About Usnea trichodea Ach.
Description: Usnea trichodea hangs from tree branches and twigs, and can grow up to 30 cm (12 inches) long. Its main branches are smooth, slender, and measure less than 0.4 mm (0.02 inches) in diameter. Side-branches grow from the main branches at obtuse angles at regular intervals. The lichen's thallus is split into articulating sections, with raised cracks forming between these sections. The medulla is dense and white, while the central axis is reddish-brown. This species can be mistaken for Usnea longissima, but its unique branching structure and reddish axis make it distinguishable.
Distribution and habitat: Usnea trichodea is found in eastern North America, where it grows on trees. In Canada, its range covers Ontario, New Brunswick, Newfoundland, Nova Scotia, Prince Edward Island, and eastern Quebec. In the United States, its range extends south to Texas and Florida.
Ecology: Like many sensitive lichens, Usnea trichodea and Evernia species will become unhealthy and die when exposed to sulphur dioxide. This means these lichens can be used as indicators of air pollution. In a study of Nova Scotia, researchers found that tricolored bats (Perimyotis subflavus), which normally roost in tree foliage across most of their range, roosted exclusively in the dangling thalli of Usnea trichodea. The lichen in this area typically grew on conifers, most of which were spruce species. Study authors speculated that tricolored bats may use this lichen—which contains usnic acid—to reduce parasitism, because the roosting bats were found to have no ectoparasites.
