Adaptations of Polytrichum Moss

Fire Adaptation

• The juniper haircap moss (P. juniperinum) and others are capable of surviving some surface fires because they have rhizomes that penetrate deeply enough into soil that they do not burn. This moss occurs in ecosystems with frequent fires as well as in ecosystems where fire is less common. Polytrichum mosses also spread using wind-dispersed spores. This allows the moss to quickly colonize burned sites.

Tissue Adaptations

• Most mosses have leaves consisting of a single layer of cells, making them better able to take up water but also more vulnerable to water loss. Polytrichum leaves are several cell layers thick and contain differentiated photosynthetic tissue. Thick-walled terminal cells protect underlying tissue and traps humid air in air pockets between cells, allowing enough gas exchange for photosynthesis while minimizing water loss. Some Polytrichum species also have a lamina that folds over the photosynthetic tissue, behaving similarly to the protective epidermis that the leaves of higher plants.

Moisture-Retaining Adaptations

• Polytrichum moss leaves have a unique adaptation that allows them to better withstand dry conditions. Under moist conditions, leaves spread away from the stem and permit a maximum use of light when moisture is adequate. However, under dry conditions, the leaves curve and twist around the stem. This behavior minimizes water loss and protects chlorophyll.

Regeneration

• Polytrichum moss’ reproductive methods allow it to persist and better populate new areas. It regenerates sexually from spores, which are released from the sporophytes when weather is dry. The lightweight spores are carried by the wind for long distances and require a moist substrate to germinate. Polytrichum species also reproduce asexually from specialized tissues and broken plant parts. Rhizoids and stem fragments produce new stems capable of regenerating, even following a period of drought-induced dormancy.