Indusium cordate, fixed by the sinus. Wood Ferns. Aspidium.
Indusium hood-shaped, fixed centrally behind the sorus and arching over it, soon withering, often illusive. Fronds two to three pinnate, very graceful. Moisture-loving species. Bladder Ferns. Cystopteris.
Indusium star-shaped, of a few irregular segments fixed beneath the sorus, often obscure. Mostly small, rock-loving plants, usually rather chaffy, at least at the base, and growing in tufts. Woodsia.
Indusium cup-shaped, fixed beneath the sorus, supported by the tooth of a leaf; sporangia borne in an elevated, globular receptacle open at the top. Fronds finely cut. Hayscented Fern. Dennstædtia.
(3) Fruit-dots and indusium linear. (But see Athyrium.) Very long, nearly at right angles to the midrib, double; blade thick oblong-lanceolate, entire; heart-shaped at the base. Hart's Tongue. Scolopendrium.
Shorter and irregularly scattered on the under side of the frond, some parallel to the midrib, others oblique to it, and often in pairs or joined at the ends; blade tapering to a slender tip. Walking Fern. Camptosorus.
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.

[DESCRIPTIVE TEXT OF THE FERNS]

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 (Polypodiàceæ) with sixty species and several chief varieties. Then follow the flowering ferns (Osmundàceæ) with three species; the curly grass and climbing ferns (Schizæàceæ) with two species; the adder's tongue and grape ferns (Ophioglossàceæ) with seven species; and the filmy ferns (Hymenophyllàceæ) with one species.