Caloplaca arenaria (Pers.) Müll. Arg.

Granite firedot, sandwort orange lichen

Granite firedot lichen occurs worldwide.

Identification: This crustose rock-dwelling lichen is so thin that it looks at first like rust on the rock. It is usually glossy, and pale yellow, gold, or orange. It appears most commonly on granite, but can appear on other non-calcareous rocks. Its fruiting structures (apothecia) are dark red and very small, less than a millimeter across, wide and flat, like irregular tiles, without the white powdery covering that occurs in some other lichens. This is the only rock-dwelling lichen with such a dark red appearance.

Habitats: Non-calcerous rocks, especially granite, and sometimes on sand, which it helps to stabilize; in temperate and tropical areas.

Online References:

Caloplaca arenaria description by Thomas H. Kent, not updated.

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