Art. XV.—Ranunculus paucifolius T. Kirk: its Distribution and Ecology, and the Bearing of these upon certain Geological and Phylogenetic Problems.
[Read before the New Zealand Institute, at Christchurch, 4th—8th February, 1919; received by Editor, 24th June, 1919; issued separately, 10th June, 1920.]
|Comparison of Ranunculus chordorhizos and R. paucifolius||90|
|Habitat and Distribution— General||92|
|Details of Distribution||93|
|Associations of the Area||94|
|Ecological: Main Problems involved— General||96|
|Relation to Geological Problems||97|
|Origin of the Group to which it belonged||99|
Ranunculus paucifolius was “raised to specific rank” by Kirk (1899, p. 11), who separated it from R. chordorhizos Hook. f.
The notable points in his description are: “Leaves 1 or 2”; “Scape equalling the petioles”; “Achenes few, turgid, with a straight subulate beak”; “flowering season, December.”
Under R. paucifolius, Cheeseman (1906, p. 16) says, “Much more complete material is required before a good description can be given of this curious little plant. It is very close to the preceding species, but seems sufficiently distinct in the less fleshy and more coriaceous habit; fewer leaves, which are broader, and much less divided; longer scape, and broader petals. Only one flowering specimen has been obtained.”
From Hooker's account of R. chordorhizos it is evident that Ranunculus paucifolius was first collected by Haast before the publication of the Handbook (1867), though its discovery is accredited by Cheeseman to Enys (1906, p. xxxiii), where it is stated that Enys's work in New Zealand began in 1874.
Comparison of Ranunculus chordorhizos and R. paucifolius.
In 1918 I obtained flowers of R. chordorhizos from two plants in my garden at Christchurch brought from Mount Hutt (at c. 4,000 ft.) in 1917. One of those also flowered in 1919. The flowering-date in Christchurch (sea-level) was September. The flower is from 1 in. to 1½ in. in diameter. The petals are from 5 to 8, and even more.
The most striking feature of the flower (hitherto undescribed) is the form of the sepals, which are lobed like the radical leaves, and one of them in each flower is much larger than the rest, lobed and appearing like the cauline leaves which form a sort of involucre in R. Haastii, but attached so much higher that it should rather be termed a bract. The edges of the petals are also lobed shallowly. The colour of the sepals is dark like the leaves. I obtained one head of ripe achenes from my plants. The description of the achene in Kirk and Cheeseman seems to be quite exact.
Specimens of the plants here used were sent to Kew for identification; there are no flowering specimens there, but my plants were identified as R. chordorhizos. The locality (Mount Hutt) is not far from Mount Somers (the original locality), and the plant has been collected by Laing at Mount Winterslow, between Mount Somers and Mount Hutt.
I visited Castle Hill on the 8th November, 1919, and obtained specimens. There had been a heavy fall of snow on the 1st and 2nd November, and most of the flowers were much damaged. Between twenty and thirty blooms were observed. The flowering-date is late October and November, not December (Kirk, Cheeseman). I was able to get about a dozen specimens which had flowered after the disappearance of the snow. No buds were coming on, and the season was rather backward than otherwise.
The flower is large and showy, averaging about 1½ in. in diameter when fully expanded. I measured one exactly 2 in. in diameter.
The number of petals is from 5 to 8 or even more; the most usual number seemed to be 6. The sepals are 5. Most of the plants bear one flower only, but several were observed with two. The scape is very short, not more than 1 in. in any of my specimens. There are no cauline leaves as in R. Haastii; the sepals are pale yellow and have nothing of the peculiar character of those of R. chordorhizos. The edges of the petals, unlike those of R. chordorhizos, are entire or very nearly so, the margin being very slightly wavy.
I obtained ripe achenes at Castle Hill in December, 1918. The description in Kirk is inexact, and the achene is not distinguishable from that of R. chordorhizos.
I may add that I have in cultivation seven plants brought from Castle Hill in 1918. All are thriving, but none flowered in 1919.
The two species having been grown close together, the following points of comparison may be noted. The general coloration of the two is very similar and very curious; R. chordorhizos is, however, a little darker than R. paucifolius. The leaf of R. chordorhizos has the segments distinctly recurved; those of R. paucifolius are nearly flat. R. paucifolius is a good deal the larger plant in every way. The leaf of R. paucifolius is pitted, but not so deeply as that of R. chordorhizos. The leaves of both species are pitted when fresh, not only “when dry” (Kirk, Cheeseman).
To summarize the new facts resulting from these observations:—
R. chordorhizos has recurved leaves, pitted while fresh.
R. chordorhizos has a flower about 1½ in. in diameter (not “1 in.”)
The sepals of R. chordorhizos are lobed, and have something of the character of a cauline leaf or bract.
The number of petals of R. chordorhizos is from 5 to 8 or more.
The edge of the petals of R. chordorhizos is lobed or crenate.
The leaves ofR. paucifolius, instead of being only 2–3 (Kirk), are as many as 8. One of my plants in cultivation has 9 now. Six is quite usual. The name paucifolius is a misnomer.
The scape of R. paucifolius is not always solitary.
The number of petals of R. paucifolius is 5–8.
The flower of R. paucifolius is larger than described hitherto, being from 1½ in. to 2 in.
The flowering-date of R. paucifolius is late October and November, not December.
The achene of R. paucifolius is exactly like that of R. chordorhizos; the style is curved, not straight.
Conclusion from these Facts.
