Which parasitic plant produces the world's largest individual flower, up to 1 meter across?

The parasitic plant that produces the world’s largest individual flower, reaching about 1 meter across, is Rafflesia arnoldii.

Rafflesia arnoldii is native to the rainforests of Sumatra and Borneo. It is an extreme holoparasite: it has no visible leaves, stems, roots, chlorophyll, or independent photosynthetic system. Most of its body remains embedded inside vines of the genus Tetrastigma, absorbing water and nutrients from the host. The plant becomes conspicuous only when its enormous flower emerges.

The flower’s reddish-brown surface is marked with pale spots, and its smell resembles rotting flesh. That odor attracts carrion flies, which act as pollinators. Flowers are generally either male or female, so successful reproduction requires insects to transfer pollen between separate blooms. A bud may take many months to develop, while the open flower lasts only a few days.

A frequent mix-up involves the titan arum, or Amorphophallus titanum. It can produce a taller and more spectacular flowering structure, but that structure is an inflorescence made of many tiny flowers. Rafflesia arnoldii holds the better-known record for the largest single flower.