Astrothelium sipmanii is a species of corticolous (bark-dwelling) lichen in the family Trypetheliaceae.

The type was collected by Harrie Sipman in the Upper Takutu District; here, in savannah forest, it was found growing on the smooth bark of trees.

The ascomatal walls are carbonized (blackened) and up to about 80 μm thick; the ostioles (pores) are apically situated, black, and concave.

Astrothelium sipmanii makes ellipsoid-shaped ascospores with 5 septa, and measure 100–150 by 35–40 μm.

[1] Astrothelium curvisporum and A. pustulatum share some similar characteristics, but can be distinguished by differences in spore shape and septation.