Studies in the North American Convolvulaceae, II, The genus 



Operculina 



Homer Doliver House 



The original description of the genus Operculina S. Manso 

 was based upon the operculum-like structure, quatrefoil in shape, 

 which tops the capsule in the type species — 0. macrocarpa 

 Urban. An examination of a large number of specimens of this 

 and related species shows that the presence of an operculum 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 none 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 common 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 Operculina 

 are as follows : the pear-shaped calyx, rounded at the base and 

 narrowed above ; the large imbricated sepals more or less charta- 

 ceous or parchment-like in fruit; the broadly campanulate-funnel- 

 form tube of the corolla, and the strongly contorted 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 satislactory 

 way to place properly those species variously assigned to Merre- 

 mia, Batatas, and Ipomoea, with spirally-twisted anthers and other 

 characters in common with species now placed in Operculina. 





OPERCULINA S. Manso, Enum. Subst. 



Bras. 1 6. 1836 



Twining plants with woody or herbaceous, perennial stems, 

 entire or divided leaves. Stems or peduncles often more or less 

 winged. Calyx large, pear-shaped, constricted above, the closely 

 imbricated sepals scarious or chartaceous and often colored, 



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