Description: Found occasionally on limestone fragments and pebbles sheltered from direct rain and disturbance, P. byssophila is very like P. linearis. What distinguishes this species is the combination of grey-green-brown thallus, specialised habitat and the three- (to seven)-septate spores. Often the spores show little variation from the three-septate kind, but it is worth persisting, especially when a collection has a clear, visible thallus. In P. linearis the thallus is always immersed; P. chlorotica favours siliceous rock. In Ireland, the species is known from the Burren, County Clare and from County Westmeath.

Key Identification Features:

• Thallus exposed, grey-green to brown; perithecia buried in the thallus, the involucrellum (protective and thick outer layer of cells) with some purple pigments
• Spores three- (to seven)-septate, 18.5–24 x 4–5.5µm, on shaded limestone or basic siliceous pebbles.

Original text submitted by Vince J. Giavarini

Distribution Map from NBN: Porina byssophila at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Porina byssophila at iNaturalist World Species Observations database.