The asexual generation. Perennial plants. The stem branches monopodially (often apparently dichotomously), and is thickly covered by small, simple, triangular or scale-like leaves. The leaves are spirally arranged in some species (Figs. [229], [230]), and in others, whose stem is compressed with unequal sides, opposite (Fig. [231]). The roots of Lycopodium are dichotomously branched.
The SPORANGIA in Lycopodium are situated singly at the base of the leaves, almost in their axils; they are reniform, unilocular and open like a mussel-shell by two valves (Fig. [230] h). The sporangia are developed from a group of surface cells. The archesporium is formed from one hypodermal cell (or perhaps a cell-row).
Fig. 231.—Lycopodium complanatum: a leaves on the edges of the stem; d leaves on the sides.
Fig. 232.—Lycopodium clavatum. A tetrahedral spore seen from above, where the three borders join; and a tetrad of bilateral spores, still lying in the mother-cell.
The fertile leaves are collected upon definite regions of the stem. They are either similar to the barren ones, and then the fertile portions of the stem pass gradually, without any break, into the barren portion (L. selago); or they differ from the barren leaves, and are then collected into special apical cones (Fig. [230] a). The SPORES are tetrahedral or bilateral (Fig. [232]).
About 100 species, chiefly tropical.
Five species of Lycopodium are found in Great Britain. L. clavatum and L. selago are common in mountainous districts. L. annotinum is common in the Highlands of Scotland. The other genus of the order is Phylloglossum, with one species, P. drummondi (Australia, Tasmania, and New Zealand), a small plant only a few centimetres high, with two tubers, and about eleven linear leaves at the base of the stem which is terminated by a cone of sporophylls.—Fossil Lycopodiaceæ in the Carboniferous period.
Officinal: “Lycopodium,” the spores of L. clavatum.