... Trabutia quercina (Fr. & K. Rud.) Sacc. & Roum. ... is an ascomycetous fungus which forms perithecia (fruiting bodies of the fungus) within the black stroma (protective covering). Typically, many perithecia are embedded in a single stroma. Asci contain 8 subhyaline, navicular ascospores. [In addition to its appearance on Quercus virginiana] Trabutia quercina has also been reported on other species of Quercus

SYMPTOMS AND SIGNS. The black spots are round to irregular in shape and up to 7 mm. across. Stromatic development is usually on the upper or lower surfaces of leaves, but occasionally, on both sides. Stromata are surrounded by brown, necrotic leaf tissue which tracks along the main veins of infected leaves. Spots sometimes coalesce to form larger spots. ... The fungus matures in old overwintering leaves.

- N. E. El-Gholl and T. S. Schubert: (1987) Tar spot of live oak^©