Nerium oleander, commonly known as oleander or rosebay, is a shrub or small tree cultivated worldwide in temperate and subtropical areas as an ornamental and landscaping plant. It is the only species currently classified in the genus Nerium, belonging to subfamily Apocynoideae of the dogbane family Apocynaceae. It is so widely cultivated that no precise region of origin has been identified, though it is usually associated with the Mediterranean Basin.

Apocynoideae is a subfamily of the flowering plant family Apocynaceae, also called the 'dogbane' or milkweed family, containing about 860 species across 78 genera. Several are of pharmacological interest; Strophanthus has furnished highly effective arrow poisons, due to their cardiac glycoside content. Apocynoideae also includes many popular landscaping and ornamental species, one of the best-known, and most infamous, being the oleander ; the subfamily also contains remarkable pachycaul genera like Adenium and Pachypodium.