Rafflesia Arnoldii, the world’s largest flower. Diameter of about one meter and weighing up to ten kilograms. It's rare & not easily located, growing once a year, blooming for 5 days. Found in Indonesian rain forests of southeastern Asia and Philippines.
Titan Arum - Amorphophallus Titanum - the plant with the largest unbranched inflorescence in the world - Also known as the "carrion flower," corpse flower, or corpse plant because of its odor (Top 10 Rare & Unusual Flowers)