Habit and External Form of Plant, and Nature of Strobilus.
It has long been recognized that as regards habit and external form these two sections are closely connected. The type species L. Selago and L. Phlegmaria are, of course, very distinct, the former being a short, upright, little-branched terrestrial form in which there is no differentiation between fertile and sterile leaves, the fertile zones alternating up and down the stems with sterile zones, and the latter being a much-elongated, pendulous, much-branched epiphyte in which there is a special sporophyll formation, the sporophylls being characteristically confined to the ends of the branches and the latter appearing as narrow whipcord-shaped strobili. But between these two extreme forms there are numerous species illustrating every grade of transition. The species which are grouped by both Baker and Pritzel under the heading Subselago possess the sporangia aggregated into quite easily recognizable terminal spikes which approach the Phlegmaria condition, although the transition from sterile to fertile leaves and from sterile to fertile regions of the stem in these species is very gradual. Also, included in both subsections Euselago and Subselago of Pritzel's Selago section are pendulous epiphytes and upright terrestrial forms, although on the whole there is seen to be a gradual transition in the section from the erect terrestrial form to the hanging epiphyte, this transition keeping pace with the transition in the fertile region from the Selago condition to the Phlegmaria condition. Again, in the Phlegmaria section are grouped forms some of which are robust and upright in growth, and others tender and pendulous; and of these the former possess short thick strobili in which the sporophylls show a more or less gradual transition from the sterile leaves, and the latter possess in some cases very distinct long whipcord-like strobili, while in others the fertile leaves may be not different from the sterile leaves. The New Zealand species which belong to these two sections present some very interesting transitions of this nature, which will be instanced.
It will be at once apparent that a classification which is based upon one character alone—as, e.g., the nature of the fertile region—is bound to be unsatisfactory. The general habit of the Lycopodium plant and its external form must be considered along with the nature of the fertile region, for these three characters are closely interdependent. That these two sections together constitute a natural division of the genus seems to be suggested by the fact that they show certain common growth-features which are markedly absent from the remaining sections. In habit they are consistently orthotropic, so that their extent of growth is strictly limited. As a result of this orthotropic manner of growth it is found that throughout the two sections the roots are confined to the basal region of the plant, as many as six or seven roots appearing in the cortex of the stem in a transverse section
taken at its base. Again, branching of the stem is dichotomous and in no case monopodial. Now, the study of the distribution of the species of these two sections as given by Baker or by Pritzel shows clearly that the terrestrial forms occur, on the whole, in colder regions and the epiphytic forms in warmer regions. It would seem, then, that the evolution of the subgenus Urostachya has been determined largely by climatic conditions. That this is so is seen to be more probable still from the fact that the external form of individual species is in a highly plastic condition, varying greatly according to the habitat. Whether we are to regard the Selago form as having been derived from the Phlegmaria form, or vice versa, must at present remain an open question. It will be decided only by a comparative examination of all the other Lycopodium plant structures, for it involves the question whether the genus as a whole is to be read as a reduction or as a progression series. Especially must it be considered in the light of fossil evidence derived from later geological ages than the Carboniferous. In the meantime, considering that the more complex members of the genus are those which show the greatest adaptation to the environment, the onus of proof must lie upon those who would trace in the genus a general reduction in form rather than a progression.
