The black fruitbody is typically long and club shaped with a rounded or tapering tip and brownish scales.  It is initially covered in greyish asexual conidia, with the sexual stage developing later.  Inside is a white stroma with the spore-producing perithecia at the surface, seen as tiny pimples on the outside of the club.  When the spores are mature, they are ejected through a minute hole or ostiole. 

Dead Man's Fingers (Xylaria polymorpha) is usually larger and more rounded or squat, and occurs on a variety of deciduous trees, but both species are variable in form.  Sometimes confused with Earth-tongues (Geoglossum) but these grow in grasslands, not on dead wood.

Photograph in habitat, note substrate and associated tree species

On dead wood, almost always Sycamore.