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Ferns. The plants included under this name comprise an entire order, made up of several
distinct families. They include plants varying in size from a hair- like creeping stem
bearing a few simple, moss-like leaves, to tall trees 80 or more feet in height, with a stem
or trunk nearly a foot in diameter. Singularly enough, the extremes in size are both found
in tropical regions, in which most of the species abound. Most of the ordinary native
species, as well as the larger part of those in cultivation, consist of an erect underground
stem or rootstock with leaves, often called fronds, clustered in dense crowns, or in the
cases of creeping stems with scattered leaves. In gardening parlance, other plants are
sometimes called ferns, as species of lycopodium and selaginella, as well as oa em Asparagus
plumosus.
In the life of an individual fern plant, two distinct phases occur, represented by two
separate and unlike plants. The ordinary fern plant represents the asexual phase of growth
(sporophyte), producing its spores normally in spore-cases, which are borne in masses on the
back or margin of the leaf, or in. a few cases are grouped in spikes or panicles, or in rare
cases spread in a layer over the entire under surface of the leaf. The sexual stage
(gamelophyte) develops from the germinating spore, and consists of a tiny usually scale-like
green heart- shaped prothallus, which bears the sex- organs (archegonia, female, and
antheridia, male) on the under surface. After fertilization in the archegonium, the egg
develops directly into a young fern plant. Many ferns also propagate vegetatively by runners
or offsets, by bulblet-like buds, and in certain species the tips of the leaves bend over
and take root, as in our common walking-leaf (Camptosorus, which see).
Ferns frequently hybridize. The crossing takes place naturally in the prothallium stage.
They are not crossed by hand, as are the seed-plants, but from the accidental mixing when
prothallia of allied species are growing together. It is a hybrid between two native
species; it has been found in the wild in several parts of New England.
Great diversity has existed in the matter of the separation of the ferns into genera.
Hooker, relying mainly on artificial characters drawn largely from the sorus, recognized
about seventy genera only, many of them heterogeneous groups of plants with little
resemblance in structure, habit or natural affinities. John Smith, relying on stem
characters, Presl on variation in venation and habit,Fee, Moore,and others, have recognized
a much greater number of genera, ranging from 150 to 250, or even more. In the very unequal
treatment by Diels in Die Naturlichen Pflanzenfamilien (Engler & Prantl), some 120 genera
are recognized. A somewhat similar difference prevails in regard to the number of species.
The Synopsis Filicum of Hooker and Baker (1874), supplemented by Baker's New Ferns (1892),
recognizes some 2,700 species. It is the too prevailing tendency in this work (1) to fail to
recognize many valid species which have been described by German and French botanists, and
(2) to mass under one name very diverse groups of species from distant quarters of the world
from 8 to 10 species not infrequently appearing as a single so-called "variable species."
The most recent book dealing with the whole order of ferns, the Index Filicium by Carl
Christensen, recognizes approximately 150 genera and 6,000 species, and this number is
continually increased as the result of further tropical exploration and more careful study.
New forms are constantly coming in from the less-explored parts of the world, and within the
last few years several new species have been described from the United States, including
some from the better-known parts. Of this number some 200 species are in occasional
cultivation in America, but the species that form the bulk of the fern trade do not exceed
two dozen. In Europe several hundred species have long been in cultivation. Most of the
species thrive best in the mountain regions of the tropics, the mountains of Jamaica and
Java having nearly 600 species each, and the Andes also a large number. About 165 species
are native in the temperate United States, representing some thirty-five genera; our native
species are so widely distributed that usually not more than twenty-five to fifty will be
found within the limits of one state, and the common species of the best locality do not
number more than twenty. Recent explorations in southern Florida have discovered in that
state the presence of a considerable number of West Indian species not found elsewhere in
the United States.
