Grapefruits (Citrus paradisi) are round fruits with a thick outer skin and fibrous inner flesh held together by a white pith. Depending on variety, little white seeds can be found toward the center of a grapefruit, and the color of the flesh can be red, pink, or white.
Health Benefits of Grapefruits:

Increased Immune Function
Reduced Cancer Risk
Protection Against Heart Disease
Grapefruit is ranked low on the glycemic index (GI) and therefore is advocated as a good diet fruit.
How to choose Grapefruits: Look for firm grapefruit that yields slightly when pressed. Avoid overly hard grapefruit as this is a sign of drying, and avoid overly soft grapefruit with a sharp pungent smell as this is a sign of rotting.
How to store Grapefruits: Grapefruits can be stored in the refrigerator and will last 2-3 weeks.
Climate and origin: Grapefruits are thought to have originated in Barbados as a cross between an orange and a pomelo. Today grapefruits are grown in tropical climates around the world. (Zone 9-10 in the U.S.)
Taste: Grapefruits have a tart acidic taste with a juicy texture.
Miscellaneous information: The seeds of the grapefruit are very high in antioxidants and may have anti-microbial properties.