Irish lichens

Opegrapha atra
Order: Arthoniales       Family: Arthoniaceae

Species: Arthonia atra (Opegrapha atra)

Growth type crustose, graphid.
Photos: On Ash trunk. Ballingeary, Cork, SW Ireland.

Thin or +/- evanescent whitish or green-grey thallus, the short (1mm), prominent lirellae with central slit often densely crowded at centre of thallus. Pycnidia rare. Forms extensive mosaics on young trees. Asci 8-spored, spores 3-septate, 13-18(-20) x 2.5-4(-5) Ám. Microscope photograph below.
Thallus negative. Exciple K+ olive-green, hymenium I+ blue, epithecium brown or green-brown, K+ olive-green.

Common on the trunks, branches and twigs of trees with smooth shaded bark, rarely found on fences.

Opegrapha atra

Opegrapha atra

Microscope photograph
Opegrapha atra
Opegrapha atra. December 2008 and April 2012

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