Hylocomium splendens (Glittering Wood Moss) is a common bright green moss that’s widespread throughout the highlands.  It has an intricate structure with flattened branches and a distinctive red stem that makes it easy to tell apart from the equally common Tamarisk Moss (Thuidium tamariscinum). 

The branches are listed as bipinnate, or in other words the leaf stems split into smaller branches and individual leaflets grow from these. (See Wikipedia)

Although this species is visible throughout the year new "steps" or fronds grow from buds behind each years’ previous growth.  Eventually these form complex, feathery mats or "staircases" that can be aged by counting the number of steps.

In general, there two annual growth periods – once during the late winter / early spring, then again in autumn.  During periods of sustained drought, the moss can become dormant and conserve moisture by turning brown.