Art. XVI.—Helichrysum dimorphum Cockayne—a Hybrid?
[Read before the Canterbury Philosophical Institute, 1st October, 1919; received by Editor, 3rd October, 1919; issued separately, 10th June, 1920.]
Helichrysum dimorphum was discovered by Cockayne near the confluence of the Poulter and Waimakariri Rivers and described by him in 1915. Another plant was found by the same authority at Puffer's Creek, which runs into the Broken River not far from its junction with the Waimakariri. The two localities are about ten miles apart. The species has not been found again.
I visited the Puffer's Creek locality in February, 1919, and took specimens. The object of this paper is to suggest that Helichrysum dimorphum is a hybrid between H. filicaule and H. depressum, just as H. Purdiei seems to be certainly a cross between H. glomeratum and H. bellidioides.
Helichrysum dimorphum is a strong climber. The plant has a lusty, thriving appearance, and the branches grow in very great profusion and are most thickly massed together. Climbing upon a plant of Coprosma propinqua it shows leafless branches in the open, and leafy branches wherever it is at all shaded. The flowers, which are not fully open in my specimens, are borne upon the leafless branches. H. depressum occurs close to it in the bed of the creek, and H. filicaule is, as usual in such localities, abundant all round it. The plant grows about 8 ft. or 10 ft. above the bed of the creek.
Helichrysum filicaule shows a distinctly scandent or semi-scandent habit whenever it grows among tall plants, such as Discaria or Leptospermum. I have collected specimens over 2 ft. in length at Akaroa and elsewhere, one of these being found in the immediate neighbourhood of the Puffer's Creek plant when I was unsuccessfully searching for it in 1917. H. depressum, on the other hand, has been observed growing in actual contact with plants of Discaria without showing any tendency to climb.
My suggestion is that H. dimorphum is a cross between the two, deriving its scandent habit from H. filicaule, and its strength and solidity of form, which enable it to become a true climber, from H. depressum. As regards the inflorescence, H. dimorphum appears to be more closely related to H. depressum than to H. filicaule. The flowers in my specimens are just sufficiently advanced to make this quite clear. The resemblance to the flower and involucre of H. depressum is very close indeed. The flower is sessile at the tips of the branches, as in H. depressum, not terminal on a long filiform peduncle, as in H. filicaule; and the involucral bracts in their number and arrangement are exactly like those of H. depressum, the involucre being rather cylindrical than hemispherical.
In support of the theory I should adduce the following considerations:—
(1.) In both its localities both H. filicaule and H. depressum are present at no great distance. In the Poulter locality the plant grows on the top of a high terrace (perhaps 60 ft. to 80 ft.) above the river, in whose bed H. depressum is abundant, while H. filicaule is present everywhere about it.
(2.) The leafy parts strongly resemble H. filicaule, and the leafless parts H. depressum.
(3.) The plant is of extreme rarity, and this would be accounted for, in part, if H. dimorphum were a hybrid between the two plants named.
Since the above was written I have observed the plant in great quantities on the Lower Poulter, on the Esk River near its confluence with the Waimakariri, and along the Waimakariri itself between the confluence of the Poulter and that of the Esk with that river. The Esk mouth is not much more than five miles from the Puffer's Creek locality.