Abrothallus welwitschii is a species of lichenicolous fungus in the family Abrothallaceae.

[2] It grows on species of the foliose lichen genus Sticta.

[3] The type specimen was originally collected in Portugal in 1840 by Austrian botanist Friedrich Welwitsch, and it is after him for whom the species is named.

[5] The fungus has been collected throughout Europe, Africa (Kenya), New Zealand, South America (Chile), and northern North America.

Recorded hosts have been Sticta fuliginosa, S. limbata, S. nylanderiana, and S. sylvatica.