Art. XL.—On a Remarkable Instance of Double Parasitism in Loranthaceæ.
[Read before the Wellington Philosophical Society, 12th February, 1876.]
One of the most striking points of contrast between the Floras of New Zealand and the British Islands is afforded by the large proportion of shrubby parasites to be found in the former compared with the latter. New Zealand possess three genera of Loranthaceœ, comprising nine or possibly ten species, half of which have showy flowers. The British Islands, with a large Flora, exhibit only a single species, the well-known Mistletoe (Viscum album, L.) with unattractive flowers. Central Europe possesses only three or four species. Five genera, comprising about 28 species, are found in Australia, but even in this case, the proportion of Loranths to other flowering plants does not exceed that which is found in this Colony.
Instances of double parasitism in this order have been recorded, but they are of very rare occurrence. Viscum album has been found growing on Loranthus europœus, and one of the Australian species of Viscum exhibits a similar preference for various forms of Loranthus. In the “Hand-book of the New Zealand Flora,” Tupeia antarctica is said to be parasitic on Loranthus micranthus, but I believe that only a single instance has been observed.
When recently botanizing with my friend, Mr. J. D. Enys, on the mountain above the Broken River, at an altitude of 3000 feet, we had the pleasure of discovering a noble specimen of Fagus solandri whose wide spreading arms supported a most abundant and luxuriant growth of Loranthus decussatus, some of the branches being from eight to nine feet in length, in many cases bearing specimens of Tupeia antarctica, several feet in circumference.
In some cases two or more specimens were growing on the same branch, but these were invariably small, and, in the larger specimens, the portion of the supporting branch beyond the point of attachment of the Tupeia was usually dead or dying, showing that the Tupeia had absorbed a large portion of the nutritive juices necessary for the full supply of the foster parasite. From 20 to 30 plants of Tupeia were parasitic on the Loranthus on this single Fagus, but although L. decussatus and L. flavidus were plentiful in the vicinity, no other specimens of Tupeia were observed and no other instance of double parasitism during explorations extending over many miles.
The remarkable mode of attachment (see “Trans. N. Z. Inst.,” Vol. III., p. 161) of Loranthus decussatus was strikingly shown, numerous stems being given off at the point of attachment, and adhering to the foster plant for several feet, often inosculating.
Tupeia antarctica, on the other hand, gives off no stems, and is simply attached at its base.
It is worthy of remark that Tupeia antarctica is found parasitic on a greater variety of trees and shrubs than any other New Zealand Loranth. Loranthus flavidus, on the other hand, appears to be restricted to Fagus solandri.