Description: Fruiting bodies are usually large, vary in shape, from narrow and upright, globose, through to flattened against the substrate. They are mostly black, although a few have rich orange or purple colours. A few genera of Xylariaceae are have microscopic fruiting bodies immersed in the substrate, these are not treated here.
All fungi in this family have dark ascospores, mostly with a germ slit, some with a germ pore. Saprobic on wood or tree fern fronds.
Fruiting bodies usually contain numerous perithecia arranged in a single layer just below the surface. In Rosellinia, Helicogermslitta and Astrocystis, the perithecia are single, although often grouped in large masses.