This section is from the book "The Native Flowers And Ferns Of The United States ", by Thomas Meehan. Also available from Amazon: The Native Flowers and Ferns of the United States in Their Botanical, Horticultural, And Popular Aspects.
Fronds leathery, evergreen, veins obscure, sometimes reticulating near the margin, smooth and green above, pinnately parted; the divisions oblong, obtuse, entire. The frond beneath, as well as the stipe, thickly beset with peltate, chaffy scales ; fruit dots near the margin. (See Chapman's Flora of the Southern United States.')
ERNS which grow on trees are confined to a very few species in the United States, and of all of them the pretty little species, called Polypodium incanum, is perhaps the most frequently found here. In Europe, at least in England, the most common fern found growing on trees is an allied species, P. vulgare, a native also of the United States, where, however, it is more often found in the clefts and on the ledges of shaded rocks than on trees. It is interesting to note that the species now illustrated, which, as we have just remarked, is allied to P. vulgarc, seems to have advanced from the south towards the north, while P. vulgare has travelled towards the south, so that the advancing colonies have met and intermingled in the northern parts of the Southern States. And here we find that, while in the centre of its range, and where we may suppose was its original home, the Polypodium incanum is mostly found on trees, when it meets its northern friend it takes to the same habit of often growing: on rocks. As so few ferns in our district grow on trees, as compared with those which we might suppose to be able to adapt themselves to such situations, it is more than probable that, in the order of evolution, ferns growing on trees epiphytal ferns - are a comparatively late class in the sequence of creative time. Some of the earlier botanists regarded this species as a "parasite," but many modern ones do not regard it as even an epiphyte, in the sense of attaching itself to trees, believing that it grows only among moss or other decaying material which is collected on the trunks and branches. In Mississippi, where I have seen it abundantly on oaks, it was always associated with moss, as is the specimen here illustrated, which was kindly cut for us from the roof of a house in South Carolina, by Dr. Mellichamp. But in Louisiana I have seen it running up the straight trunks of trees, firmly attached to the bark, without a trace of moss. In this situation, the fronds dry and curl up during the hot weather, the whole plant looking brown and dead; but when the spring rains come in April, the curled leaves unfold, and the plant resumes growth where it stopped the preceding year.
In regard to its geographical range, I have been furnished with some very interesting facts by Mr. J. H. Redfield, who has followed its history closely. Inhabiting all parts of tropical America and the islands of the Carribean Sea, the Polypodium incamim enters the United States by the way of Mexico, through Texas. The Cumberland Mountains appear to have checked its direct progress, for it seems to have no desire to get up in the cold; it therefore branched off, part of the little army marching round to the west and north, going up the line of the Mississippi, and then taking the course of the Ohio, so as to just reach that state; the other winding round to the east, and then going north along the Seaboard States, reaching as far as the Dismal Swamp and the Natural Bridge in its northern march. In this way the great ridges of mountains form an immense barrier between the eastern and western colonies.
No attempts that we know of have been made to cultivate it in the open air further north, and in view of the great distance from its original home, it would not probably succeed; but, fastened to blocks of wood and moss, so that it could be moved to rooms, cellars, or green-houses in winter, after hanging out under trees in the summer, it would make a very interesting object to grow.
The common name of this family of ferns is "Polypody," from its botanical name as given by Linnaeus, Polypodium, Greek words signifying "many feet." This is the ancient name of some fern, and was adopted by the earlier botanists as probably belonging to the genus under consideration, to which the name seemed applicable on account of the many "little feet" which the numerous creeping root-stocks of the original species possessed. "Incamim" is Latin for hoary, the leaves when dry exhibiting the scaly under-surfaces, of a dull, silvery color. The "Hoary Polypody" would be a good popular name for this fern.
Our plate shows the plant as usually seen, though the fronds are described by Chapman as being sometimes six inches long. We give an enlarged portion of a pinnule, so that the great beauty of the peltate scales may be readily seen. These little scales give a peculiar interest to this species. The fronds themselves are not, to our taste, as pretty as those of its northern sister, Polypodium vulgare, which, with its abundant masses of yellow sporangia, all in very regular order, seems to require no further ornamentation. This species does not appear to have the power of producing spores as freely; and, if we may speak of plants as the poets speak, suppose it was annoyed at the superior beauty of the other, and the effort to rival it resulted in these pretty scales ! Darwin, in a like fanciful vein, pictures the ice-plant, " With pellucid studs the ice flower gems His rimy foliage and his candied stems," speaking as if he were describing a not very young gentleman who depended somewhat on jewelry to atone for departed charms. He would, doubtless, regard this effort by our little fern as a similar attempt by one of the other sex! In ferns there are two distinct modes of growth. In the one, the fronds push up in a direct way; in the other, they are circinate, or unfold as in the unrolling of a coil. This latter mode is a very-beautiful form of growth, and the artist has happily caught our specimen in the unfolding act.
1. A section of the scaly rhizome, with fronds showing the upper and lower surfaces.
2. Section of pinnule, enlarged three times, and showing the sori and scales.