Hypoxylon fragiforme is a multiperitheciate carbonaceous pyrenomycete known from Europe and North America.

The semispherical lumps are up to 15 millimetres (5⁄8 in) wide and covered with 15–25 bumps in maturity.

[1] Specimens are reddish when young, and they produce orange pigments when mixed with KOH.

Similar species include Hypoxylon howeianum, which can be differentiated microscopically by smaller ascospores.

The anamorph of H. fragiforme sits on a fuzzy green subiculum while the anamorph of H. howeianum sits on radiating hyphal cords, reminiscent of a white spiderweb-like structure.