This is the scarcer of the two common species of Tortula that have no peristome. Although straightforward to tell T. caucasica and T. truncata apart by capsule shape when lids have fallen, it is inadvisable to use this character for plants with immature capsules as in both species they may appear longer than wide.
There is, however, another little-known character that works for maturing capsules too. Immediately below the capsule mouth of T. caucasica there is a distinct band of 3-5 rows of small, quite thick-walled cells. In T. truncata, this is reduced to 1-2 rows of thin-walled cells.
Tortula pallida, recently added to the English and Welsh lists (see Sam Bosanquet’s Field Bryology article below), is very similar to T. caucasica and is usually found very close to the sea. It differs primarily in leaf shape and the colour of the seta and leaves.Read the Field Guide account