Usnea, commonly known as “Old Man’s Beard” or “Tree Hair,” is a unique type of lichen, not a moss or a traditional plant. It results from a symbiotic relationship between a fungus and an alga, forming a distinct organism that appears as stringy, greenish-gray strands. These fruticose lichens grow in a shrubby or tassel-like manner, anchored to bark or twigs.
Identifying Usnea
Usnea exhibits a branching, thread-like, or bushy appearance, varying in color from pale green to yellow-green, or grayish-green, sometimes with reddish or variegated hues. Its branches are round, not flattened. The most definitive identification method is the “pull test” or “elastic core test.” Gently pulling a strand reveals a white, elastic inner cord, unique to this genus. If this core is absent, it is not Usnea.
Preferred Habitats and Locations
Usnea thrives in environments with high humidity, cool temperatures, and clean air. Its presence often indicates low air pollution due to its sensitivity to sulfur dioxide.
It is widely distributed across temperate and tropical regions, growing primarily on trees, though occasionally found on rocks. In forests, it commonly grows on conifers (pine, fir, spruce) and deciduous trees (oak, maple, birch, apple). It can be found on healthy, dead, or dying branches, often high in the tree canopy. Areas with consistent moisture, like the Pacific Northwest, are particularly conducive to its growth, where strands can reach several meters.
Distinguishing from Look-Alikes
Several lichens and even some plants can be mistaken for Usnea due to similar appearances, requiring careful identification. Ramalina species, for instance, can form long, thin hairs resembling Usnea but typically have flatter, less extensively branched thalli and lack the elastic central cord. Similarly, Alectoria, sometimes known as “Witch’s Hair,” shares visual similarities but its branches snap cleanly, unlike Usnea. Spanish moss (Tillandsia usneoides) also bears a resemblance, even deriving its Latin name from Usnea, but it is a flowering plant and possesses a black inner cord instead of Usnea’s white elastic core.
Ethical Foraging Practices
Responsible collection of Usnea is important due to its slow growth and environmental sensitivity. Collect Usnea only from fallen branches or trees, especially after windy weather, to minimize impact on living organisms. When harvesting from living trees, take only small amounts (no more than a quarter to a third) to allow for regeneration. This ensures plenty remains for wildlife (which uses Usnea for forage and nesting) and supports the lichen’s reproduction. Always check local regulations and land ownership before foraging to ensure compliance and promote sustainable practices.