The Polytrichales is a characteristic order of acrocarpous mosses with robust, narrow leaves and a transparent sheathing base and with longitudinal lamellae on upper (adaxial) surface – check with hand lens or under the dissecting microscope.
With a little practice you can cut a transverse leaf section with a razor blade to reveal the structure of the lamellae – the shape of the terminal cell of which can be key to the identification of different species.
The capsule is held erect to horizontal and the calyptra (the protective cap that covers the immature capsule) is cap-shaped and usually hairy (hence “poly-trichum” – meaning “many hairs“).
Polytrichales are found growing on the ground in moorland and woodland, often very abundant.
There are about 200 species world wide.
Click on the images below to see more detail of two common mosses in the Polytrichales:
Atrichum undulatum – the undulate leaves and parallel lines indicating the presence of lamellae on the midrib are the best ID features, common on soil in woodland
Polytrichastrum formosum – forms carpets looking like little pine trees, common on soil (usually at least mildly acid) in woodland
The featured image at the top of this post shows a transverse section through a leaf of Polytrichastrum formosum showing the broad midrib with vertical lamellae.