Homostegia piggotii (Berk. & Broome) P. Karst.
Dothidea piggotii Berk. & Broome
Visible on host thallus as black round spots, immersed at first, flat, then slightly prominent and finally as convex or even globular piles, black, surface irregular and humpy. Perithecia immersed, into black globular piles. Ascospores broadly ellipsoid, slightly curved, 3-septate, constricted at septa level, 20-23 x 7-9 µm. Grows on impaired or scraggy foliose thalli of Parmelia, notably Parmelia saxatilis.*