Pterostylis Banksii, R. Br. ex A. Cunn. in Bot. Mag. t. 3172; Hook. f. Fl. Nov. Zel. i, 248 ; Cheesem. Man. N.Z. Fl. 679.
Pterostylis Banksii, which is by far the finest species of the genus found n New Zealand was first discovered by Banks and Solander at Mercury Bay in November 1769, during Cook's first voyage. Solander, in his manuscript Flora of Zealand, referred it to the genus Arethusa, but gave no detailed account of it, for he supposed that it was identical with an Australian plant described in another part of his manuscripts. It was not again seen unti 1826 when the talented and enthusiastic Allan Cunningham gahered it on the banks of the Kawakawa River, Bay of Islands. Since then it has been found to range through almost the whole length of the Dominion, from the North Cape to Stewart Island, and from sea-level to nearly 4,000 ft
P. Banksii is usually found along the sides of lightly wooded gullies or on the margin of forest lands, and sometimes occurs in considerable quantities. It is variable in size, sometimes attaining a height of quite 18 in. or even more, at other times barely reaching 6 in. Specimens of the sizes quoted above have been collected by myself in a single locality growing under uniform conditions; but, speaking generally, the taller specimens are found in sheltered places along the sides of ravines, and the smaller in more open situations. The large green flowers, often streaked with red or reddish-brown, and with the three sepals all furnished with long filiform tails, have a most curious and bizarre appearance, and always attract the notice of strangers when seen for the first time.
The most widely spread of the New Zealand species. It varies much in size and degree of robustness, the size of the flower, and in the length of the filiform tails to the sepals and petals, &c. Mr. Colenso has made no less than 5 species based upon what appear to me to be exceedingly slight and inconstant differences. After a careful study of his descriptions and specimens I must confess my inability to distinguish any of them, even as varieties.
North and South Islands, Stewart Island, Chatham Islands: Abundant in shaded places from the North Cape southwards. Sea-level to 3500 ft. October-November.
1. P. Banksii, R. Br. ex A. Cunn. in Bot. Mag. t. 3172.––Tall, slender, leafy, grassy, 6-18 in. high. Lower leaves reduced to scarious sheathing scales ; cauline numerous, sheathing the whole stem, usually overtopping the flower but often shorter than it, 3-14 in. long, ; 1/4-1/2 in. broad, narrow linear-lanceolate, acuminate, pale-green. Flower solitary, large, 2-3 in. long including the tails to the lateral sepals, green, often streaked with red or reddish-brown. Galea erect at the base and then curved forwards ; upper sepal produced into a long caudate often filiform point ; petals also caudate-acuminate or shortly filiform, but always much shorter than the upper sepal. Lower lip with the entire part broadly cuneate, the free lobes gradually narrowed into long filiform erect tails 1-2 in. long. Lip narrow linear-oblong, obtuse, its tip slightly exserted ; basal appendage curved, repeatedly divided and penicillate at the tip. Column slender, more than half the length of the galea, upper lobe of wings with an erect subulate tooth at the outer angle; lower lobe narrow-oblong, obtuse.––A. Cunn,. Precur. n. 313; Raoul, Choix, 41 ; Hook. f. Fl. Nov. Zel. i. 248 ; Handb. N.Z. Fl. 268. P. emarginata. Col. in Trans. N.Z. Inst. xv. (1883) 328. P. patens. Col. l.c. xviii. (1886) 270. P. speciosa. Col. l.c. xxii. (1890) 488. P. auriculata. Col. l.e. 489. P. subsimilis, Col. l.c. xxviii. (1896) 611.
Life History and Behavior
Evolution and Systematics
The remarkable fertilization of Pterostylis was first described by myself in the "Transactions of the New Zealand Institute" (vol v, p. 352 et seq.). The upper sepal and petals are connate into a hood, at the back of which the column is placed. The tip of the lip, which is extremely sensitive, hangs out of the entrance of the flower, thus forming a convenient landing-place for insects. When touched by an insect it springs up, carrving the insect with it, and thus enclosing it within the flower. The position then occupied by the lip is that shown in fig. 2 of the accompanying plate, and the insect is enclosed in the space between the lip and the column. The hood-like flower prevents any escape to the right or left of the lip, and as the lip remains closely appressed to the projecting wings of the upper part of the column as long as the insect is present, the only mode of escape is by crawling up the front of the column and passing between the wings (see fig. 4). In doing this, it is first smeared with viscid matter from the rostellum, which proiects at the back of the passage between the wings, and then drags away the pollinia, which can hardly fail to adhere to its sticky body. When visiting another flower it must pass over the stigma before escaping, and can hardly fail to leave some of the pollinia on its viscid surface. From the above it is clear that the fertilization of the flower depends entirely on the irritability of the lip. With the view of proving this, on one occasion I removed the lip from twelve flowers while young, so that insect visitors would not be compelled to crawl out of the flower by the passage between the wings of the column. When these flowers commenced to wither thev were examined, when it was found that they were not fertilized, and that not a single pollen-mass had been removed from the anther. I have also repeatedly placed minute insects on the lip, thus causing them to become entrapped, and in several instances I have seen these escape from the flower in the manner described above, bearing pollinia on their backs. The whole of the New Zealand species of Pterostylis are fertilized in the manner described above; and, according to the researches of the late Mr. Fitzgerald, it is also the manner employed in the Australian species.
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