I have been tempted to think that R. paucifolius hardly deserves specific status, and that it should be reduced to the rank of a variety of R. chordorhizos; but in the light of the above observations I am compelled to decide that it should be upheld as a distinct species. While the differences in the cutting and the colour of the leaf, the size of the plant and of the flower, the edging of the petals, the pitting of the leaf, might be considered trivial, yet the character of the sepals of R. chordorhizos, constituting a distinct link with R. Haastii, would seem to be important enough, taken in conjunction with the other differences, to warrant the retention of the species. Until flowering specimens of R. crithmifolius have been studied it is not possible to tell how the group may ultimately be treated.
Habitat and Distribution.
The only known locality for Ranunculus paucifolius is a rock-bound hollow behind the farm buildings at Castle Hill, in the Trelissick Basin, about a mile and a half from the homestead of the late J.D. Enys, upon whose property the farm was situated.
A full account of the general geological features of the district is given by Speight (1917), with a map showing the Castle Hill itself (p. 323), and plates, of which Plate xxi, fig. 1, gives a view of the small hollow from above.
The locality of the species is a small synclinal basin forming a kind of amphitheatre. Its main direction is north-east and south-west, the north-east end being the higher. It is bounded on the south and west by the steep grassy slopes of Castle Hill, with frequent outcrops of limestone (seen in Plate IV), and on the north and east by piles of limestone rocks from 80 ft. to 100 ft. high, which are weathered into the usual fantastic shapes. It is entered from the eastern side by a gap in the limestone barrier about 100 yards broad; a small but constant stream rises on the south-west side of the basin, and flows through this gap on to the flat cultivated plains of the Castle Hill farm, which are overlooked by the steep limestone rocks. Except at this point the basin is surrounded on all sides by limestone rocks or steep slopes of grass upon a limestone soil. The weathering of the rocks by frost and wind produces a great amount of debris, which is blown far and wide by the strong winds of the Southern Alps, and this debris collects in the basin owing to its enclosed character. Within the basin a small dune-system is produced by the action of the wind, so that its floor is diversified by small
ridges and shallow hollows of dune type. The south-west half of the basin is clothed with tussock grassland, and does not concern us. The north-east half, at the south-west end, shows first (moving from south-west to north-east) a small area, about 120 yards by 100 yards, of open debris formation which does not harbour this Ranunculus. The upper (or north-eastern) portion consists of a larger area of limestone debris, about 350 yards by 100 to 150 yards, of which some parts are clothed with a half-closed tussock formation, others with an open formation, including the Ranunculus paucifolius, while some considerable portions are entirely barren. The bottom of this part of the basin is occupied chiefly by a belt of half-closed tussock formation; the eastern side has rapid slopes of coarse debris below the limestone rocks; the western side (shown in Plate IV) has a gentler gradient, and the grass-covered slopes of Castle Hill here ease off gradually into the central basin. Tongues of half-closed tussock formation, on this side, occupying higher ground or ridges, separate roughly circular or semicircular areas of the open formation well seen in Plate V, within which most of the plants of Ranunculus paucifolius occur.
The debris itself is of a flaky character, but is reduced, over most of the area, to a fine uniform powder. The colour of the bare patches is thus a pale yellow, deepening to brown in certain places, owing apparently to the volcanic element present in the limestone itself in varying quantity. The debris on the steep eastern slopes is much of it very coarse and rough, and very large flakes of the stone lie thickly here.
At the extreme north-east corner a dune formation is being broken up. Here are semicircular breaches of the higher dune, whence masses of very loose debris come down. At the top the slope is steep and the material deep and soft; hardly and vegetation can grow, and the line separating the tussock grassland from the perfectly barren space is sharp and clear.
Possibly all parts of the basin have at one time or another been thus closely covered, the covering being subsequently stripped away or buried, while a certain area must always have remained sufficiently open somewhere in the area for the calciphile community to exist.
Digging at a spot where several plants of Ranunculus paucifolius grew close together showed that the limestone debris was here exactly 18 in. deep. At that depth a more consolidated subsoil was reached. Down to this depth the material was perfectly uniform, fine and incoherent, and the roots of the Ranunculus, about 10 in. or 12 in. long, do not reach beyond this layer, which seemed fairly damp throughout at the end of a period of about a fortnight's fine weather. In a really dry season this material must, of course, become extremely dry.
Details of Distribution.
The following are the main results of the careful search of the whole, or nearly the whole, of the area, in which I had the assistance of Messrs. R. Speight, A. E. Flower, and Dr. W. P. Evans.
(1.) Most of the plants grow on the more gently sloping north-west side of the basin, and are most thickly congregated on two areas, each about 60 yards by 40 yards. The whole area within which all the plants (except three or four) were found is about 300 yards by about 60 yards— roughly, between 3½ and 4 acres.
(2.) Nearly all the plants were found on ground sloping at an angle of from 6° to 8°. Few were found on quite level spots, and none at all on very steep places.
(3.) Where several plants occur in a line, from 2 ft. to 4 ft. apart, as sometimes happens, this line takes no constant direction.
(4.) The plants occur, roughly, in groups, but seldom close to one another and not often very near any other plants. Only in one small area were they found among tussocks (about a dozen altogether), and here the tussock formation is peculiarly scanty.
(5.) The whole number of plants I counted was seventy. Allowing for possible errors and oversights, and portions not quite so minutely examined, it is safe to say, I think, that the area does not contain more than from one hundred and fifty to two hundred individuals, and I should think it probable that there are not more than one hundred.
