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(Map updated: 11 August 2009)

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 characteristics

• 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