Order: Arthoniales Family: Roccellaceae
Species: Opegrapha viridis
Photos: On Ash. Caha Pass, Co. Cork, SW Ireland.
Identification confirmed by J Douglass
Forms small patches of thin or inconspicuous, brownish or olive-green thallus. The small, scattered apothecia are short and +/- rounded and 'button-like' with a narrow, slit-like disc. Asci 8-spored, spores (8-)11-15 septate (with a perispore), 23-60 x 6-9 Ám. Chemical reactions negative. Microscope photographs below.
Found in SW Ireland, usually on the shaded bark of young Hazel, Holly, Oak and salix in old woodlands.