Species: Opegrapha calcareaGrowth type crustose, graphid.
Opegrapha calcarea includes O.conferta, O.chevallieri, O.saxatalis and other former species.
Variable. Thin or immersed thallus with black, unbranched lirellae to 1.2mm. Lirellae can be star-shaped, slit-like or form piled heaps. Asci are 8-spored, spores 3-septate, 16-20 x 4-5(-6.5) Ám. Microscope photograph below.
Occurs on shaded calcareous or basic rocks and on man-made substrates. Also found on shaded basic to acidic coastal rocks.
Thallus: chemical reactions negative.
Similar: Opegrapha cesareensis. Lirellae to 2mm, spores 4-5 septate, 15-22 x 4-5 Ám.