Mycoblastus sanguinarius (L.) Norman
Bloody Heart Lichen, Blood Lichen
Identification: Grayish white or grayish green, with tiny gray “warts.” Occurs on the wood or bark of deciduous trees. This is a crustose lichen (a thin layer that almost looks like paint), but thicker than most. The apothecia (fruiting bodies) are shiny black dots less than ⅛" (3.2 mm) across. There is a bright red zone underneath (the reason for the name “bloody heart lichen”), but you’ll need to slice into it to see it. (I don’t know what the red-brown region is on the photo at right—I don’t think it is part of the lichen.)
Mycoblastus sanguinarius on Stephen Sharnoff Photography
Mycoblastus sanguinarius on the Stridvall Family Domain
Mycoblastus sanguinarius at Alan Silverside's Lichen Pages on LastDragon.org
Mycoblastus sanguinarius on Wikimedia Commons
Mycoblastus sanguinarius description by Thomas H. Kent, last updated 12 Oct 2018.