Art. XLVII.—Notes on Dactylanthus taylori, Hook. f.
[Read before the Wellington Philosophical Society, 25th September 1895.]
The remarkable monotypic genus Dactylanthus constitutes the fourth tribe of Balanophoreæ, an order of root-parasites most of which have a very local distribution. Dactylanthus, the “pua-reinga” of the Maoris, was originally discovered about 1857 by the Rev. Richard Taylor, growing on the roots
of Pittosporum, Fagus, and other trees near the head of the Whanganui River, at an estimated altitude of 4,000ft. Although the plant grows over a wide area it is remarkably local, so that it is desirable to record the localities in which it has been observed. After its original discovery it does not appear to have been noticed by any collector until April, 1869, when I had the good fortune to discover it, at an altitude of 1,800ft. or 1,900ft., on the Thames Goldfield, where it was parasitic on the roots of Schefflera digitata and Coprosma grandifolia; but, owing to the advanced period of the summer, the specimens were so much decayed that only the rhizomes were in a fit state for removal: several of these were deposited in the Colonial Museum.* It was decidedly rare, and was limited to a very small area. Although I paid several visits to the habitat in subsequent years, the complete destruction of the arboreal vegetation by mining operations appeared to have killed the parasite; but I believe it has been recently collected by Mr. Cheeseman, either in the habitat where it was first observed by me or some other in its near vicinity. It was next observed by Mr. J. P. Marshall on the banks of the Mohanga River, Rangitikei, and he kindly presented me with a male specimen in 1878. In 1887 it was collected by Mr. W. H. Skinner in the Taranaki District, but I am ignorant of the exact locality, although Mr. Skinner generously forwarded his specimen for my herbarium. It is the only female specimen that I have seen; the fruits are fully formed, but not ripe. Two small specimens were very kindly given me at a later date by Mr. H. C. Field, who found them in the Whanganui district, but did not state the precise locality. More recently it has been discovered in two localities by Mr. A. Hamilton—at Tarawera, between Taupo and Napier, and at Nuhaka, near the Mahia Peninsula. I am indebted to his goodness for a specimen from the latter habitat. It has also been found in considerable quantity in the forest district between Clyde and Waikaremoana, but the discoverer's name is unknown to me. Lastly, it has recently been found by Mr. H. Hill in the East Cape district, where it evidently grows in great luxuriance, judging from the fine specimen which he has liberally presented to the Colonial Museum; it measures fully 8in. across, and is by far the largest that has come under my notice.
Unhappily, most of the specimens at present obtained are in very poor condition, and enable us to add but little to the excellent description drawn by Sir Joseph Hooker from the material collected by the Rev. R. Taylor. The following notes are written in the hope that they may prove of sufficient
[Footnote] * See Trans. N.Z. Inst., ii. (1869), p. 94.
interest to draw the attention of surveyors, explorers, and settlers in forest districts to one of the most remarkable plants in the flora.
The large rhizome by which it is attached to the roots of its host is usually subterranean, very woody, rounded or amorphous, entire or deeply lobed, and forms a kind of boss, covered on the surface with rounded papillæ, each of which marks the point at which a flowering-stem, was given off. The rhizomes vary greatly in size; some might be completely hidden under a penny-piece, while others are fully 8in. in diameter and 4in. or 5in. thick. When growing on a declivity, roots of the host-plant, from which the soil has been washed away, may be found with the rhizome of the parasite fully exposed, when the position of the flowering-stems is easily made out; but usually the rhizome is buried in the humus amongst which it grows, and only the upper part of the flowering-stems rises above the soil to a greater or less extent.
The flowering-stems are diœcious, from 2in. to 5in. long, somewhat club-shaped, and clothed with brown ovate or oblong imbricating scales, which are evidently fleshy when first developed, but at length become so brittle that they crumble into minute fragments at the slightest touch. The flowers are developed on very short spadices, lin. to 1 ½in. in length at the apex of the stem, and are mostly hidden by the apical scales; the males, which I have not seen, are covered with crowded anthers, and the females with sessile ovaries in great profusion. The ripe fruit is about the size of a radish-seed, and contains a minute undivided embryo, imbedded in granular endosperm. Unhappily, nothing is at present known of the process of germination and development.
Although the dull-brown colour of the flowering-stems renders the portion that appears above ground very inconspicuous, the flowers emit a strong perfume. In a letter to Sir James Hector, Mr. Hill states that he was enabled to discover the plant solely through the “delicious daphne-like fragrance which it emitted,” his attention being first attracted by the perfume.
