oursop (Annona muricata) is a tropical fruit that is native to the Caribbean and the Americas. It is also known as graviola, guanabana, sauersak, and guayabano. The fruit is large, oval-shaped, and can weigh up to 10 pounds. It has a green exterior with spines, and white, fibrous flesh. The fruit has a sweet taste, and can be eaten fresh, or made into juice or smoothies.