Astrothelium isidiatum (type collection) A–D thallus morphology A, B isidia developing in groups on areoles which are partly shed exposing the medulla of the areoles C isidia-like outgrows developing on lateral parts of areoles D isidia-like outgrowths developing directly from the endosubstratal parts of the thallus E, F a vertical cross-section through thallus with crystals present in the medulla (E) (in LPCB) G, H vertical cross-section through cortical layer (in LPCB). Scale bars: 1000 μm (A, B); 500 μm (C, D); 50 μm (E, F); 10 μm (G, H).