On the Geographical Distribution of Ferns.

From the Latin of Alexander, Baron von Humboldt.

Paris, 1817.

IT will not escape the studious observer of the natural stations of plants, that in the cryptogamous class of vegetables, the Order of Ferns distinguishes itself from those of Mosses, Liverworts, and Mushrooms, in this particular, viz. that the latter have many species which are owned in common as well by the north of Europe as by the tropical regions of both the Old and New Continents, and not merely as peculiar to the mountains, but likewise as inhabitants of their plains; such are Funaria hygrometrica (twisting cord moss,) Dicranium glaucum (white fork moss,) Polytrichum juniperinum (juniper-leaved hair moss,) and the Lichens Verrucaria Perella, Sticta crocata, Parmelia perlata, &c. all which are found as well on the trees and rocks of the West Indian Islands, the chain of the Andes, the East Indies, and that part of New Holland which stretches towards the North, as in the Forests of Sweden and Great Britain.

While among ferns a far narrower range has been allotted to the species, for with very few exceptions those of the new and old continents, not only differ in the one from those in the other, but in the tropical regions are manifestly distinct from their co-ordinates of the temperate and frigid zones.

Phanogamous plants, are those in which the organs of fructification are apparent and determinate; cryptogamous plants, those where these are more or less clandestine and indeterminate; agamous plants, those in which those organs either are not present, or have not been detected. K

In tracing the native stations of the ferns, and the plan of their distribution over the face of the earth, I have ascertained that of the 1000 species that have been as yet observed, 760 belong to the torrid zone, and 240 to the temperate and frigid zones.

But when we speak generally of the number of these plants, the subject presents itself three ways; one, regarding the relative numbers of the species among themselves, another regarding their numbers in relation to the phaenogamous portion of vegetation, and a third in regard to the quantity each species may of itself exist in.

Thus Wahlenberg reckons 19 species of fern in Lapland, Hoffmann, 40 in Germany, Swartz, 103 in Jamaica, making the proportions of the frigid, temperate, and torrid zones, as they relate to each other in this point, as 1, 2, and 5. But the amount of phaenogamous plants in these regions is greatly disproportionate; for in Lapland there are 514 known species, and in Germany 1884, making the proportions 1:25 and 1:48.

Whether this relative disproportion increases towards the equator or not, is unknown to me; but if it were 1:50, and if the ferns have come incompletely within the view and observation of botanists as the phaenogamous portion of the vegetable creation, (which has hardly been the case,) the result would be, that 5000 phaenogamous species have been already discovered in Jamaica, and 23,000 in the whole of the tropical extent of America.

The degrees of abundance with which nature has sent forth particular species are manifestly various: at the extremity of Norway, on the shores of the frozen sea, ferns, although but few in species, cover nearly the whole face of the land.

Swartz, who attended diligently to ferns, has only recorded 764 phaenogamous plants in Jamaica.

In Michaux's Flora of North America 45 ferns and 1575 phaenogamous plants have been described.

The Isles of Bourbon and France comprehend 137 species of plants.

Of the 1000 species of ferns recorded by Willdenow, 470 grow in the old world; viz.

170 in the temperate and frigid zones, 300 within the tropics; and 530 grow in the New World, viz.

70 in the temperate and frigid zones, and 460 within the tropics.

I have elsewhere attempted to show, that if we represent the land within the tropics by = 1000, we are to allot it in the following proportions; to

Africa, .............. 461

America ............. 301

New Holland and the Islands in the Indian Sea, 124

Asia ............... 114

leaving the proportion which belongs to the New World in relation to that of the Old as 5 is to 7. So that if we did not know the New World to be of a more humid constitution with a more mountainous surface than the Old, and that the interior of Africa and New Holland have been far less explored than the regions that lie between the Orinoco and the river of the Amazons, we might be led to wonder why the portion of America, being considerably the least, should have by  1/3  the largest proportion of ferns.

