In the United Kingdom there is only one native species of Selaginella.
Selaginella spinosa. In this case the generic name is derived from the name Selago; actually the name means “a little Club Moss.” The specific name has reference to the tiny spines on the margins of the leaves. The Lesser Alpine Club Moss.
This plant is, of course, very distinct from the Lycopodium, in that it produces two kinds of spores. The Lesser Alpine Club Moss is a small plant with both prostrate and upright stems. The leaves are very tiny, and owing to their semi-transparent nature the whole plant is of a pale green colour. Some of the upright stems are barren, but a certain proportion bear the spore capsules in the axils of the small leaves. In the upper part of the cone occur the capsules containing the microspores, whilst in the lower portion are to be found the sporangia, each of which produces three or four megaspores.
The Lesser Alpine Club Moss is probably more common than is generally supposed, especially in the North of England. It grows in damp situations and is often very much mixed up with other herbage, so that it is easily overlooked. It is now necessary to describe the two or three curious little plants which are closely related to the Ferns and Club Mosses.
Isoëtes lacustris. In this case the generic name originates in two Greek words—isos, “equal,” and etos, “a year.” This has reference to the fact that the plant keeps its leaves all through the year and does not alter in appearance. The specific name lacustris is derived from the Latin word lacus, a lake, and is an allusion to the fact that the plant grows in such a situation. The Quillwort.
This is an interesting little plant which is entirely aquatic in its habits. The Quillwort has a tuberous root-stock, and from this arise a large number of dark green leaves, somewhat resembling quills in shape. These are about three or four inches in length, and when the plant is growing in quantity in some pool, it is often taken for a kind of grass. At the base of the leaves, partly protected by the sheathing, are to be found the spore capsules. These cases are of two kinds, those on the outermost rows of leaves containing the large spores, and those on the inner leaves being responsible for the small spores.
Isoëtes lacustris. The Quillwort.
The Quillwort is often abundant in mountain lakes in Scotland and the North of England. Owing to its habit of growth, however, the plant is usually unnoticed by the majority of people.
Another species of Quillwort—Isoëtes Hystrix—occurs in the Channel Islands, but it has not been found elsewhere in the United Kingdom.