Volume 8, part 1 covers two families. Convolvulaceae consists of about 50 genera and 1500 species, nearly all cosmopolitan in distribution, but best developed in tropical and subtropical regions. Cuscutaceae is a monogeneric family sometimes included in the Convolvulaceae but distinct from this because of the different habit and them being parasitic, usually without chlorophyll, without glandular hairs and the vascular system being reduced.