In the New Zealand biological region L. varium shows a remarkable variation in form according to locality.* In Plate IX, fig. 1, are illustrated three varieties. That named A is a plant which I have collected from the lower end of the Otira Gorge, where it grows abundantly in clumps on rocks and other exposed terrestrial positions. The Otira Gorge is situated on the western side of the Southern Alps, where the climate is exceedingly moist, at a height of about 1,500 ft. In Part I of these studies (16, pp. 254, 290) I have described the same form of this species as it occurs in enormous clumps on the floor of the excessively wet forest of Stewart Island. The plants are upright in habit, and the strobili characteristically curved. This habit is very similar to that of L. strictum Baker of the mountains of Madagascar, which is figured in Engler and Prantl (13, fig. 375). The plant of this particular form A is obviously akin to the typical form of L. Billardieri, differing from it in the rigid upright habit, the smaller size, and the short curved strobili, which are not quite so distinct as and are stouter than those of L. Billardieri. C on the same plate illustrates the same species as it occurs on the Dun Mountain, Nelson, in a drier, more exposed situation, and at a height of 4,000 ft. In this case the strobili in their tetragonous region are only from ½ in. to 1 in. in length, but the sporangia are continued still farther down the branches in the axils of gradually lengthening leaves. B shows two plants of this species as it occurs on the meadows of the Antipodes Islands.† In this particular variety the plants which occur in clumps stand only about 5 in. or 6 in. in height. They are very sparingly branched, and the fertile tips of the branches are very short and grade into the vegetative regions, as in the case of the form from the Dun Mountain. As well as these three forms of L. varium I have before me material of the same species as it occurs on Campbell Island, which was gathered by the Subantarctic Scientific Expedition of November, 1907. These plants are
[Footnote] * See Postonpt, p. 215.
[Footnote] † I am indebted to Dr. L. Cockayne for specimens of this form. Spirit specimens of L. varium from Campbell Island were kindly supplied me by Dr. Charles Chilton from material in the Canterbury College Laboratory. For the herbarium material of the Macquarie Island species, and also for that of most of the species in my collection from localities outside the New Zealand biological region, I am greatly indebted to Mr. T. F. Cheeseman.
only about 6 in. in height, and are very robust in form, with large leaves. None of the Campbell Island plants which I have seen show fertile regions, so that I suspect that they are not full-grown plants. They will, however, undoubtedly be identical with the plant from Campbell and Auckland Islands described by J. D. Hooker (18). He speaks of it as follows: “L. varium, in Lord Auckland's Group and Campbell's Island, is one of the finest of the genus; it grows nearly erect on the bare ground to a height of 1 ft. to 2 ft., branching upwards, copiously leafy, with large spreading leaves, bearing at the apices of the branches numerous pendulous or drooping tetragonous spikes 2 in. to 4 in. long. The stems of this species are often nearly the thickness of a swan's quill, with spreading leaves as broad as the middle finger. I have nowhere seen handsomer specimens of it than this island presents, and more constant ones, for it is confined to the woods, and does not ascend the hills, neither varying in the narrow belt it inhabits nor seeking other localities where it would be exposed to the influence of exciting causes.”
There is also an interesting form from the hilltops of Macquarie Island gathered by Mr. H. Hamilton, and identified by Mr. T. F. Cheeseman as L. varium. This is shown in the present paper in Plate IX, fig. 2, B. In a letter to the writer with regard to this plant Mr. Cheeseman says, “I have for the present referred the Macquarie Island plants to L. varium because a few of the specimens have the branches narrowed towards their apices, with smaller leaves, thus approaching the spicate character of a true varium. It also differs from typical Selago in the larger, broader, and more coriaceous leaves. Still there can be no doubt that it comes very close indeed to Selago.” This plant stands from 4 in. to 6 in. in height, and is copiously supplied with bulbils, the latter developing in profusion while still attached to the stem. The presence of bulbils would seem to be an argument in favour of relating this plant to L. Selago.
From these varieties it will be seen that L. varium stands midway between L. Selago and L. Billardieri, as Hooker pointed out. The external form of the plant approaches that of L. Selago in those localities in which the plant is exposed to a more rigorous climate, and on the other hand approximates to L. Billardieri in those varieties which occur in less exposed and shady situations. The character of the fertile region also varies along with the same change in the environment, the strobilus being less differentiated from the lower sterile portion of the stem in those varieties which are found in exposed positions.
