Art. XLIII.—On the Specific Characters of Dicksonia antaretica, Br. and Dicksonia lanata, Col.
[Read before the Auckland Institute, 14th October, 1872.]
The characters presented by Dicksonia antarctica and D. lanata in these islands are so remarkably constant and so easily recognized, owing to the absence of intermediate forms, that it seems desirable to inquire if their union, under the name of Dicksonia antarctica, can be maintained. I must confess at the outset that it is with the greatest diffidence I venture to dissent from the opinion of so high an authority as the late Sir William Hooker, but after a careful examination of both forms in a recent condition, and in many localities, it appears to me that a student unacquainted with either would fail
to identify the form generally known to New Zealand botanists as “lanata” by the aid of the diagnosis of “antarctica” given in “Synopsis filicum,” although the former is quoted as a synonym.
Dicksonia antarctica, the wekiponga of the Maoris, is a fine arborescent fern, in these islands attaining the height of from 10 to 20 feet or more, with the trunk clothed with a dense covering of fibrous, matted rootlets so that it is sometimes 18 inches in diameter (in Australia it attains the height of 40 ft., with a diameter of 4 ft.), presenting a peculiar, massive, and columnar appearance, by which it is at once recognized. Fronds spreading, lanceolate, 4 to 8 ft. in length, and from 8 to 18 inches in width; stipes extremely short, the dead fronds being persistent and completely shrouding the upper part of the stem, coriaceous, and of a peculiarly harsh, thin texture, green beneath; primary divisions 5 to 9 inches in length, narrowed into long points, segments acutely toothed, oblong. Barren fronds similar to the fertile.
At Ohinemutu a small group of specimens of this form may be seen growing in an exposed rocky situation on the banks of the lake. Yet notwithstanding their depauperated condition the distinctive characters are as strongly marked as in the largest specimens on the adjacent hills. There is not the slightest approach to the appearance of D. lanata when growing under similar conditions.
In D. lanata the caudex is usually wanting, and is never more than from 4 to 5 ft. in height; it never produces matted rootlets, except as in all tree-ferns at the very base, so that the attached portions of the old stipes are visible from the root to the apex; fronds arched, ascending, 1 to 5 ft. in length, broadly lanceolate or elliptic, 1 to 2 ½ feet broad, abruptly acuminate; stipes at least half the length of the frond; lower primary divisions oblongdeltoid, upper oblong, abruptly acuminate, not narrowed into long points, very coriaceous; segments broadly oblong, obtusely toothed; the base of the stipe clothed with long jointed hairs, much more luxuriant than in D. antarctica; rachis glabrous or sparingly pubescent; sori larger and more prominent than in D. antarctica. Barren fronds, with the pinnæ deltoid; segments coriaceous, lobulate or pinnatifid, obtusely toothed, whitish below.
From the preceding brief statement it will, I think, be readily granted that the difference between the two forms is too great to allow of their being lumped together without at least some mention of their prominent characteristics, more especially as their distribution in these islands exhibits marke d peculiarities.
D antarctica is found from Tauranga to Otago, and is most abundant in the for ests of the interior, ascending to about 3,000 feet.
D anata is found from Mongonui to Nelson, and does not occur at above 2,000 ét.
It is especially to be remarked that arborescent specimens of D. lanata become rare as the plant recedes from the north, until at Taupo, as was long since pointed out by Colenso (the discoverer of both species in the colony) it covers the ground like Pteris. At Whangarei, Kaipara, and other localities north of the Auckland Isthmus, stemless specimens are extremely rare,—arborescent specimens are abundant. D. lanata is also far more local within its area than D. antarctica.
D. lanata is endemic in these islands, while D. antarctica is found in East Australia, Tasmania, New Caledonia, and New Zealand.
Colenso states that the Maoris of the interior formerly used boards cut from the fibrous part of the stem of D. antarctica in the construction of their provision stores, the tough wiry fibres affording almost complete immunity from the attacks of rats.