Homostegia piggotii (images of British lichenicolous fungi)

Ascomycota, Dothideales: forms irregular to rounded, black, stromatic areas on the host thallus, in which are embedded the perithecia; spores 3-septate, (18-)20-23(-26) × 7-8.5(-10) 痠 ) (figures from Hawksworth, 1983). On somewhat moribund thalli of Parmelia species, locally common at least in the west. The rounded stromata are often slightly raised from the thallus surface and can be mistaken for the apothecia of Abrothallus parmeliarum, which is frequent on the same hosts.

Refs: Hawksworth (1983), 7.

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Alan Silverside's Lichen Pages: Lichenicolous Fungi