Giant moss, seen along the lower leg of the Twin Falls Circuit track
in Springbrook National Park.
Related to common haircap moss.
Most mosses are regarded as poikilohydric i.e. strongly dependent on humidity and free surface moisture to function, shrivelling when dry, as they lack a cuticle and effective water-conducting conduits. However because the Polytrichaceae possess comparatively well-developed water conducting central strands in their stems, they are somewhat endohydric, and so can continue to function and grow when not wet.
The water-conductive strands in the centres of the stems are composed of hydroids, elongated cells with thickened walls and obliterated plasmodesmata that undergo programmed cell death upon maturation, as the tracheids of vascular plants do. But they don't have pores in the end walls like the tracheids of higher plants, and they don't have any lignin in their cell walls either.
Despite the absence of inter-connecting pores between hydroids, the specific conductivity of the stems of some Polytrichaceae are higher than some conifers (e.g. Sequoia sempervirens) and comparable to some angiosperms, at least under humid conditions.