(6.) In one space which was most carefully examined, and in which the plants were as frequent as anywhere, the nearest neighbours of a particular plant of Ranunculus paucifolius were: Poa acicularifolia, Lepidium sisymbrioides, Wahlenbergia albomarginata, Myosotis decora, Carmichaelia Monroi var., and the introduced Arenaria serpyllifolia and Cerastium glomeratum. The plants in the vicinity were on an average about 6 in. from one another, and spaces about 12 in. square were frequently quite barren. This would be a typical “open formation.”
In another case, not at all exceptional, at the other end of the area examined, a plant of Ranunculus paucifolius was seen to have no other plant nearer to it than 3 ft.; at this distance was a small patch of Poa acicularifolia; a little farther away was one plant of Oreomyrrhis andicola var. rigida, and at about the same distance one of Lepidium sisymbrioides; and 10 ft. away was one plant of Notothlaspi rosulatum. The rest of the 10 ft. circle was perfectly bare.
To complete the account of the surface of the hollow it may be added that areas of 12 yards by 6 yards were measured which supported no living plant of any kind. These completely barren spots form a fairly large part of the small available space.
Associations of the Area.
The small basin here described supports a limited community of calciphile xerophytes, of which Ranunculus paucifolius is a typical member. It supports also a good number of mesophytes, representing the usual flora of the district, and a fairly large group of introduced plants.
(a.) On the barest portions of the area, where the debris is deepest, loosest, and, in dry seasons, presumably driest, the only plants are Lepidium sisymbrioides, Oreomyrrhis andicola var., Oremyrrhis andicola var. rigida, the introduced Arenaria serpyllifolia, and occasionally Myosotis decora.
(b.) The usual open formation of the gentler slopes includes, besides the plant under consideration, all the above-named, and in addition Pimelea prostrata var., Notothlaspi rosulatum, Poa acicularifolia, Anisotome Enysii, Cardamine heterophylla var., Carmichaelia Monroi or nana, Wahlenbergia albomarginata, Anisotome aromatica; and, more occasionally, Ranunculus Monroi var. dentatus, Senecio Haastii, Crepis novae-zelandiae, Raoulia australis, that variety of Epilobium novae-zelandiae which is distinguished by its generally reddish colouring and pink flower, and Myosotis cinerascens Petrie.
All these plants are perennial, and all are very low in stature.
These two—(a) and (b)—might be said to form a Lepidium sisymbrioides association. This association presents a most singular and characteristic facies. The general background is a glaring yellow, shading into pale brown in certain patohes. Upon this ground the scattered plants of
Lepidium sisymbrioides make spots of very dull chocolate, which are confused in the general scheme with the paler browns, dull greenish-yellows, and greys, of Oreomyrrhis andicola, Myosotis decora, Anisotome Enysii, &c. The sparsely scattered plants of Ranunculus paucifolius become almost invisible in this environment, and play no leading part in determining the appearance of the whole unit. The whole effect is most peculiar; the calciphile flora gives the impression that it belongs elsewhere—to another age, another climate and country. Much the same effect is produced, in my experience, by the isolated patches of ancient fen vegetation which survive at such spots as Wicken and Cottenham, set like savage aliens of some older and vanishing race in the midst of the green crops and pastures of modern Cambridgeshire.
(c.) As the formation becomes more nearly closed, on the borders of the grassy closed areas, Plantago spathulata appears in great quantities, and the closed formation of the immediate neighbourhood includes Festuca novae-zelandiae, two or three others of the usual grasses of the district, Raoulia subsericea, Hydrocotyle novae-zelandiae var. montana, Vittadinia australis, and a fair amount of moss. Here occasional plants of Lepidium sisymbrioides appear, but not far from the pure limestone patches.
(d.) The chief introduced plants which occur in the basin are Arenaria serpyllifolia (extremely abundant everywhere—more so than any native plant), Cerastium glomeratum, Hypochaeris radicata, the large ox-eye daisy (which completely covers the slopes on the eastern side of the rocks outside the basin), and Verbascum Thapsus. It is not without significance, as showing the very special and peculiar character of the locality, that Hypochaeris radicata, elsewhere so exceedingly abundant in New Zealand, is here comparatively rare.
It must be added that the rocks above the basin and the steepest slopes around them also harbour Epilobium gracilipes (which never occurs on the flat), Senecio Haastii (which is comparatively seldom seen below), Senecio lautus var. montanus, and a good number of such shrubs as Coprosma propinqua, Discaria toumatou, and Aristotelia fruticosa. Upon these shrubs the peculiar parasite Korthalsella clavata is found; this also grows upon shrubs in other limestone rocks (e.g., those at the junction of the Porter and Broken Rivers), but apparently is found only in the Castle Hill district.
A certain number of these plants are definitely calciphiles, and occur in no other situations; others seem to grow by preference on limestone, but are not confined strictly to it (in this district, at any rate); and the rest are of general distribution.
In the first class are Ranunculus paucifolius, Poa acicularifolia, Korthalsella clavata, Epilobium gracilipes, Myosotis decora, Anisotome Enysii. In the second are Oreomyrrhis andicola var. rigida and Crepis novae-zelandiae.
Several of them exhibit marked xerophytic characters, as described by Cockayne and Laing (Speight, Cockayne, and Laing, 1911, p. 358), and among these Ranunculus paucifolius is conspicuous. It has the pale ashenpurple colouring which distinguishes the shingle-slip plants generally, such as its relations Ranunculus chordorhizos, R. crithmifolius, and R. Haastii, Lepidium sisymbrioides has special adaptations, of which the disproportion ately long root is most remarkable (Cheeseman, p. 42). Anisotome Enysii shows a colouring very similar to that of Ranunculus paucifolius. There is here a marked degree of epharmonic convergence.
