<P> Usnea australis, a fruticose form, growing on a tree branch </P> <Li> <P> Hypogymnia cf . tubulosa with Bryoria sp. and Tuckermannopsis sp. in the Canadian Rockies </P> </Li> <P> Hypogymnia cf . tubulosa with Bryoria sp. and Tuckermannopsis sp. in the Canadian Rockies </P> <Li> <P> Letharia sp. with Bryoria sp . on pine branches near Blackpine Lake, Washington State </P> </Li>

What is the role of each member of the lichen