Acanthothecis kalbii is a species of script lichen in the family Graphidaceae.

It was described as a new species in 2009 by Manuela Dal-Forno and Sionara Eliasaro.

The specific epithet honours German lichenologist Klaus Kalb.

[1] The lichen has a smooth, off-white thallus that grows on bark.

Its ascospores, which number eight per ascus, are ellipsoid with 3 to 5 transverse septa; they measure 9–15 μm long by 4–5 μm wide.