It will be convenient next to consider the forms of L. Selago as they occur in New Zealand. In Plate IX, fig. 2, A, are shown two plants of L. Selago which were collected by me in damp beech forest at Lake Rotoiti, Nelson. This is a drawn-out, largely unbranched, rather straggling form, green in colour, with comparatively large spreading leaves, and is very similar in appearance to that which is figured in the frontispiece of Professor F. O. Bower's The Origin of a Land Flora. The sporangia are very apparent in numerous fertile zones over almost the entire length of the stems, but the number of bulbils borne on the stems is quite small. C (Plate IX, fig. 2) is this species as it occurs in open tussock country on the hills around Cass, in western Canterbury, at an altitude of 1,500 ft. and over. This is a very common form in all such situations. It is much shorter and more rigid than the shade form described above, and is more profusely forked. The leaves are short, ascending, and densely crowded, giving a cylindric appearance to the whole stem. In the lower parts of the stem, however, they are larger
and spreading, and in those regions the appearance of the stem corresponds more with the form A. In form C, however, the leaves are generally more or less reddish in colour, the particular plant figured being a bright golden red. The number of bulbils present is much greater than in the case of the forest form, but is not nearly so great as in the case of the Macquarie Island plant (Plate IX, fig. 2, B). There is a tendency for the sporangia to be confined to fertile zones in the upper half only of the stems where the leaves are of the short form. The tips of the branches where the sporangia are full assume quite markedly a special strobilar appearance, as will be seen by an examination of C, but this is only a pseudo-strobilar formation. However, it is instructive to compare the tendency, as seen in this form of the species, for the sporangia to be confined to the upper half of the stem with what Cheeseman says (as quoted above) with regard to the Macquarie Island plant. On the summit of Browning Pass, on the Southern Alps, at an altitude of 5,000 ft., I collected specimens of L. Selago which showed two very distinct forms. These are figured in Plate X, fig. 1, A, B. B corresponds very closely with the tussock-country form just described; but A, while it is similar to the former in its much-branched nature and short form, is yet very distinct. It is more flaccid in growth, and the leaves are large, green, and spreading, as in the forest form of the species. The upper parts only of the stem are fertile, and there is a very scanty development of bulbils. Now, the form figured A grew among grass in a small cavity in the ground partly sheltered by rocks, whereas that marked B grew in a more exposed position on the surface of the ground, but only a couple of feet distant from the other. This species must be in a very plastic state to be sensitive to such a small change in the environment.
To pass now to L. Billardieri. When growing as an epiphyte it presents a very constant form. The plants occur in clumps and are pendulous, being in extreme cases as much as 4 ft. or 5 ft. in length. They are abundantly branched in all regions of the stems, so that the whole clump is quite bulky in appearance. In the lower parts of the stem the leaves are large and spreading, but there is a progressive diminution in their size in the ultimate branches until the strobih are reached. The latter, however, are quite distinct from the adjacent sterile regions of the branches, by reason of the fact that the sporophylls are at once broadly ovate in shape, with a well-marked keel, and are closely imbricating, and are also consistently arranged in four orthostichies. The phyllotaxy of the strobili, joined with the presence of the keel on the sporophylls, gives the strobilus a very distinct tetragonous form. In Plate X, fig. 2, A, is shown a much-forked fertile branch, alongside of which is the upper sterile part of the stem to which it was immediately attached. C in the same figure is the fertile portion of a branch of L. Phlegmaria Linn. from Fiji, from which it can be seen that the differentiation between fertile and sterile regions is more distinct than in the case of L. Billardieri. A specimen of L. Phlegmaria from the New Hebrides Islands which I have also in my collection shows the same very sharp distinction between sterile and fertile regions, although in this case the sterile leaves are tenderer and the strobili are markedly finer and more thread-like than in the Fiji form. Also in both these tropical forms of L. Phlegmaria the sporophyll keel is much less developed than in L. Billiardieri, so that the strobilus is cylindric rather than tetragonous in form. In the extreme north of New Zealand I have frequently found L. Billardieri growing terrestrially amongst Leptospermum scrub on the kauri-gum lands. These plants are from 2 ft. to 3 ft. in height, and the
Fig. 1.—A, L. varium Complete fertile plant from Otire Gorge, Westland. B, L. varium var. polaris Two fertile plants from Antipodes Island. C, L. varium: Uppei portion of fertile plant from Dun Mountain, Nelson.