These plants make up a community of intense interest, and the problem of their existence is bound up with that of Ranunculus paucifolius, whose limited distribution and feeble powers of reproduction help to put that problem in a clearer and more striking light.
Ecological: Main Problems involved.
These problems may be thus stated: How are we to account for the survival, in an exceedingly limited area, of a very special and peculiar formation, and in very limited numbers, of a plant which is obviously adapted to a climate very different from that of the present time, which reproduces itself only by seed, not vegetatively, and that only in a very sparing manner, and which apparently can exist only upon a kind of soil occurring only in limited areas separated from one another by great distances?
Apart from geological history several considerations may here be given as bearing upon the main problems.
Reproduction and Distribution of Seed.—The achene, on dropping off, no doubt falls into the soil and is moved by the wind, as the surface of the debris is quite unstable, most of the plants being actually buried in it above the rootstock. It is remarkable that none of the plants of this association is a “traveller.” The seed of all is presumably distributed in the same way—by the action of the wind in shifting the soil; none of them is provided with a pappus or coma; no composite plant except Raoulia australis enters into the unit. Epilobium gracilipes and Senecio Monroi var. dentatus, which occur on the steep slopes and rocks above the basin and have seeds specially adapted for carriage to a distance by the wind, are absent altogether from the flatter portions of the area.
Instability of Soil.—The wind is always bringing fresh debris into the basin, and is always stirring and shifting all that part of the surface which is entirely or nearly bare. As the rocks are now always rapidly crumbling, and no doubt have been in the same state for a very long period of time, it follows that they must formerly have been much larger than they are now; therefore they must formerly have set free annually a much larger amount of material, and therefore the superficial area of unstable debris must formerly have been much greater. But in recent times the area of bare debris could never have been really extensive, as the accumulation of it would hardly be possible under present conditions except within the enclosed space of the basin. However, in some much older age it may be imagined that a much greater area lying eastward of the small basin might during a period of steppe climate or drought become a semi-desert, mainly of this debris, supporting a calciphile and xerophytic flora, in open formation, of such individuals and in such disposition as we now see within the enclosed and protected area only.
Struggle for Life.—As Warming (1909, p. 256) observes of fell-field in general, the typical xerophytic plants are so thinly distributed that they do not interfere with one another nor compete with one another. It is so here, and it is so upon the steep shingle-slopes of the dry eastern mountains of the neighbourhood. Ranunculus Haastii, for instance, is exactly like R. paucifolius in this respect. Only a certain small number of plants grow within a given space, when, so far as one can see, an infinitely greater number might grow there without in the least inconveniencing their neighbours.
Thus Ranunculus paucifolius has not been threatened with extinction in this manner. It seems, however, to have had to face two other dangers in recent times. On the one hand, if the surface upon which it grows were for any cause to become still more unstable, and the wind to act
more violently and continuously upon it, the plants might all be buried, as some of them no doubt have been. On the other hand, if the supply of material delivered into the basin should diminish and finally cease altogether, no doubt the closed tussock formation which now covers the south-west portion of it would gradually invade the whole, and Ranunculus paucifolius would die out. This, it would seem, must ultimately happen.
The area has for many years been open to stock and rabbits, but they evidently do not care for the plant, otherwise it would have perished long ago. There are plenty of rabbits now in and about the basin. The openness of the formation has no doubt protected the plant from destruction by fire, a great and very real danger in New Zealand.
Influence of Slopes.—The fact that it is confined to the easier slopes— almost to level ground—is also of very great significance. Among its associates, for instance, Lepidium sisymbrioides and Myosotis decora easily maintain themselves upon very steep slopes, and consequently these plants are quite widely distributed, occurring, in the immediate neighbourhood, upon the limestone slopes at and near the junction of the Porter and Broken Rivers, and upon those of the Whitewater River and of the Upper Porter or Coleridge Creek, whereas Ranunculus paucifolius, by reason of its apparent inability to grow except upon easy gradients, is debarred from these areas, where every condition which it requires is to be had except this one, and can maintain itself only within the very limited basin where it is presumably doomed ultimately to perish.
Limestone Soil.—When it is said that the plant can exist only in limestone soil, it is not denied that it might live, if transplanted or sown, in some other soil; but the assumption is that in any other soil, if it can live at all, it cannot compete with the ordinary vegetation of that soil: it could live, that is, only under artificial conditions and when protected.
Relation to Geological Problems.
We may now consider what conditions are indicated as most probable in the remote past of this community in general and of R. paucifolius in particular.
It seems inconceivable that the plant should have “originated,” established itself, and subsequently maintained itself for countless ages, all within the narrow limits of its present distribution, and the first condition requisite for its establishment would be the existence of a very much larger area of continuous Tertiary limestone strata than is now to be found anywhere in New Zealand.
This area need not have been—and, indeed, could not have been—one continuous sheet of limestone beds covering the whole of the district within which the isolated fragmentary remnants now exist. But the inference here drawn from the existence of this whole calciphile unit, and of Ranunculus paucifolius in particular, is that these beds must once have been more extensive and more nearly continuous than they are now. The ancestral Ranunculus may well have existed upon soils of pre-Tertiary origin and developed there its xerophytic characters, while one form of it established itself especially upon the limestone, developed characters accordingly, and ultimately become virtually incapable of maintaining itself elsewhere. This is, at any rate, one hypothesis which seems to fit the facts. But the exact sequence of events can here, in the nature of things, be only a matter of conjecture.
