt that a careful examination of the country between the Frith of the Thames and Middle Waikato, would result in the collection of additional evidence on this interesting subject.