I am fully aware that too much reliance must not be placed on the exactness of the amounts, since it has not been ascertained, what proportion of each of the various regions of the earth has been accurately explored; nor what proportion of the total of vegetation has escaped the notice of the botanist; nor whether all the different tribes of plants have been investigated with equal care.

But independent of these doubts, it is clear that the number of species cannot at all events be less than that which I computed.

Although the phaenogamous plants of tropical America are entirely different from the phaenogamous ones of the Old World, yet the northern portion of America has many in common with Europe and the North of Asia.

Whence it may be inferred, that at some period those continents have joined towards the North Pole; and it will be a matter of wonder, that so few European ferns are found in Canada, Pennsylvania, and California; for of such we do not hear of more than from 6 to 10 species, as for instance, Ophioglossum vulgatum, (common adder's-tongue,) Polypodium calcareum, (rigid three-branched polypody.) Aspidium thelypteris, (marsh shield-fern, or Lady-fern,) Acristatum, (lesser crested shieldfern) Pteris aquilina, (common brake,) &c.; but then Europe altogether does not contain more than 70 indigenous species of fern.

Towards the South Pole, the ferns, which grow at the extremities of the two continents, differ more than those of the northern temperate zone do from each other.

The only instances of any common to all the continent in those regions, that I am aware of, are Davallia pinnata, which grows in Chili and in the Philippine Islands; and Osmunda barbara, which grows in New Holland and at the Cape of Good Hope.

Hence it is the more strange that Aspidium aculeatum, (or common prickly shieldfern,) which is the only one among the ferns of the Old World that ranges through several of the zones, extending itself from England across Mount Atlas to the southernmost verge of Africa, should not have yet been met with in America.

According to Messrs. Forster and Brown, Botrychium Lunaria, (common moonwort) familiar in every part of Germany, covers, in company with the Phleum alpinum, (alpine cat's-tail-grass) of our country, every rock in Tierra del Fuego.

Hymenophyllum tunbridgense, (Tunbridge filmy-grass) grows in New Holland as well as in Ireland, Norway, and Italy.

The only instance of a species of the fern-tribe growing both in the Old and in the New continents, in the torrid as well as in the frigid zone, in a northern and a southern hemisphere, viz. in England, Jamaica, and the Isle of Bourbon, is the Adiantum Capillus Veneris, (true maiden-hair,) a plant which has been commemorated by Hippocrates, Theophrastus, and Dioscorides.

It has however been surmised by some that the germs of this fern have adhered to the filtering stones used aboard ships in long voyages, and been thus carried along with them and disseminated over the world.

It is not quite clear, that any fern has been found that is common to the tropical regions of both the New and Old Continents.

Authors have as yet only suggested three such instances, viz.

Aspidium punctulatum, A. coriaceum, and Asplenium monanthemum, which are said to be spontaneous in the West Indies, the Andes of Peru, Guinea, New Holland, and the Cape of Good Hope.

To these may be added Asplenium falcatum, and Blechnum caudatum, supposed to belong to South America and the Islands of Magindanao as well as Ceylon.

But I doubt whether the statements concerning these instances are so well authenticated, as those mentioned above of Hymenophyllum tunbridgense, and Botrychium Lunaria.

More than half of all the ferns yet observed belong to four genera only, viz.

to Polypodium, (Polypody,) Aspidium, (Shield-fern,) Pteris, (Brake,) and Asplenium, (Spleenwort.) Some types among them seem confined almost entirely to tropical lands, as Meniscium, Anemia, Hydroglossum, Mertensia, and Schizea:

but all the generic types of the northern temperate zone are found likewise between the tropics.

The New World alone has no genus of the Fern-tribe peculiar to itself, although many of its phaenogamous genera are so; for example, Cactus, Calceolaria, Alstroemeria, Bromelia, and others.

As for the fern-types Polybotrya, Pleopeltis, and Marattia, so few species of them have been found, that it is highly probable other congeners will be detected in our own continent, so that they can hardly be relied on as exceptions.