This comparatively wide area must have had, at some remote period, a steppe or semi-desert climate, under whose influences a xerophytic and partly calciphile flora developed and flourished, and it is likely that what we now have represents only a portion of this flora, many species having probably died out altogether.
This area must have been partly a peneplain (upon which alone R. paucifolius, it would seem, could “originate” and flourish), and would probably be conterminous with a range or ranges of hills with limestone rocks exposed and weathering into dust exactly as they now do on the small area here under observation. But such peneplain need not have consisted entirely of Tertiary limestone beds.
The area would be in the nature of a strip or belt, of no very great width and probably much interrupted, corresponding roughly to the shoreline or lines of the hypothetic Tertiary sea or seas. It would be conterminous with and more or less alternated with an area or areas of pre-Tertiary formation, probably lying to the north and east, as posited, e.g., by Cockayne (1911, pp. 343–44), by way of which probably the mesophytic flora would return when a more humid climate should prevail in this area. Upon this pre-Tertiary area the related species, R. chordorhizos, &c., would have originated and flourished, or that single species or form from which they and R. paucifolius trace their common descent.
The greater part of these limestone beds was destroyed by erosion of various kinds in subsequent ages, leaving only the present small isolated remnants, of which the Trelissick Basin is one of the largest.
It is impossible that by the elevation of the land 3,000 ft. or 4,000 ft. (Haast, Hutton, Park), and the consequent refrigeration and glaciation, the whole flora of the district (as has been thought) was driven to another tract, now non-existent, and returned with the subsidence of the land and consequent change of climate. “Return” of a calciphile flora over areas upon which the Tertiary beds had becn destroyed would be impossible, especially since, as we have seen, this flora as a unit is not a “traveller”; and we cannot escape the conclusion that this plant community has been represented within the area of the small basin, since it first established itself or “originated” in that neighbourhood.
Glaciation bears upon the question in two ways:—
(1.) Hutton (1900, p. 176), followed by Cockayne, correlated the supposed drought epoch, of which our flora shows signs, with the glacial epoch, which he placed in the older Pliocene period. This view was adopted by Cockayne (1901, pp. 280 et seq.); but that authority believed that at the height of the glaciation the eastern mountains (within which this area is included) might still support a xerophyte flora like that of the shingle-slips of the present day (Cockayne, 1911, pp. 348 et seq.).
The view of Speight (1911) and others is that the last glacial epoch is much more recent, that the drought period was correlated with it (Cockayne, 1911, p. 344), that the Tertiary deposits were continuous over a much larger area than is the case now (Speight, 1915, p. 54), that the Castle Hill area probably escaped glaciation altogether (Speight, 1917, pp. 323 et seq.), and that the Trelissick Basin at the height of glaciation was “probably a snowfield” (Speight, 1917, p. 323).
It would seem certain that a steppe climate or period of drought must have obtained here over a large area at least once (probably more than once) since Tertiary times, but to the present writer it seems quite uncertain whether this was coeval with and resultant from the glacial epoch or not
and the analogy of other lands would seem to show that such a climate may have existed in New Zealand independently of any glacial epoch, whether that epoch be (with Hutton) older Pliocene or (with Speight and others) Pleistocene. The question whether the “drought” be Pliocene or Pleistocene is here dwelt upon because, whatever conditions obtained and whatever balance was established at the end of the “drought,” if that “drought” were Pliocene that balance must in all probability have been disturbed and a new set of condition reached when the later Pleistocene glacial period came. The problem is then, to discover what were the conditions during and after some more recent period, rather than during and after the exceedingly remote period of any possible Pliocene glaciation and concomitant steppe climate.
(2.) Glaciation also has been supposed to have been the chief, though not the sole, eroding agency by which the great area of Tertiary beds was destroyed (Hutton, 1885, p. 92; Speight, 1915, p. 337). The question of the agency by which, and the probable period during which, these beds have been destroyed is, however, one of secondary import in this connection. It is enough, for the botanical problem, if it is decided that they once existed, have been in one way or another largely destroyed (being now represented by the small isolated fragmentary areas which remain to us), and that the Trelissick Basin (including the small area here studied) escaped glaciation and any great degree of refrigeration during any glacial epoch. We may then imagine the ancient birthplace and habitat of Ranunculus paucifolius and its associates to have been a semi-desert area of flat or flattish plains diversified with ridges and islets of higher ground, and neighboured closely by a range of limestone hills or even mountains. The whole landscape would have a yellow hue; upon the surface large areas of unstable shifting debris would possibly alternate with ridges of more grassy and closed formation. Strong winds would be frequent and dust-storms violent. The vegetation would be sparse and harsh, including the species here described, and no doubt many others which have perished; a pale-purple, greyish, and brown colour scheme would predominate. The land would be occupied by no animals save lizards and birds, its whole appearance being monotonous, parched, and glaring; while the dreariness of the scene would be enhanced by the setting of pallid limestone rocks of grotesque and fantastic form—chessmen, collar-studs, sea-lions, and gorilla torsos. The general appearance of the limestone desert might be much like parts of the Sahara—e.g., as figured in plate 345 of Schimper's Plant-geography, p. 614.
If Speight's (1911) hypothesis of a pluvial climate in post-glacial times be accepted—and certainly the-evidence collected by him seems to be conclusive—this community and others like it must have passed through and survived such a period, unless the districts in which they exist have been specially favoured. There is little or no reason to suppose that this was so, for, although Cockayne (1900) mentions that the Trelissick Basin is now very dry climatically, old residents do not support this view; and, in any case, the fact, if established, that it is now dry does not prove that it was always so in the remote past.
