Studies in the North American Convolvulaceae, II. The Genus Operculina

Abstract

The original description of the genus Operczulili S. Manso was based upon the operculum-like structure, quatrefoil in shape, which tops the capsule in the type species 0. Inacroca;'pa Urban. An examination of a large number of specimens of this and related species shows that the presenlce of an operculumn is not in this case a generic distinction, for often of two species closely and evidently related by all other characters, one will have a well developed operculum and the other noine or sometimes in a few specimens, only vestiges of one. While the type has irregular dehiscence some other species with an operculum have a valvular dehiscence to the capsules. The commnon features, however, that do occur throughout a considerable group of species that seem by a preponderance of characters to center congenerically about the type of Operc/lila are as follows: the pear-shaped calyx, rounded at the base and narrowed above; the large imbr-icated sepals more or less chartaceous or parchment-like in fruit; the broadly campanulate-funnelform tube of the corolla, and the strongly contor-ted anthers which are often protruding from the tube of the corolla. The capsules are usually large and thin-walled, often the upper hemisphere of the capsule thicker than the lower. This extension of the genus seems to be the only satisfactory way to place properly those species variouLsly assigned to ferremia, Batlals, and Ipolloeda, with spirally-twisted arithers and other characters in common with species now placed in Opercuzliiia.