Opegrapha atra Arthoniaceae
Arthonia atra (Opegrapha atra)

Growth type crustose
Chemical results: Thallus negative. Exciple K+ olive-green.
Hymenium I+ blue, epithecium brown or green-brown, K+ olive-green.

Common on smooth, shaded trunks, branches and twigs, rare on wood. Forms extensive mosaics on young trees but avoids nutrient-enriched bark. Host to Milospium graphideorum and Muellerella polyspora

Short (1mm) prominent lirellae with central slit, often densely crowded at centre of thin or +/- evanescent thallus. Pycnidia rare. Spores 3-septate, 13-18(-20) x 2.5-4(-5) Ám. Microscope photograph below.

Opegrapha atra

Opegrapha atra

Microscope photograph
Opegrapha atra
Opegrapha atra
On Sycamore. Kimmeridge, Dorset. January 2013

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