Short, straight, mostly oblique to the midrib. Indusium rather narrow, opening toward the midrib, fronds lobed or variously divided. Spleenworts. Asplenium.
Short, indusium usually more or less curved and frequently
crossing a vein.
The large spleenworts including Lady Fern. Athyrium.
In this manual our native ferns are grouped scientifically under five distinct families. By far the largest of these groups, and the first to be treated, is that of the real ferns (Polypodiaceae) with sixty species and several chief varieties. Then follow the flowering ferns (Osmundaceae) with three species; the curly grass and climbing ferns (Schizaeaceae) with two species; the adder’s tongue and grape ferns (Ophioglossaceae) with seven species; and the filmy ferns (Hymenophyllaceae) with one species.
Corresponding with these five families, the sporangia or spore cases of ferns have five quite distinct forms on which the families are founded.
[Illustration: Fig. 1]
[Illustration: Fig. 2]
[Illustration: Fig. 3]
[Illustration: Fig. 4]
1. The Fern Family proper (Polypodiaceae) has the spore cases stalked and bound by a vertical, elastic ring (Fig. 1). The clusters of fruit-dots containing the spore cases may be open and naked as in polypody (Fig. 2), or covered by an indusium, as in the shield ferns (Fig. 3).
2. The Royal Fern Family (Osmunda) has the spore cases stalked with only a rudimentary ring on one side, which opens longitudinally (Fig. 4).
3. The Climbing Fern Family (Lygodium, Schizaea) has the spore cases sessile in rows; they are small, nut-like bodies with the elastic ring around the upper portion (Fig. 5).
[Footnote 1: These figures are enlarged.]
4. The Adder’s Tongue Family (Ophioglossum, Botrychium) has simple spore cases without a ring, and discharges its spores through a transverse slit (Fig. 6).
5. The Filmy Fern Family (Trichomanes) has the spore cases along a bristle-like receptacle and surrounded by an urn-shaped, slightly two-lipped involucre; ring transverse and opening vertically (Fig. 7).
[Illustration: Fig. 5]
[Illustration: Fig. 6]
[Illustration: Fig. 7]
Green, leafy plants whose spores are borne in spore-cases (sporangia), which are collected in dots or clusters (fruit-dots or sori) on the back of the frond or form lines along the edge of its divisions. Sporangia surrounded by vertical, elastic rings bursting transversely and scattering the spores. Fruit-dots (sori) often covered, at least when young, by a membrane called the indusium. Spores brown.