ostridia possess no one typical colony morphology. They are generally a large colony (>2mm) with irregular edges or swarming growth. Some Clostridia form small, convex, non-hemolytic colonies with a smooth edge. Other Clostridia produce several different-looking colony types, so the culture appears mixed. A few Clostridium spp. have distinctive colony characteristics. Clostridium perfringens usually produces a double zone of beta-hemolysis. The inner zone shows complete hemolysis, whereas the outer zone may display partial hemolysis. Clostridium difficile produces a yellow ground-glass colony on CCFA. On blood agar, Clostridium difficile are usually 2mm or more in diameter after 24 hours of incubation, fluoresce yellow-green, and emit a horse stable odor. (Fluorescence should not be observed on CCFA because it itself is fluorescent).