| 3. Fruit in lines on the margin of the pinnules; under surface of the fronds covered with whitish powder. Cloak Ferns. Notholæna. |
B. INDUSIUM PRESENT
| 1. Sori on the edge of a pinnule terminating a vein; sporangia at the base of a long, bristle-like receptacle surrounded by a cup-shaped indusium. Filmy Fern. Trichomanes. |
| 2. Indusium formed by the reflexed margin of the pinnules. (1) Sporangia on a continuous line; fronds large, ternate; indusium narrow. Bracken. Brake. Pteris. |
| (2) Sporangia in oblong sori under a reflexed tooth of a pinnule; indusium broad; rachis dark and shining. Maidenhair. Adiantum. |
| (3) Sori in roundish or elongated masses. Indusium broad, nearly continuous, fronds mostly smooth, somewhat leathery, pinnate. Rock species. Cliff brakes. Pellæa. |
| Indusium narrow, seldom continuous, formed by the margin of separate lobes or of the whole pinnules; often inconspicuous, fronds usually hairy. Lip Ferns. Cheilanthes. |
| Indusium of the reflexed edges, at first reaching to the midrib, or nearly so; later opening out nearly flat; fruiting pinnules pod-like; sterile fronds broad. Rock brakes. Cryptogramma. |
| 3. Indusium never formed of the margin of the frond. Sori various. (1) Fruit-dots oblong, parallel with the midrib, somewhat sunken in the tissues of the frond. Water-loving species. Chain Ferns. Woodwardia. |
| (2) Fruit-dots and indusium roundish. Indusium shield-shaped, fixed by the center. Evergreen glossy ferns in rocky woods. Shield Ferns. Polystichum. |