The largest flower in the world, Rafflesia arnoldii, is more than three feet across. With no roots, shoots, stems, or leaves, this parasitic plant is stealthy, visually undetectable until it prepares to bloom.

Buds erupt without warning from an infected host vine and swell slowly over months to the size of cabbages. In full bloom, each bud’s central floral chamber—orb-shaped, with a circular opening at the top—resembles a planetarium or astronomical observatory with a mottled roof partially opened to the sky.

Within lies a disk covered with spiked structures. Botanists have named the spikes “processes,” but have no clear idea what they do. In the largest flowers, the chamber is almost big enough for an infant to crawl inside and fall asleep.