The ferns are commonly classified as part of a group of spore-bearing plants, with vascular
(woody) tissue in stem and leaves; this group is technically known as the Pteridophytes, and
is ordinarily divided into three orders; viz., the Equisetales, including the horsetails'
and scouring rushes; the Lycopodiales, including the selaginellas and the club mosses, or
ground pines; and the Filicales, including the true ferns and their nearer allies. The
Lycopodiales and Equi- setales are really not as closely related to ferns as this grouping
would indicate.
It should be noted that neither the family nor the generic limitations are in a settled
condition. The researches of Bower, Lang, Jeffrey, and others have resulted in some changes
of classification which are not included below because they are not complete enough. Their
conclusions are undoubtedly correct but are not at present usable.
The families of the order Filicales may be distinguished as follows:
1. Ophioglossaceae. Adder's-Tongue Ferns. Herbaceous small ferns with the sporangia borne in
spikes or panicles on highly modified divisions of the large fleshy foliage lvs.; prothallium
tuberous, subterranean, without chlorophyll.
2. Marattiaceae. Coarse ferns with large fleshy sporangia on the under surface of the lf.,
arranged in circular or boat-shaped receptacles; prothallium above ground, green.
3. Hymenophyllaceae. Filmy ferns. Sporangia attached to a thread-like receptacle arising in
a cup at the end of the lf.: ring complete, horizontal or oblique.
4. Osmundaceae. Flowering ferns. Coarse swamp ferns developing copious green spores early in
the season: sporangia in panicles at the apex or middle of the lf. or on separate lvs.
5. Schizaeaceae. Upright or climbing ferns with ovate sporangia, which open vertically.
6. Gleicheniaceae. Terrestrial ferns with lvs. of firm texture and usually of indeterminate
growth: sporangia opening vertically, in clusters of 3-6.
7. Ceratopteridaceae. Aquatic ferns with succulent foliage: sporangia very large, scattered,
with a broad ring: lvs. of 2 sorts, the sterile usually floating.
8. Cyatheaceae. Mostly tree ferns with sessile or short-stalked sporangia in conspicuous
receptacles, opening obliquely.
9. Polypodiaceae. Ferns with stalked sporangia, which burst transversely: sori covered with
a membranous indusium or sometimes naked. This family contains three-fourths of all the
ferns.
10. Marsiliaceae. Small plants rooting in mud, the lvs. either quadrifoliate or reduced to
mere filamentous petioles: sporangia borne in oval conceptacles on the leaf-stalks. Often
aquatic, with the leaves floating on the surface of water in pools or lakes.
11. Salviniaceae. Small or minute plants with the aspect of liverworts, floating on the
surface of pools: sporangia in mostly spherical conceptacles.
The literature on the ferns is very extensive, since they have ever been attractive plants
in cultivation. Many of the species have been illustrated in elaborate treatises by Schkuhr,
Kunze, Hooker, Greville, Blume, Fee, Mettenius, Moore, and others. Our native species have
been illustrated in the two quarto volumes of D. C. Eaton, "The Ferns of North America." A
valuable summary of the more common fern species is found in Dr. Christ's "Die Farnkrauter
der Erde" (1897), and a recent structural and morphological treatment is by Sadebeck, in
Engler & Prantl: "Die Naturlichen Pflanzenfamilien." Schneider's "Book of Choice Ferns" is
the most complete treatise on the species under cultivation. A useful American horticultural
manual is Robinson's "Ferns in Their Homes and Ours." An excellent little handbook for the
wild species of this country is Underwood's "Native Ferns and Their Allies."
L. M. Underwood.
R. C. Benedict.
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{{dablink|This article is about the family of pteridophyte plants. For the environmental organisation, see [[FERN (NGO)]]. For the letter of the [[Ogham]] alphabet, see [[Fern (letter)]]. }}
{{dablink|This article is about the family of pteridophyte plants. For the environmental organisation, see [[FERN (NGO)]]. For the letter of the [[Ogham]] alphabet, see [[Fern (letter)]]. }}
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