How to Grow and Care for Shield lichens

Hammered shield lichen is noted for its pollution tolerance. It is a widespread grey flat lichen that is mostly found upon tree bark and occasionally rocks. Hammered shield lichen is named for the depressions within the lobe which give it a hammered appearance.

It was first described in 1753 by Carl Linnaeus with the name Lichen saxatilis. Erik Acharius transferred it to Parmelia in 1803. The lichen has a greenish-gray to bluish-gray thallus that can turn brown in exposed locations. It typically grows on rock, although it is sometimes found on bark or wood. Parmelia saxatilis is used to make dyes with deep red-brown and rusty-orange colors. Known as "crotal" in Scotland, it was used to dye traditional cloths including Harris tweed. A somewhat similar species with a cosmopolitan distribution is Parmelia sulcata, which generally grows on trees.