[From the Bulletin op the Tukkbv UorANicAL Club 35: 97-107,//. i-z. 1908] 



Studies in the North American Convolvulaceae — IV. The 



genus Exogonium 



HOMKR DOLIVER HoUSE 

 (WITH PLATES I AND 2) 



The genus Exogonium is based upon Ipomoca bractcata Cav., 

 a Mexican species, and with several other West Indian species 

 forms one of the natural groups of species usually referred to 

 Ipomoca. The group is recognized as a genus by Peter and by 

 Hallier, and as a section of Ipomoca by Grisebach and by Meissner. 

 Ipomoca Piirga, which has sometimes been referred to Exogonium, 

 appears to be more closely related to a group in Ipomoca, of which 

 not all the members possess the salverform corolla and exserted 

 stamens of /. Purga, and should more properly be retained in 

 Ipomoca. Until very recently the genus was regarded as almost 

 wholly confined to the West Indies. Recent collections in 

 southern Mexico have shown that four species occur in Mexico, 

 one of them apparently identical with E. argcntifolium, of the West 

 Indies. 



EXOGONIUM Choisy, Mem. Soc. Phys. Genev. 6 : 443. 

 1833. — In DC. Prodr. 9: 346. 1845 



Perennial, trailing or twining vines, usually with woody stems. 

 Leaf-blades entire or lobed. Flowers several on axillary peduncles 

 or solitary ; bracts large and colored, sometimes inconspicuous 

 or absent. Sepals membranaceous or subherbaceous, equal or 

 unequal, never awned. Corolla scarlet or white ; the tube often 

 slender and constricted at the throat or expanding above in a 

 salverform or funnelform limb. Stamens and style exserted or 

 protruding, rarely included. Ovary 2-celled, 4-ovuled. Capsules 

 ovoid, thick-walled, apiculate. Seeds with a long coma of hairs 



97 



