The world's largest flower

Rafflesia arnoldii, in the Palupuah forest of West Sumatra, Indonesia.  The Wikipedia page has tons of information...

Although Rafflesia is a vascular plant, it lacks any observable leaves, stems or even roots, and does not have chlorophyll. It lives as a holoparasite on vines of the genus Tetrastigma (most commonly Tetrastigma augustifolia). Similar to fungi, individuals grow as a mass of thread-like strands of tissue completely embedded within and in intimate contact with surrounding host cells from which nutrients and water are obtained. It can only be seen outside the host plant when it is ready to reproduce; the only part of Rafflesia that is identifiable as distinctly plant-like are the flowers, though even these are unusual since they attain massive proportions, have a reddish-brown colouration, and stink of rotting flesh. According to Sandved, the flower opens with a hissing sound.

The flower of Rafflesia arnoldii grows to a diameter of around one meter (3.3 feet), weighing up to 11 kilograms (24 lb)

...ecotourism [note the photo] is thought to be a main threat to the species. At locations which are regularly visited by tourists the number of flower buds produced per year has decreased.

Photo credit Adi Prima/Anadolu/Getty Images, via The Guardian.