The Apocynaceae or dogbane family is commonly so-called because of its toxic nature. The name Apocynum originally applied to a plant that was supposedly poisonous to dogs. The family at present includes about 425 genera. The number of species varies greatly from 1500 to 6000 depending on the source. They are spread widely across tropical and subtropical areas, and a few genera even extend into temperate zones. Some of the more familiar members are oleander (Nerium), frangipani (Plumeria), periwinkle (Vinca), Natal plum (Carissa), and now that this family has been placed in with the Apocynaceae, the milkweeds (Asclepias). Milky sap is a general characteristic of most members of the family. The leaves are usually simple and opposite sometimes whorled, and the flowers typically contain five at least partially fused petals. The fruits are follicles, capsules, or berries.