The large area over which it has already been observed, extending from the Hauraki Gulf to Taranaki and Rangitikei, warrants the idea that a careful search would be rewarded by its discovery in localities where its occurrence has not hitherto been suspected. Any explorer or settler who would communicate a supply of good specimens would render a great service to botanists at large, although there is nothing in the material that has come under my notice to support the idea of there being more than a single species.
Further Notes, read 16th October, 1895.
The following extract of a letter from Mr. A. Hamilton, informing me of the discovery of Dactylanthus at Tarawera, will be read with interest. It is dated 28th March, 1883 :—
“Some time ago, when I went to Lake Waikaremoana, you were kind enough to send me a list of plants which I should endeavour to find, and made particular mention of Dactylanthus taylori. Although at that time I was not fortunate enough to see or hear of any specimens, I have been on the look-out for it ever since, and last week, when collecting at Tarawera, on the Taupo-Napier Road, I found it.
“I was searching under the trees at the top of the ranges for Cordyceps robertsii, and picked up a scaly bud like an immature cone. On looking about to see where it had come from I found a tuberous-looking mass, about 10in. by 6in., covered with the circular scars from which these small spike-buds had fallen. Disposed irregularly round the mass were two different kinds of brown scaly spikes, the male (?) being much longer than the female. Remembering that you asked me to examine the manner in which it was attached to the root of the tree, I removed as much as possible of the vegetable mould and decaying leaves which partially covered the plant, and, finding a small tuber, bearing two or three good spikes, apparently distinct from the main mass, I carefully cut away the root of the tree and placed it, with the plant and the surrounding soil, in a box, carefully packing it with moss so that it could not shift. I then cut two or three of the mature male and female spikes from the larger plant, which I left carefully covered with branches. I tried to trace the root on which it seemed to grow back to the trunk of the tree, and uncovered it all the way. Even then it was hard to say what tree it was, as three—a Fagus, a Pittosporum, and some other —had their roots closely intermixed. Some little distance away I found the remains of another small mass, which had been broken up by a falling tree…. I carefully examined the tuberous portion, and found that, although it rested on the root of the tree, there was no attachment of any kind, but a woody root passed down the lower part of the tuber into the ground : this, unfortunately, I had cut through. The representation given by Taylor is fairly good, but the tuber seems to be growing from the root of the tree instead of on its own, and must have been from a larger specimen than mine.”
Mr. Hamilton has suggested a question of considerable importance, one perhaps that can only be determined by watching the development of the plant from the embryo. In the large specimen presented to the Colonial Museum by Mr. Hill the woody rhizome viewed from below presents every
appearance of true root-parasitism, so far as can be determined without the destruction of the specimen; the same is to be seen in a specimen from Nuhaka which I exhibit to-night. At the same time, there can be no question that, as the woody rhizome extends over the surface of a large root, it adapts itself to the contour of the root without developing new organs of attachment—at least, in certain instances, probably in all.
On the other hand, I exhibit a young specimen the rhizome of which forms a small disc, scarcely exceeding lin. in diameter and ⅜in. in thickness; a tortuous woody root appears to have developed directly from the centre of the lower surface of the disc, and has attained a total length of 6in. or 7in. There is a very regular expansion of the supposed root upwards at the junction with the rhizome, and with our present knowledge it does not seem possible that this can have been produced by parasitism. For the present I hesitate to interfere with this root in any way until further specimens of a similar character can be obtained, when careful dissection of the point from which it is given off, and a microscopical examination of its structure, will doubtless throw light upon the subject. I have little doubt that specimens of this kind are more frequent than might be expected.
Mr. Hill assures me of his conviction that the plant is truly parasitic for the whole term of its existence, and that it never developes true roots. If we may suppose that it is at first parasitic and only produces true roots after attaining a certain stage of development, we have exactly the reverse of what takes place in such plants as Cuscuta, the radicle of which forms a true earth-root immediately after germination; but as soon as the stem produces haustella, which enable it to absorb the assimilated juice of some other plant, the root perishes. The process would be closely analogous to that exhibited by the native sandalwood (Fusanus cunninghamii), and the “eye-bright” (Euphrasia cuneata), &c., the roots of which become attached to those of other plants, and for a time at least absorb the chief portion of their nourishment in an elaborated condition. The facts, however, are still obscure, and much has to be done before the difficulties surrounding the subject can be properly cleared up. My only excuse for again drawing attention to Dactylanthus, while still unable to make any material addition to our knowledge of such an interesting organism, must be the hope I entertain that by this means the assistance of observers favourably situated for examining the plant in the living state may be more readily obtained.