Undulate Atrichum Moss

Description

This is one of our most robust and distinctive acrocarpous mosses and soon becomes familiar to beginners. It is a loosely tufted, moderately robust species that can form extensive patches. These tend to be dark green, but are yellower when well-lit. Individual stems are erect, unbranched, and grow to 7 cm, with long, narrow, pointed leaves up to 1 cm long. Each leaf is distinctly transversely undulate when moist, and strongly crisped when dry. The leaf margins have paired teeth from near the base, and the back is rough, with numerous small teeth. The nerve ends in the leaf tip. Capsules are frequent in the common var. undulatum. The inclined, cylindrical capsule is 3-4 mm long with a lid and beak of similar length to the capsule. It is borne on a 2-4 cm long reddish seta. There are 32 peristome teeth and the mouth of the capsule is closed by a delicate drumskin-like membrane (as in other Atrichum and Polytrichum species, and other relatives). The very rare var. gracilisetum has male organs just below the female, whereas in the common var. undulatum male and female organs are borne on different branches. Var. gracilisetum also differs from var. undulatum in having yellow setae and a straighter capsule. It usually produces several capsules per shoot, and these remain in situ, so old fruits appear lateral on growing stems.