Tiny mosses were the first land plants to evolve on Earth. But the first real plants, the big leafy kind, came on the scene 400 million years ago—200 million years before hardwood trees and flowering plants.

I’m talking about ferns.

They flourished, then and now, through a unique two-stage life cycle.

Mature ferns produce spores that drop to the ground. There they grow into gametophytes, which don’t look anything like the mature example. In some species, they grow underground.

The gametophytes produce eggs and sperm—which require water to swim and find other eggs. Once they unite, they grow into a fern.

Most fern species produce rhizomes, or root runners, which send up the fronds. When fronds die from cold or age, the rhizomes produce more.

Early ferns soon developed many forms. They grew on dry land, in swamps, even in water. They were tiny and huge: tree ferns grew woody trunks and reached 25 feet in height.

By 300 million years ago, Earth was covered in forests of ferns. But a changing climate, and eventual competition from other plants, made many species go extinct.

Still, ferns flourished. Today, they’re the second most diverse type of plant on Earth with more than 10,000 species.

Including one with a surprising behavior—which we’ll talk about on another EarthDate.