Order: Arthoniales Family: Roccellaceae
Species: Opegrapha niveoatra
Photos: On Laburnum. Kinsale, Co. Cork, SW Ireland.
Identification confirmed by John Douglass
Thin dull-grey to olive-brown thallus, similar to O. vulgata but with shorter lirellae, to 1mm long. Scattered or contiguous apothecia, discs becoming partly exposed, exciple +/- uneven. Spores 4-7 septate, conidia worm-like. Often sterile but pycnidia abundant. Chemical reactions negative.
Found on neutral and basic-barked trees; Ash, Sycamore and Elm. Most frequently recorded from eastern Ireland.
Similar: Opegrapha vulgata. Larger discs, conidia sickle-shaped
Opegrapha niveoatra May 2010