[Illustration: The Rue Spleenwort. A. Ruta-muraria (Top, Lake Huron--Lower Left, Mt. Toby, Mass.--Lower Right, Vermont) (From Herbarium of Geo. E. Davenport)]
This tiny fern grows from small fissures in the limestone cliffs, and is rather rare in this country; but in Great Britain it is very common, growing everywhere on walls and ruins. From Mt. Toby, Mass., and Willoughby Mountain, Vt., to Michigan, Missouri, Kentucky and southward.
[B. THE LARGE SPLEENWORTS. Athýrium]
The following species, which are often two to three feet high and grow in rich soil, are quite different in appearance and habits from the small rock spleenworts just described. Some botanists have kept them in the genus Asplenium because their sori are usually rather straight or only slightly curved, but others are inclined to follow the practice of the British botanists and put them into a separate group under Athýrium. Nearly all agree that the lady fern, with its variously curved sori, should be placed here, and many others would place the silvery spleenwort in the same genus, partly because of its frequently doubled sori. In regard to the last member of the group, the narrow-leaved spleenwort, there is more doubt. The sori taken separately would place it with the Aspleniums, but considering its size, structure, habits of growth and all, it seems more closely allied to the two larger ferns than to the little rock species. We shall group the three together as the large spleenworts, or for the sake of being more definite adopt Clute's felicitous phrase.
THE LADY FERN AND ITS KIN
1. THE LADY FERNS
Fronds one to three feet high, broadly lanceolate, or ovate-oblong, tapering towards the apex, bipinnate. Pinnæ lanceolate, numerous. Pinnules oblong-lanceolate, cut-toothed or incised. Fruit-dots short, variously curved. Indusium delicate, often reniform, or shaped like a horseshoe, in some forms confluent at maturity.
Widely distributed, common and varying greatly in outline. The newer nomenclature separates the lady fern of our section into two distinct species, which should be carefully studied.[A]