Mosses in the genus
Polytrichum are endohydric, meaning water is conducted from the base of the plant. While mosses are considered
non-vascular plants, those of
Polytrichum show clear differentiation of water conducting tissue. One of these water conducting tissues is termed the
hydrome, which makes up the central cylinder of stem tissue. It consists of cells with a relatively wide diameter called
hydroids, which conduct water. This tissue is
analogous to
xylem in higher plants. The other tissue is called
leptome, which surrounds the hydrome, contains smaller cells and is analogous to
phloem. '' showing parallel photosynthetic lamellae at 400x magnification. The green cells contain
chloroplasts.|alt= Another characteristic feature of the genus is its parallel
photosynthetic lamellae on the upper surfaces of the leaves. The leaves of most mosses are simply a single plate of cells, but those of
Polytrichum have more highly differentiated photosynthetic tissue. This is an example of a xeromorphic adaption, an adaptation for dry conditions. Moist air is trapped in between the rows of lamellae, while the larger terminal cells act to contain moisture and protect the photosynthetic cells. This minimises water loss as relatively little tissue is directly exposed to the environment, but allows for enough gas exchange for photosynthesis to take place. The
microenvironment between the lamellae can host a number of microscopic organisms such as parasitic
fungi and
rotifers. Additionally, the leaves will curve and then twist around the stem when conditions become too dry, this being another xeromorphic adaptation. It is speculated that the teeth along the leaf's edge may aid in this process, or perhaps also that they help discourage small invertebrates from attacking the leaves.
Polytrichum species are
dioicous, having separate male and female plants. The reproductive branches arise from the apex of the main gametophyte axis. ==Classification==