Origin of the Group to which it belonged.
With regard to the historical development of this group of Ranunculi, if the neo-Lamarckian view of the origin of species be adopted—the theory
of direct adaptation or self-adaptation, as understood by Warming (1909) —it would seem probable that a single ancestral form of Ranunculus developed under conditions of extreme drought into a typical xerophyte, and that, after the conditions to which it had adapted itself had been modified or completely changed, this plant maintained itself against the competition of a mesophyte flora in certain localities—i.e., shingle-slips—in which it had an advantage, and in course of a long period of time, existing only in isolated areas completely separated from one another (one of which is the limestone area here described), it developed those comparatively trivial distinctive characters (especially in the cutting of the leaf) which now distinguish the “species” from one another.
According to De Vries (1912), however, such speculations and conjectures as to the conditions under which a species originated are idle, and can achieve no result. Speaking of “beautiful adaptations” to local conditions, he says: “In no case is it possible to tell whether the species have acquired these during their migration or during their stay in the new environment, or perhaps previous to their being subjected to the influence in question” (p. 592). Again: “Adaptations to new conditions [which are conceded] depend upon characters which were inherent in the species before it arrived in the new environment. The characters themselves are not the effect of the external influences considered” (p. 579). Such characters, it is contended, cannot be good specific marks; they fall within the range of “fluctuations” (as distinguished from mutations) and “cannot lead to constant races” (p. 540). The species thus modified or adapted remains essentially the same, and will, if replaced in the favourable conditions, resume its older form (as in the classic experiments of Cockayne upon seedling forms, and those of Bonnier upon alpine plants). The sole condition required in the plant is therefore “high plasticity.” We must not say that a species originated under the stimulus of its environment, or that it acquired new characters in response to changed conditions: that would be confusing cause and effect. “Fitness for present life-conditions… can hardly be considered as a result of adaptation, and we have to recur to previous hypothetical environments to explain the much-admired adjustments. All speculations of this kind are merely reduced to more or less plausible and more or less poetical* considerations” (p. 574). It is concluded that “geological changes of climate may have been accompanied by the production of new forms, but there is no evidence that this has occurred in such a way as to provoke directly useful changes”; that “the characters of local and endemic types do not betray any definite relation to their special environment”; and, finally, that “the facts which are at present available plead against the hypothesis of a direct adjusting influence of environment upon plants, and comply with the proposition of changes brought about by other causes and afterward subjected to natural selection” (p. 595). The author then restates his personal belief “that the species-making changes occur by leaps and bounds, however small.”
If these conclusions be accepted, the case of Ranunculus paucifolius and its associates may be thus considered in their light. It is generally accepted that a period of more or less severe drought or “steppe climate” has been passed through by a great part at least of the flora of New
[Footnote] * The writer explains in a footnote that this epithet is not intended to convey any reproach.
Zealand. The particular community here studied shows this with especial clearness, consisting as it does of a small association of plants all of which show very definite xerophytic adaptations, while some of them can exist only under certain very special and peculiar edaphic conditions such as may have obtained more widely in the past. The conditions governing plant-life before and during this period of drought may be supposed to have been much the same as those of the Sahara at the present time, thus described by De Vries (after Battandier): “Originally this region must have had an ordinary degree of rainfall and moisture…. Then… the rainfall must have slowly diminished, taking centuries… to reach the conditions which now prevail. The consequent changes in this flora must have been correspondingly slow, and must have consisted mainly in the disappearing of the larger part of the species; first of those which were dependent on the higher degree of moisture; then of others; until at the present time only the most drought-resisting forms are spared” (pp. 589–90). He proceeds to show that no specific changes, probably, were brought about by this process; that a large number of the species of this arid region are monotypic genera, each genus consisting of a single species; whereas, “if there had been any degree of adaptation during this whole period of increasing dryness, new species would have been produced —from those forms which by their own inherent capacities would be the very last to be threatened with extermination. These genera would therefore have produced quite a number of smaller or even of larger species, adapting themselves more and more to the changing conditions and stocking the desert, in the same way as other deserts have been stocked, from adjoining countries!” As this has not happened, it is concluded “that the single species… have not undergone any change in the direction of drought-resistance, but have simply been those which happened to be the best fitted for the life in the desert. A thick epidermis, a small display of leaves, long and deep roots, were the main qualifications for this choice” (p. 590).
Then, in our case, we assume that the moister climate re-established itself; the mesophyte flora which had been destroyed here, but had maintained itself in some adjoining land where the conditions remained favourable, returned and gradually repeopled the desert or semi-desert, while the xerophytes retreated before it to those places, such as shingle-slips and areas like the small hollow at Castle Hill, where they had an advantage and have subsequently maintained themselves. But, in contradistinction to what has been said above, we must accept the following propositions as to this community of plants:—
(1.) The species here studied—e.g., Ranunculus paucifolius, Lepidium sisymbrioides, Oreomyrrhis andicola var. rigida, and Poa acicularifolia— all existed and held their own among the pre-drought mesophyte flora, but not perhaps exactly in their present form, since “adaptations” are not denied except as differential marks of new species. The only alternative is that they have originated, some or all of them, since the period of “drought.”
(2.) All these species must have had a high degree of plasticity, and thus they are able gradually to accommodate themselves to the increasingly severe drought; but all must have had already, at the beginning of the period, a definitely drought-resisting structure, and this was not at any time acquired by any of them in response to any external stress, and it would be at first quite useless to them.
