Fruiting body a stalked or sessile sporangium or a plasmodiocarp. Peridium thin, membranous, covered with a more or less dense coating of calcareous crystals either scattered loosely over the surface or combined into a crust. Columella usually present, but sometimes reduced to a thickened, calcareous base. Capillitium of branching and anastomosing limeless threads often bearing dark, nodular thickenings. Spores black in mass.
This is a very large and diverse genus, and more than 70 species have been described (Lado 2001). Nine of these are known from New Zealand.