Ferns, which in the northern frigid zone grow along the ground in the shade, in the tropical regions, shoot up to the dimensions of trees, vying with the palms themselves in stature and comeliness.

These tree-ferns constitute a principal ornament of the torrid zone, giving that peculiar character to the spots where they grow, which strikes so forcibly the European stranger by its novelty.

The Greek and Roman writers who have treated of plants, mention in several places, that many which in Europe creep along the ground, in hotter climates become trees, making it the more remarkable, that none should speak of a tree-fern; particularly as Megasthenes, Aristobulus, and Nearchus, recount among the wonders of Indian and Ethiopian lands, that there are trees having leaves as large as a shield, a fig-tree that takes root at the ends of its branches, and palms too high for the flight of an arrow to pass over.

Theophrastus, Dioscorides, and Pliny, who has trodden over again the ground of the two first, mention only eight or ten species of ferns, none above a yard high.

And when a certain sort of fern brought from India is noticed, as being known to the philosopher Eresius, no observation is offered concerning the stature of the stem, attention being only bestowed on certain medicinal qualities imputed to the plant.

So that tree-ferns must have been left unnoticed by the Romans and Greeks, either because in that portion of India, which the arms of Alexander had opened to them, or in Ethiopia and Lybia, which they visited in the view of commerce, none are to be found; or because their writers, as was usual in former times, left unnoticed all plants which did not recommend themselves to their attention by the fruit they bore, or the fragrance of their wood, or their medicinal virtues.

Oviedo, the Spaniard, in his history of the West Indies, is the first who mentions a tree-fern; for the Filix arborea of Tragus is nothing more than a variety of our common forked spleenwort, transplanted into a more fertile land.

So late as the time of Linnaeus scarcely 4 sorts of tree-fern were known, and about 15 sorts of palms; at present we are acquainted with 25 of the former, and 100 of the latter.

The tree-ferns of America are, Cyathea speciosa, C. arborea, C. Serra, C. muricata, C. multiflora, C. villosa, C. aspera, Pteris aculeata, P. villosa, Meniscium arboreum, Aspidium caducum, A. procerum, A. rostratum, Asplenium arboreum, caet.

Of New Holland and the Islands of the Indian Sea; Cyathea affinis, C. medullaris, C. dealbata, C. extensa, Dicksonia squarrosa, D. antarctica, caet.

Of Southern Africa, and the Islands of France and Bourbon.

Cyathea excelsa, C. glauca, C. riparia, caet.

The tree-ferns of the East Indies, Cochinchina, the Island of Madagascar, and the Cape of Good Hope have not yet been accurately described.

I have not included amongst the arborescent species, Aspidium Arbuscula, Lomaria Boryana, Polypodium rhizocaule, P. pruinatum, Pteris marginata, &c. because they are either climbers, or else shrubby or caulescent plants, with stems not more than three or four feet high.

Of the five new species of tree-ferns observed by M.

Bonpland and myself, Cyathea speciosa is the one which makes the finest appearance, and has a stem 25 feet high.

The C. excelsa of the Isle of Bourbon is said by Messrs.

Du Petit Thouars and Bory St. Vincent to grow to the same height.

In general, the tropical plants are further advanced towards the South Pole than towards the North Pole, a fact which seems inconsistent with the received opinion of the cold being greater in the Southern Hemisphere.

In North America and New Spain, the tree-ferns hardly ever grow beyond the limits of the tropic of Cancer, while only one species of palm (Chamaerops Palmetto) advances to Carolina, or the latitude of 37°.

In the Southern Hemisphere, on the other hand, Dicksonia antarctica, described by Labillardiere as having a stem near 20 feet high, grows in Van Diemen's Island; nay, another species of Dicksonia has been found at Dusky Bay in New Zealand, in the 46th degree of southern latitude, where in a parallel which corresponds with that of Lyons, the trees swarm with Epidendra and Dendrobia, vegetable parasites, which constitute the most graceful ornaments of the tropical Flora.