(3.) Each of these species originated by a mutation or sudden change involving the introduction of at least one quite new unit-character,* and this must have happened at some period anterior to that of the drought, not as a result of any such condition. Like other differential characters in general, those induced by this mutation would be at first perfectly useless (De Vries, 1912, p. 534), and the changed form would get its advantage only by the chance of the occurrence of the drought. The new character or characters then became useful; but we must resist the temptation to regard the useful character (e.g., the excessively thick and coriaceous leaf or long thick roots of the xerophytic Ranunculi) as an adaptation to the needs of the new external condition.
(4.) As “adaptations” can in this case not be denied, it follows that all the changes which are truly “adaptations” in these species are of the nature of “fluctuations,” and if any of them be cultivated under more favourable conditions the “adaptations” will disappear; the plant will then retain only so much of its xerophytic character as it had at the beginning of the drought, which gave it its initial advantage over others, and which was the result of some previous mutation. Until each plant of the community, therefore, has been so transplanted and tested it is impossible for us to tell which of its characters ought, and which ought not, to be regarded as differential specific characters; and it follows that the status of each is doubtful except where the plant has no near relatives at all among existing plants.
(5.) It is very improbable that the species of this community were all produced in the early stages of the drought by mutation. It is assumed “that the origin of new forms is not due to a hard struggle, but is promoted by a luxuriant environment and by easy conditions of development” (De Vries, 1912, p. 520). It is shown that a species (or genus) which is in a “state of mutability” may produce whole groups of new forms, even “swarms” (as in the case of Draba or Viola in Europe), though sometimes apparently such changes are only sporadic (p. 549). In this case it must be supposed that at some more or less remote period before the drought each of the genera Ranunculus, Lepidium, Oreomyrrhis, Myosotis, and Poa passed through a “mutation period” and threw off numbers of new species, some of which would immediately perish, while others would maintain themselves for shorter or longer periods under the stress of natural selection, and finally the species here perpetuated would alone survive under the fierce stress of the drought until rejoined by their relatives under the new climatic conditions.
(6.) Narrowing down the proposition to the particular genus and species here studied, we must believe that there existed at the beginning of the period of drought a species (or possibly more than one) of Ranunculus which had originated by mutation at some period (as to which it is useless to speculate) having peculiarly thick leaves, long roots, and other characters which gave it an advantage when the drought began to be severe. These characters, however, had been acquired by it owing to causes which are completely dark to us, not in response to any external stimulus or stress of environment. Fortunate in possessing these characters, it continued to live when other less-favoured Ranunculi perished, and it may or may not have changed under the new conditions, adapting itself thereto. But if it did so change it acquired no new unit-character; and all its modification remained mere “fluctuations,” and under more favourable conditions
[Footnote] * One is enough (De Vries, 1912, p. 562, in re Oenothera gigas).
would disappear and leave it as it had been when the drought began. The five species here treated as a collective group would represent varying degrees of “adaptation” of this kind, and none of them is a true species, or even a microspecies, unless it already possessed its distinguishing specific characters at the beginning of the period. In this respect Ranunculus paucifolius is like any of the others of the group, and it is impossible for us to tell whether it originated from the same ancestral form with them or was already a true species when the stress of drought came upon it. Its “adaptation” to a limestone soil is thus most probably not a specific character, but an adaptation of the unstable kind which may disappear as soon as the need for it is withdrawn. The test of cultivation can alone decide this point.
It would be beyond the scope of this paper to discuss all the difficulties which stand in the way of a full acceptance of these propositions. But it may be said that the words “however small” (“Species-making changes occur by leaps and bounds, however small”) seem to imply a very great concession. Changes of the nature of “adaptations” to new conditions are not denied (De Vries, 1912, p. 579). “It is clear that we may call all these changes adaptations to new conditions. But then we must concede that these adaptations depend upon characters which were inherent in the species before it arrived in the new environment.” And, as very small changes may be due to true mutations, there seems to be no very great difference between the opposing views. It is admitted that under new conditions a species may change very greatly and appear to become quite a different species, and it is admitted that under new (as under any other) conditions a species may acquire very small new characters by mutation and so become a new species. Is it not possible that the “state of mutability,” whose causes have hitherto remained obscure, may be induced by the impact of new conditions and the demands of a new stress? No very great adjustment seems necessary to reconcile this view with that of De Vries. He says that plants may change and adapt themselves gradually to new conditions, but no new species can originate in that way; changes so induced are not “mutations.” It may be suggested, on the other hand, that possibly new characters, due to “mutations,” may be acquired by the plant as a direct response to Nature's ultimatum, “Change or die!”
1. The original description of the species by Kirk is not quite accurate. The number of the leaves is not abnormally small, being frequently 5 and may be as many as 9. The style, when the achene is ripe, is curved, not straight. The flowering-period is late October and November, not December. The petals number 5 to 8.
2. It is one member of a xerophytic plant community, or association, of very ancient origin, and is specially adapted, like some others of that community, to live upon a limestone soil, or, rather, debris formation.
3. Though its habitat is now, so far as is known, extremely restricted, it must formerly, with its associates, have been distributed over a far more extensive area of Tertiary limestone beds. This conclusion supports that reached by Speight (1915, p. 345) upon quite different evidence.
4. It is the product of a period of drought or steppe climate, which directly caused the development of its xerophytic characters; and in this it resembles the other members of the community to which it belongs, one which was formerly, in all probability, far richer in species, and perhaps even in genera, than it is now.
5. It is adapted only for life under very special and peculiar conditions— e.g., its confinement to gentle gradients and to a limestone soil—which conditions have been provided and preserved for it, by a series of fortunate chances, in one small locality only (so far as is known at present).
