The tubercle shape of a particular Coryphan-tha species has unique features and is, in fact, one of the best diagnostic features for differentiation between species. In general, tubercles are based on the shape of a cone with the upper part obliquely cut, rounded and more or less edged. The lower part is more or less bulging and sometimes keeled. The base is more or less enlarged. Another typical characteristic feature is the shape of the contour line where the enlarged base of the tubercle joins the plant body. Young tubercles usually are rounder, but develop a more characteristic shape with age. The shapes and measurements given by us always concern tubercles of average age.
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