Sticking with my original answer, the largest orchid is Grammatophyllum speciosum
The dramatic six-foot flower spikes emerge from the pseudobulb bases. Over a two-month period, each prodigious spike may produce a hundred large, waxy flowers, four inches in diameter and mottled reddish brown and butterscotch yellow.
As a matterer of interest:
Largest flower of all are the Parasite stinking corpse lily (Rafflesia arnoldii), which can grow to 91 cm 3ft wide, 1.9 cm ¾in thick and weigh up to 7 kg 15 lb. The plants attach themselves to cissus vines in the jungles of South-east asia and, true to name have an extremely offensive scent.