Verrucariaceae Thelidium papulare Growth type crustose. Chemical results negative. Infrequent on damp, basic rocks; limestone, calcareous sandstone, basalt and mudstone Immersed brown or greyish thallus, the large black perithecia (to 0.8mm) slightly depressed at the apex, often with thalline collar at base. Spores are 3(-5) septate, (27)36-50(65) x (11)14-19(23) µm. Micrograph below. Similar: Thelidium decipiens, spores 1-septate. Thelidium incavatum, spores 3(-5) septate, perithecia +/- immersed.

Microscope photograph

Thelidium papulare
All Saints, Branksome Park, Dorset. February 2017