Growth Patterns of Five Species of Lycopodium

Abstract

Descriptions of the type and rates of growth of the lycopods have not been included in several recent studies of Lycopodium (Cardillo, 1970; Kukkonen, 1967; Bierhorst, 1971; Wilce, 1965). Wilce seems to have given the most attention to periodicity, for she says, arborescent and usually tufted species, determination of the age of the main upright axis is a simple matter of counting the number of seasonal 'leaf rings.' These mark the retardation or cessation of growth at the end of each season; with their small, crowded leaves, they might be compared to an angiosperm bud, but with the difference that the leaves of the lycopodiaceous 'bud' are persistent. (However, she did not report observing annual leaf rings on the rhizome of L. flabelliforme.) Colonies of five species of Lycopodium (L. lucidulum Michx., L. annotinum L., L. flabelliforme (Fern.) Blanch., L. clavatum L., and L. obscurum L.) growing at the Harvard Forest, Petersham, in central Massachusetts, were examined to determine their growth patterns and growth rates. Descriptions of the arrangement of the aerial shoots and rhizomes were made in the field. Measurements of annual growth of the aerial shoots and rhizomes were made in the laboratory on fresh specimens brought in from the field. The annual growth of the rhizomes of L. flabelliforme, L. clavatum, and L. annotinum was determined by locating the distinct microphyll compressions on the rhizome where the rhizome tip slowed down and then ceased growing in the fall and winter. Annual growth of aerial shoots can be determined in all species by noting the microphyll compressions on the shoot and branchlet axes. My observation that there are annual, externally visible microphyll compressions on the rhizomes of L. annotinum, L. clavatum, and L. flabelliforme, seems to be an original one. In L. annotinum the actively growing rhizome has straight microphylls, which are 5 mm long and 0.8 mm wide, spaced 13 mm apart. In late fall, the curved microphylls, which are about 7 mm long and 0.7 mm wide, are spaced 5 mm apart. In L. clavatum the actively growing rhizome has microphylls which are about 4 mm long and 0.8 mm wide at the base, spaced about 8 mm apart. In late fall the microphylls, which become longer and narrower (to 8 mm long and 0.5 mm wide), are spaced about 1.5 mm apart. In L. flabelliforme the shape of the microphylls does not change, but during active growth the rhizome microphylls are about 16 mm apart, whereas they are only 2 mm apart toward the end of the season. Lycopodium annotinum, L. clavatum, and L. flabelliforme have well-differentiated strobili and grow by a superficial rhizome just below the litter. Lycopodium annotinum has a sessile strobilus and leaves with aristate tips. Lycopodium