Beard lichen

Description:

Like other lichens it is a symbiosis of a fungus and an alga. The fungus belongs to the division Ascomycota, while the alga is a member of the division Chlorophyta. Members of the genus are similar to those of the genus Alectoria.:148 A distinguishing test is that the branches of Usnea are somewhat elastic, but the branches of Alectoeria snap cleanly off.

Habitat:

Like other lichens, Usnea often grows on sick or dying trees due to the pre-existing loss of canopy leaves, allowing for greater photosynthesis by the lichen's algae; this leads some gardeners to mistakenly blame the lichen for the tree's leaf loss and illness. Usnea is very sensitive to air pollution, especially sulfur dioxide. Under bad conditions they may grow no larger than a few millimetres, if they survive at all. Where the air is unpolluted, they can grow to 10–20 cm long. It can sometimes be used as a bioindicator, because it tends to only grow in those regions where the air is clean, and of high quality.