Opegrapha calcarea Arthoniaceae
Arthonia calcarea (Opegrapha calcarea)

Growth type crustose
Chemical results negative

Occurs on shaded calcareous or basic rocks inland and basic or acidic coastal rocks. Also found on man-made substrates.
Includes O.conferta, O.chevallieri, O.saxatalis and other former species.

Can be very variable with star-shaped, slit-like or heaped black lirellae on a thin or immersed thallus. Spores 3-septate, 16-20 x 4-5(-6.5) Ám. Microscope photograph below.

Similar: Opegrapha cesareensis. Western coasts. Spores 4-5 septate. Opegrapha mougeotii. Spores 5-7 septate.

Opegrapha calcarea

Opegrapha calcarea

Opegrapha calcarea

Microscope photograph
Opegrapha calcarea, spores
Opegrapha calcarea
Kimmeridge and Portland, Dorset. January and September 2013

All images used are copyright. Please contact me if you find errors.