strobili are shorter than in the epiphytic form and are curved over. On the whole, I should judge that in form they come nearer to the typical L. Billardieri than to L. varium—even to that form of the latter which I have above described from Otira Gorge and from Stewart Island. Possibly we are to explain the existence of this terrestrial variety of L. Billardieri by the fact that the original epiphytic plants were forced to accommodate themselves to a terrestrial habit through the destruction of the old kauri forest which took place probably a century or so ago. At any rate, they represent a variety not far removed from L. Billardieri, and thus make almost perfect the chain of forms which can be traced from L. Billardieri, and, indeed, from the type species L. Phlegmaria, through L. varium to L. Selago.
Perhaps the most interesting variety of L. Billardieri is the form which is known as L. Billardieri var.gracile. This I have found growing very commonly on the trunks of the tree-fern Dicksonia squarrosa in the coastal bush in the Western Botanical District of the South Island. This was first described by T. Kirk (23, pp. 376–77), and is there illustrated. In the present paper two plants are shown in Plate X, fig. 2, B. This variety is a very graceful, slender, flaccid plant, and always quite distinct from L. Billardieri. It is seldom more than one foot in length, and is sparingly branched. The fertile leaves show a wide range of variability in form. In some specimens they are in no wise different from the sterile leaves, although it must be noticed, as we saw in L. Selago, that the leaves are always largest towards the base of the stem. In others the fertile leaves are more bract-like, and the fertile regions then approach somewhat nearer to the typical L. Billardieri form. The two plants figured show well this varying character of the fertile regions, in the case of the plant on the right the various forms of the sporophylls occurring in intermixed zones on the same branch. The whole of the upper region of the stem is fertile, there being no intermixture of fertile and sterile zones as in typical L. Selago, but the fertile region generally extends to half-way or more down the plant. In the figure the limit of the fertile region on the two plants is indicated by crosses.
Sir Joseph Hooker states both in his Flora Tasmaniae (20, pp. 155–56) and in his Flora Novae-Zelandiae (19, pp. 52–53) that L. varium, which in its ordinary state is very distinct, passes into L. Selago on the one hand, and, on the other, when it inhabits warmer latitudes, grows dependent from trees, is much branched, more slender and flaccid, and becomes L. Billardieri. In his Flora Antarctica (18) he expands more fully this view of a chain of forms uniting L. Selago through L. varium with L. Billardieri, drawing his illustrations largely from the varieties of L. varium as they occur in Tasmania. In the same place he also says that “the variations from it [i.e., L. varium] to Phlegmaria are not obscure, the variations of that plant being excessive.” In his paper cited above T. Kirk discusses the relation of the New Zealand forms L. varium, L. Billardieri, and L. Billardieri var. gracile to one another, and concludes, “I am compelled to consider L. Billardieri as merely one of the varieties of L. varium.” He proposes the following arrangement of the principal forms: L. varium Br.— (a) varium (the ordinary New Zealand form), (b) polaris (Campbell and Auckland Island form), (c) Billardieri, and (d) gracile. This arrangement certainly has the advantage of emphasizing the natural steps in the evolution of the forms concerned, although such a form as L. Billardieri deserves specific rank. It places the form gracile also in the right position
as a variation from varium rather than from Billardieri. The variety gracile is always quite distinct from L. Billardieri, and it would be a more startling reversion from that species, with its very distinct strobili, than it would be from L. varium, which, as has been emphasized above, is not so far removed from the Selago condition, unless, indeed, we are to take the view that the whole genus is to be read as a reduction series. It may be mentioned here that W. Colenso described the form now known as L. Billardieri var: gracile under the name L. novae-zealandicum (11, p. 275), noting that it grows as an epiphyte on fern-trees. He describes it as “a small species of the Selago section, apparently pretty closely allied to L. taxifolium Sw.,” and he speaks of L. varium as being its nearest New Zealand congener.