Mnium hornum

Swan's-neck Thyme-moss, Horn Calcareous Moss, Swan-neck Moss

A common woodland moss forming neat tufts of upright stems 2–5 cm tall, with broad, toothed leaves that show clear seasonal variation — bright green new growth at the tips contrasting with dark green older leaves below. One of the most abundant mosses in British woodlands, it does best on acidic substrates like humus, rotting logs, and stream banks. Its compact habit and tolerance of deep shade make it well suited to closed terrariums. In spring it produces its characteristic curved sporophytes, which arch like a swan's neck before the spore capsule matures.