Glycosides occur mainly in plants from which the names have been derived. Digitalis purpurea, Digitalis lanata, Strophanthus grtus, and Strophanthus kombe are the major sources of the cardiac glycosides. The term 'genin' at the end refers to only the aglycone portion (without the sugar). Thus the word digitoxin refers to a agent consisting of digitoxigenin (aglycone) and sugar moieties (three). The aglycone portion (figure below) of cardiac glycosides is more important than the glycone portion.