The Status of Hylocomium splendens var. tenue

Abstract

it as Hylocomium splendens var. tenue Sharp (1933). In the recent checklist of North American mosses (Crum, Steere & Anderson, 1965), we erroneously referred the name to the synonymy of H. splendens var. gracilius (Boul.) Husn. - an unimportant growth form of the species, somewhat smaller, more compact, and less obviously proliferous than usual, and quite unlike the variety tenue. The variety tenue scarcely resembles Hylocomium splendens in size or aspect. It is completely lacking in paraphyllia (Fig. 8-10), a conspicuous and essential feature of Hylocomium, and there is little or no differentiation of stem and branch leaves (Fig. 1) other than a gradation in size (Fig. 7). To be sure, the leaves are remarkably similar to those of the ultimate branches of Hylocomium splendens in shape (Fig. 3-5), areolation (Fig. 2), and dorsal papillosity (Fig. 10). In Hylocomium splendens, however, the leaves of the ultimate branches show some significant differences: they are more concave with the upper margins incurved, the lower margins are not recurved, and the spiculose papillae at the back of the leaf cells are scattered and few rather than consistently present. In trying to place this moss taxonomically, we were led to a consideration of Pterigynandrum for a number of reasons including a similar size, general appearance, leaf shape, apex, decurrencies, and margins (serrulate in the upper half, narrowly recurved below the middle) (Fig. 6), small and relatively few quadrate alar cells, and, above all, the dorsal papillae caused by thickened and projecting cell ends. The thin-walled, relatively elongate leaf cells and small papillae obscured an obvious relationship to Pterigynandrum and indeed made Dixon's suggestion of an affinity to Hylocomium almost inspirational. However, a detailed study of Pterigynandrum filiforme Hedw. in all its variations has led us to the conclusion that Hylocomium splendens var. tenue is a species of Pterigynandrum differing from P. fiiforme most strikingly in having somewhat longer, much thinner-walled cells with much smaller papillae at back. A lack of pseudoparaphyllia (few and different to demonstrate in P. filiforme), as well as less concave and less crowded leaves with a more glossy appearance associated with smaller leaf papillae, fewer quadrate alar cells, and longer costae, helps to differentiate the species. No axillary brood bodies, so characteristic of the many expressions of P. filiforme (Crum, 1953), were found.