They are sometimes seen with cirrus, cirrocumulus, altocumulus, and stratocumulus. It is a cloud species attached to the cloud genera cirrus, cirrocumulus, altocumulus and stratocumulus. Cumulus mediocris may form as a result of a partial transformation of altocumulus or stratocumulus. All three are associated with the stratiformis species of altocumulus and stratocumulus. Stratocumulus clouds are same in appearance to altocumulus and are often mistaken for such. The cumulus turn into stratocumulus or altocumulus depending on their height. Species of the clouds include cirrus castellanus, cirrocumulus castellanus, altocumulus castellanus and stratocumulus castellanus. Like other cumuliform and stratocumuliform clouds, altocumulus signifies convection. This fairly common phenomenon is most often observed in altocumulus, cirrocumulus, lenticular, and cirrus clouds. Stratocumulus is also often, though not always, darker in colour than altocumulus. An altocumulus castellanus, however, can be identified by the lack of a well-defined base. The stratocumuliform group is divided into cirrocumulus (high-level), altocumulus (mid-level), and stratocumulus (low-level).