Ikaeria serusiauxii, a new Caloplaca-like lichen from Macaronesia and mainland Portugal, with a lichen checklist for Porto Santo.

The new species Ikaeria serusiauxii (Teloschistaceae, lichenized Ascomycetes) is described from the Madeira Archipelago, Canary Islands and continental Portugal. It is a crustose lichen on twigs and branches of trees and shrubs in xerophytic maritime vegetation. Superficially it is similar to Caloplaca cerina and C. haematites, from which it differs by the often black apothecium margin, very thick spore septa, black pycnidium ostioles, and the presence of the pigment Cinereorufa-green instead of Sedifolia-grey. ITS sequences suggest Ikaeria aurantiellina (syn. Caloplaca aegatica) as the closest relative. Added is a preliminary lichen checklist for Porto Santo (Madeira Archipelago, Macaronesia). [ABSTRACT FROM AUTHOR]