This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Rhizome tufted, or slightly elongated. Fronds simple or compound. Sori on the veins, linear or oblong. Indusium linear, membranous, attached to the vein arid opening inwards. A very large genus, including nearly 300 species, and represented in all except the very coldest countries. The name is from a, privative, and spleen, in allusion to the reputed medicinal properties of some species.
§ 1. Euasplenium. - Indusium straight, narrow; margin entire or erose. Frond not scaly beneath; veins free.
1. A. Ruta-muraria. Wall Rue. - This is the little tufted Fern so common on walls and rocks, with irregularly bipinnate fronds and cuneate pinnules.
A. Germanicum, syn. A. alternifolium, and A. septen-triondle, are allied species of more erect growth, and fronds with narrow, linear segments. They are both rare in Britain.
2. A. Trichomanes. - A dwarf tufted Fern with linear pinnate fronds 4 to 8 inches long, and numerous oblong dark green pinnules. Stipes dark brown, shining. Sori oblique. Frequent in Britain on walls, banks, etc, and one of the most attractive of small hardy species. Distribution general in the north temperate zone. A. viride differs in its smaller size and green rachis. It is found in the mountains of Wales and Scotland.
3. A. marinum. - This is a stout tufted species from 6 inches to afoot high, with pinnate coriaceous oblong-lanceolate fronds, and oblong crenate pinnules. It grows on rocks in the vicinity of the sea, chiefly in the south-west. It occurs in South-western Europe, North Africa, and North America.
4. A. Adiantum-nigrum. - This is perhaps the commonest of the native species of this section. It has bi- or tripinnate triangular coriaceous fronds 6 to 12 inches long, with narrow pinnatifid and toothed pinnules. Stipes slender, naked. It is found throughout Europe, North Africa, and Western Asia, growing on dry banks and rocks.
A. lanceolatum is very near the last, but the fronds are membranous, and the pinnules narrower and more acute. It is rare in Britain, and only found in Wales and Western England.
§ 2. Ceterach. - Frond covered with chaffy scales beneath; veins anastomosing.
5. A. Ceterach, syn. Ceterach offcinarum. - Fronds about 6 inches long, pinnatifid; pinnules alternate, rounded. This Fern is readily known from all other indigenous species by its linear-lanceolate coriaceous fronds, which are densely clothed beneath with rusty chaffy scales, effectually concealing the fructification. It is usually found on walls and dry banks. It is a native of Europe, Western Asia, and North Africa.
§ 3. Athyrium. - Indusium oblong or reniform, fringed at the margin. Veins free.
6. A. Filix-foemina. Lady Fern. - A very beautiful species with delicate bright green bi- or tripinnate fronds from 1 to 4 feet high; pinnules small, crowded, sessile, acuminate. Stipes stout, densely dotted with chaffy scales at the base. The numerous varieties in cultivation differ in size, aspect, and in the cutting and lobing of the fronds to a degree almost in-credible, and include some of the most elegant and graceful of hardy Ferns. A. Rhaeticum with bipinnate narrow fronds, and A. inclsum with very large tripinnate fronds, are two of the commonest wild forms. Widely distributed in the northern hemisphere.