Caloplaca arenaria (Pers.) Müll. Arg.
Caloplaca lamprocheila (DC.) Flagey
Granite firedot, sandwort orange lichen
Granite firedot lichen occurs worldwide.
Identification: This rock-dwelling lichen is so thin that it looks at first like rust on the rock. 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.
Caloplaca arenaria on Stephen Sharnoff Photography
Caloplaca arenaria on the Mushroom Observer
Caloplaca arenaria on the Stridvall Family Domain
Caloplaca arenaria on CalPhotos
Caloplaca arenaria at Wisconsin Mushrooms
Caloplaca arenaria description by Thomas H. Kent, last updated 25 May 2020.