The question of whether reindeer moss is alive is common, as its appearance often suggests it is nothing more than a brittle, dried-out fragment. The definitive answer is yes, this organism is fully alive, but its classification and survival strategy are complex. The confusion stems from its remarkable ability to enter a state of deep dormancy, making it look and feel lifeless, which is key to its unique biology in harsh northern climates.
What Exactly Is Reindeer Moss?
Despite its misleading common name, reindeer moss (Cladonia rangiferina) is not a true moss, which belongs to the group of non-vascular plants called bryophytes. It is actually a lichen, a complex organism resulting from a mutualistic partnership between two entirely different life forms.
The structure of the lichen is built upon a symbiotic relationship involving a fungus (mycobiont) and a photosynthetic partner (photobiont), either an algae or cyanobacteria. The mycobiont forms the majority of the physical structure, offering protection and anchoring the organism. The photobiont lives within the fungal filaments and produces food through photosynthesis. This dual nature makes the lichen fundamentally different from a plant. The lichen’s structure, often described as shrub-like or fruticose, is densely branched, contributing to its sponge-like ability to absorb moisture from the atmosphere.
The Secret to Survival
The ability of reindeer moss to appear dead and then revive is rooted in two interconnected biological strategies: poikilohydry and desiccation tolerance. Unlike vascular plants, which regulate and store water, reindeer moss is poikilohydric. This means its internal water content equilibrates with the moisture level of the surrounding air, causing the lichen to dry out completely when the air is dry.
This rapid water loss causes the lichen to become brittle, and its color changes from soft green or pale gray-green to an almost white or silvery hue. In this desiccated state, the organism enters dormancy (anabiosis), where virtually all metabolic activity, including photosynthesis and respiration, stops. This shutdown allows its cells to survive prolonged periods in extreme cold or drought conditions without being destroyed.
Desiccation tolerance is the ability to fully restore normal metabolic functions upon rehydration. When moisture returns through rain, dew, or fog, the lichen rapidly absorbs water, regains its spongy texture, and its metabolic processes resume within minutes or hours. This capacity means that even when it has lost over 90% of its water content, the cellular structures remain intact and ready to spring back to life.
Reindeer Moss in the Ecosystem
The organism’s common name is derived from its ecological role as a primary food source for grazing animals in northern latitudes. Caribou and reindeer rely heavily on this lichen, especially during harsh winter months when other vegetation is buried under snow. The lichen contains carbohydrates that provide the necessary energy to survive the season.
The growth rate of Cladonia rangiferina is slow, often measuring only a few millimeters per year. This slow growth, combined with its fragility when dry, makes it sensitive to disturbances like overgrazing or trampling. Because it absorbs its water and nutrients directly from the atmosphere, it also readily absorbs airborne pollutants, making it a valuable bioindicator of air quality.
Its extensive mats stabilize the soil in nutrient-poor environments across the Arctic tundra and boreal forests. By fixing nitrogen from the atmosphere, the lichen helps enrich the substrate, paving the way for other, more complex plant life to colonize the area.