This is one of the first mosses that a beginner is likely to get familiar with. When it is growing in favourable conditions, such as in stubblefields, it can cover many square metres and the numerous capsules catch the eye.
The books tell you that it is an easy species to identify and, when its capsules have just matured, so it is. The lack of any peristome and a capsule that is about as wide as it is long and widest at the mouth are characteristic. However, young capsules are relatively elongate and in that condition people may misidentify it as T. modica, which is in many areas a much more uncommon plant.
One good difference to look for is the way the leaf of T. truncata has margins that are plane, or only slightly recurved, whereas T. modica has leaves that are distinctly recurved in mid-leaf.
Furthermore, the capsule lids of both Tortula species are beaked and this character can be handy to distinguish immature sporophytes from Microbryum davallianum and M. starckeanum, both of which have conical or mamillate capsule lids.Read the Field Guide account