This genus differs from the last in its reniform indusium, which is attached by the sinus. The sori are either dorsal or terminal on the free venules in the British species. As defined by Hooker and Baker, this genus comprises upwards of 200 species. The name is from 10 Nephrodium Lastrea 502 a kidney, the shape of the indusium.

1. N. Filix-mas, syn. Lastrea Filix-mas. Male Fern. - A very common British Fern with bipinnate tufted fronds from 1 to 3 feet long, springing from a short thick rootstock, sometimes forming a short stem above ground. Stipes short. Pinnules oblong, more or less toothed. Sori large, in one row on each side of the costa. There are several varieties, differing in the size and division of the frond and the quantity of chaffy scales on the stipes and rachis. N. Borreri, N. abbreviation, N. dffine, and N. cristatum, of Swartz, not of Richard, are forms of this species, in addition to which there are several crested and proliferous varieties in cultivation. A widely-dispersed species. N. cristatum differs from the foregoing in its flat, not convex indusium, and in the broad base of the pinnules; and N, rigidum in its mucronate rigid pinnules. Both are comparatively rare in Britain.

2. N. spinulosum, including N. dilatatum, etc. - This is another common species, usually affecting moist shady situations. It is a very variable plant in its extreme forms. The fronds are rather flaccid, dark green, bi- or tri-pinnate, on long-slender stipes, and usually somewhat deltoid in outline. Pinnules lobed to the rachis, furnished with awned teeth. A native of Europe, Asia, North America, and North and South Africa.

N. cemulum has a more triangular and divided concave frond, smelling strongly of hay.

3. A. Thelypteris. Marsh Fern. - This is a delicate species with creeping rootstocks, lanceolate pinnate fronds about a foot or 18 inches, or even more high; pinnae deeply pinnatifid; pinnules entire. Stipes equalling or exceeding the leafy part of the frond, very slender and nearly or quite naked. It grows in marshy and boggy places, and the fronds are only of short duration. Widely distributed.

4. N. Oreopteris, syn. N. montanum. Sweet Mountain Fern. - A handsome mountain species with tufted lanceolate pinnate fronds, pinnae pinnatifid, glandular beneath, the lower more distant and gradually smaller; pinnules entire. Stipes short, scaly. A native of Europe and Western Asia.

There are several handsome Japanese species of this genus belonging to the section Lastrea, as N. atratum, N, opacwm, and N. erythrosorum.