Old Man's Beard

Old Man's Beard hangs from tree branches in long, pale green streamers up to several meters long. It's a fruticose (shrubby) lichen that doesn't parasitize its host tree - it simply uses branches as scaffolding to access light and atmospheric moisture. This lichen is exquisitely sensitive to air pollution, disappearing from areas with poor air quality.

This makes Usnea a biological air quality monitor. Its presence indicates clean air; its absence signals pollution. The business parallel is reputation indicators - entities whose presence or absence signals environmental quality. When top talent leaves a company or industry, it's often an early warning sign, like Usnea disappearing from polluted forests.