The passage of time marked in textures ...
From outer, new edge inward; leafy, greenish thalli shrink, turn grey, then whitish and crumbly as they mature. |
In crustose lichens, the area along the margin is where the most active growth is taking place. ... Most crustose lichens grow only 1–2 mm in diameter per year. (Wikipedia)
Some are huge, so they must be very old. - Margy
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