India, March 28 -- The world's oldest known flower looked nothing like a bloom. It was vine-like, with no petals, and resembled a weed or herb.

The Montsechia vidalii thrived deep in Europe's lakes, in the Cretaceous period, about 130 million years ago. Fossils discovered in Spain in 2015 confirmed that it had no nectar-producing features. What it did bear was fruit. Each bud contained a tiny seed.

There remain a host of strange flowers, among the 400,000 known species in the world.

Some are straight out of a horror movie: parasites that burst forth from a vine. Others seem woven out of fantasy: translucent white ghosts, or blooms born of fire. Take a look.

A key to the future: The tiny, purple Dicliptera polymorpha

This plant, which...