Crusty Yellow Lichen

Description:

Crusty” lichens simply form crusts over their substrates, without distinctive lower surfaces. Some are composed entirely of grains of varying sizes. They can be smooth and continuous over a surface, or broken up by cracks, or divided into “areoles” -- separate small spots.. Lichen colors vary widely due to presence or absence of special pigments, though in the absence of these, lichens are generally gray or greenish gray. When a lichen is wet, the cortex becomes more transparent and the underlying photobiont layer becomes visible, making a gray or brown lichen turn bright green or olive in color. But a variety of bright pigments may be deposited in the cortex: most widespread is pale yellow usnic acid, but other pigments generate a variety of yellow, orange, or red lichens. Colors vary within species due to light exposure, genetics, age, etc. Light seems to be a primary factor, since the deepest pigments -- yellow, orange, red, even brown -- occur in the most exposed, often dry habitats. These pigments appear to protect the underlying photobionts from excessive ultraviolet radiation

Notes:

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