Phaenomena, which excite the more wonder, when we find from the observations of the celebrated navigators Cook, Entrecasteaux, and Flinders, that the mean annual temperature of this zone is scarcely equal to 12,5 of the centigrade thermometer.

But the great expanse of water in the Southern Hemisphere cools the heat in summer and assuages the cold in winter; so that in the 52d and 53d degrees of southern latitude, corresponding to that of Berlin in our hemisphere, the snow melts nearly every day of the winter, and the centigrade thermometer very seldom rises to 11° in the months of January and December, the hot summer months of these regions.

Even in the 42d and 43d degrees of Southern latitude, owing to the currents of wind that blow from the South Pole, the summers are hardly hotter than at the sides of the mountains of Switzerland:

these summers, on the other hand, are succeeded by winters even milder than those of Rome.

Labillardiere never observed the centigrade thermometer in Van Diemen's Island rise higher at mid-day than 15-17°,5 in the months of January and February; and Cook in the same parallel, during July, a winter month of those regions; never found the degree of cold below 8° of the centigrade thermometer.

In tropical America, as I have shown in another work, the herbaceous ferns grow in all parts, from the border of the sea, and from the plains, up to the heights of the Andes, although but little below the limits of eternal snow.

There are certain species peculiar to certain elevations, and each in its zone is unable to transgress that boundary which has been allotted to it.

Thus in the mountains of Peru and New Spain, Cheilanthes marginatus, Acrostichum muscosum, and Hemionitis rufa, grow between the elevations of 1200 and 1600 fathoms: in the same way the Pteris crispa, (rock-brake or curled stonefern) grows on Mount St. Gothard from above the region of Pines up to the elevation of 1,100 fathoms; and in Lapland, near Enontekies, to that of 300 fathoms; so that in Switzerland, its highest station is scarcely 280 fathoms removed from the limits of eternal snow, and in the North of Norway scarcely 100 fathoms.

Polypodium hyperboreum, (hairy alpine polypody) in latitude 68° advances still higher, to beyond Betula nana, (dwarf birch) Draba alpina (mountain whitlow grass) and Campanula uniflora, (one-flowered bell-flower.)

I have elsewhere explained myself on the subject of the reason why plants approach nearer to the boundary of eternal snow towards the North Pole, than they do in the torrid zone.

In the kingdom of Quito, M.

Bonpland and myself saw mountain-ferns reaching into the elevated plain which engirds Mount Antisana and along the sides of the Rucupichincha in the valley of Verdecuchu, both which spots are 2100 fathoms above the level of the sea; and also other herbaceous ferns on Mount Chimborazo, growing on porphyritic rock, as high up as 2300 fathoms.

But at heights so great, where the cold is so severe, as well as in parched unshaded plains and spots, the quantity of ferns is plainly perceived to diminish from the want of moisture.

Their main body is stationed in the temperate and sub-frigid zones, between the elevations of 300 and 1200 fathoms.

Tree-ferns in some regions occasionally grow down to the edge of the sea, and on lowlands in shady spots; but in those parts of tropical America where M.

Bonpland and myself passed five years, they occupy a peculiar zone, in which the temperature is between 18 and 22 degrees of the centigrade thermometer.

A delightful region, where vernal breezes prevail almost the year through, and which lies between the elevations of 400 and 800 fathoms from the level of the sea: though they sometimes descend as low as to the height of 200 fathoms.

This zone is called by the natives in the Spanish dialect, tierra templada de los helechos, the temperate land of the ferns.

The chief part of the tree-ferns we met with, was in New Andalusia, near the Convent of Caripa, and in New Granada near Ibague, Guaduas and Icononzo, and in the valleys of Peru between Loxa and the river of the Amazons also in New Spain near Xalapa.

The region of fern-trees is not far from that of the Cinchonas, or bark-trees; for we find Cinchona oblongifolia and C. multiflora, however fond they are of heat, mingling themselves with the tree-ferns in the Andes of Peru, and of the mountains of Quito and New Granada.

In New Spain they grow in company with the oaks* of that country; a strange association in the eye of the European.