All photographs copyright (2003-2013) by Kris H. Light

The <em>Usnea</em> species of lichens have a central core made up of hyphae strands called the <em>axis</em>; it gives the branches rigidity. This core can be revealed by gently pulling the green cortex and medulla layers off. The axis is an identifyin...
The Usnea species of lichens have a central core made up of hyphae strands called the axis; it gives the branches rigidity. This core can be revealed by gently pulling the green cortex and medulla layers off. The axis is an identifying characteristic for this genus.

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