Irish lichens

Rhizocarpon petraeum
Order: Lecanorales       Family: Rhizocarpaceae

Species: Rhizocarpon petraeum

Growth type crustose.
Photos: On coastal rock. Ballyrisode beach, Cork, SW Ireland.

Chalky-white cracked and areolate thallus with a dark prothallus. Irregularly-shaped black apothecia (to 1mm) with paler margins, often arranged in concentric rings. Green-brown epithecium. Spores muriform, initially colourless but dark when old, 20-50 x 13-25 Ám.

Occurs on intermediate rocks (slightly-basic to slightly-acidic) in both urban and rural areas. Medulla: K+ yellow, P+ yellow-orange

Similar: Rhizocarpon umbilicatum. Randomly scattered apothecia with smaller sub-muriform spores. Restricted to pure limestones.

Rhizocarpon petraeum       Rhizocarpon petraeum

Rhizocarpon petraeum
Rhizocarpon petraeum. Ballyrisode beach, Co. Cork. February 2009

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