The Polytrichum genera buck the trend of mosses a bit by being a little more than just a lush looking carpet on the woodland floor! Whilst the species vary they do tend to be more distinctive than some of their cousins and give the casual observer a chance of identifying it. This one, Polythrichum commune, is also known as the common haircap and forms large communities (or communes) of tiny, dense, fir-tree like plants and it the density of those individual plants that make it distinctive.
It is a common species too and can be found where the conditions are wet and so look for it by streams in woodlands, or on wet heaths and bogs. Its presence indicates an acid soil.
Care needs to be taken to avoid confusing this with Polytrichum formosum which has similar stems but they are smaller and less densely packed.