6. Its life-history may be thus summed up conjecturally: Originating in the very remote past during a period of drought (which was probably very long) somewhere within or not far from an extensive area of Tertiary limestone, this plant acquired marked xerophytic characters and flourished, maintaining itself with ease, and as the area upon which it grew was slowly and gradually eroded (or perhaps, in parts, more rapidly by glaciation) it was restricted to areas continually diminishing in size and farther and farther separated from one another, until it remained in only one very limited area peculiarly situated and adapted to its needs. Here, as in its original state, it had little or no severe competition to meet and overcome, and for countless ages it has continued to exist there, surviving at least one great period of glaciation, which its habitat escaped; at least one pluvial epoch, which could not be favourable to it; and finally the various dangers resultant upon human occupation—depredations of stock and of hares and rabbits, pests and blights, and agricultural necessities and accidents, such as the plough and the wax match. Thus within its own narrow nook, secure from the competition of rivals, this strange plant, relic of an earlier day and clime, is passing slowly and, it may be permitted to fancy, unreluctantly away before our eyes in an age-long euthanasia.
I desire to express my great obligation of Mr. R. Speight, who with infinite trouble and pains took photographs of the plant in situ and of the locality; to Dr. W. P. Evans, who also photographed and sketched the locality and took the necessary observations of heights and levels and the measurements of the area; to Mr. A. E. Flower, who, with Dr. Evans, assisted me in the task of counting the plants; and to Dr. L. Cockayne, who has most kindly read over the whole of the paper and given me the benefit of his invaluable suggestions and criticisms.
Cheeseman, T. F., 1906. Manual of the New Zealand Flora.
Cockayne, L., 1900. A Sketch of the Plant Geography of the Waimakariri River Basin, considered chiefly from an Ecological Point of View, Trans. N.Z. Inst., vol. 32, pp. 95–136.
— 1901. An Inquiry into the Seedling Forms of New Zealand Phanerogams and their Development, Trans. N.Z. Inst., vol. 33, pp. 265–98.
De Vries, H., 1912. Rice Institute Book of the Opening Lectures on Mutations in Heredity and Geographical Botany.
Hooker, J. D., 1867. Handbook of the New Zealand Flora.
Hutton, F. W., 1885. Fauna and Flora of New Zealand, Ann. Nat. Hist., vol. 15, pp. 77–107.
— 1900. The Geological History of New Zealand, Trans. N.Z. Inst., vol. 32, pp. 159–83.
Kirk, T., 1899. Students' Flora of New Zealand and the Outlying Islands.
Speight, R., 1911. The Post-glacial Climate of Canterbury, Trans. N.Z. Inst., vol. 43, pp. 408–20.
— 1915. The Intermontane Basins of Canterbury, Trans. N.Z. Inst., vol. 47, pp. 336–53.
— 1917. The Stratigraphy of the Tertiary Beds of the Trelissick or Castle Hill Basin, Trans. N.Z. Inst., vol. 49, pp. 321–56.
Speight, R., Cockayne, L., and Laing, R. M., 1911. The Mount Arrowsmith District: a Study in Physiography and Plant Ecology. Trans. N.Z. Inst., vol. 43, pp. 315–78.
Warming E., 1909. Oecology of Plants.
This paper has been submitted to Professor Hugo de Vries, and he has sent me this comment:—
“It is, of course, interesting for me to read a statement of my views from a neo-Lamarckian standpoint, and the concession that the facts described by you do not contain any argument for a decision between the two contrasting theories.
“For me your article shows that R. paucifolius, R. chordorhizos, R. crithmifolius, and R. Haastii must have had a common ancestor, which was already a xerophyte, and that they must have inherited this character from it. This ancestor may have had the same geographical distribution which is now shown by the aggregate of its descendants. Perhaps one of them is identical with it; perhaps it has wholly disappeared. Under what conditions it lived we can, of course, not know, nor where and when it acquired its xerophytic properties. To conclude that it must have acquired them in a period of drought would be a circulus vitiosus, since it would simply be applying the theory to a special case and then considering the case as a proof of the theory.
“You say that possibly new characters may be acquired by a plant as a direct response to Nature's ultimatum, ‘Change or die.’ This is the old view, but not mine. The article you quote from was just intended to show that, as far as we know, the response has, as a matter of fact, always been, ‘I cannot change at your will and so I must die.’
“You assume that your plants have passed through periods of moisture, but have retained their xerophytic character nevertheless. It seems to me that this is conceding that external conditions do not, as a rule, provoke corresponding useful changes. They may do so, or seem to do so, or they may not. My view, that mutations, although, of course, caused by external conditions, are not necessarily responses to the ‘demands of a new stress,’ seems quite adequate to interpret your facts. I gladly concede that the causes of mutations are still dark to us, but then I say that responses such as Warming and other neo-Lamarckians suppose are far darker. Especially if you take into consideration what is now known concerning the structure of chromosomes and the distribution of the hereditary characters in them, it seems impossible to imagine the nature of such a supposed response. On the other hand, if we do not know the causes of mutation, the fact of their occurrence has been proved in so numerous individual cases that it can no longer be doubted, even by those who want to exclude the Oenotheras from the discussion.
“I shall be very glad to learn the results of your garden cultures. I should not wonder if your plants would behave just like the creosotbush of Tucson, and prefer better conditions to those which they enjoy (?) just-now. To me it seems that plants are found in those localities where they can better endure the circumstances than their competitors. But whether they really enjoy them, or would prefer more moisture and more fertile soils, and so on, is another question.”