This genus was based upon C. guyanense Hook. f. in Hook. Ic. 12. pl. 1148. 1873, collected by Schomburgk in "British Guiana." The flowers were described as being "solitarii, breviter pedicellati," with the lobes "late oblongi" and "obtusi," the capsule as "septicide 2-valvis." In Carolus Schumann's treatment in Martius's Flora Brasiliensis 6(6) : 246. 1889, the capsule is described as glabrous ("ut videtur glabra"). In the plate referred to, the leaves are shown as of an obovate type, the flowers are solitary on short pedicels, and the corollalobes are rounded at the summit and only half the length of the corolla-tube.
In the collections of this species made subsequently in British Guiana and adjacent Venezuela, it is evident that there is considerable variation in foliage and flower, even on the same plant. Leaf-blades are found to vary from oval-oblong to suborbicular and nearly as broad as long to oblong-obovate or obovate and up to 2 1/2 times as long as broad, the flowers m a y be solitary on short pedicels or two or three together borne on an elongated peduncle up to 5 cm long, and the corollas m a y be variable on the same plant, differing not only in relative length of tube but in the type of apex from rounded or obtuse to distinctly acuminate. Moreover, the capsules are appressed-pubescent with varying degrees of pubescence. Such variation is well brought out in the collections by Maguire & Fanshawe 23169 from British Guiana and Steyermark & Nilsson 348 from Venezuela, showing complete ranges of variation. In the latter collection some of the calyx-lobes are greatly elongated to 17 mm long and some of the capsules are as much as 18 mm long.