Helvella lacunosa, also known as the slate grey saddle or fluted black elfin saddle, is an ascomycete fungus of the family Helvellaceae. It is probably the most common species in the genus Helvella. The mushroom is readily identified by its irregularly shaped grey cap, fluted stem, and fuzzy undersurfaces. It is found in Eastern North America and in Europe, near deciduous and coniferous trees in summer and autumn.