Vascular plants (Cooksonia)

Vascular plants are plants with internal pipes. They have a tissue called xylem that carries water and minerals upward, and phloem that carries sugars around the body. Among the earliest known examples is Cooksonia, a plant about 432 million years old from the Silurian period. It stood only a few centimeters tall and had no leaves or roots, just thin forked stems, each tip ending in a tiny spore capsule. It was named for the Australian paleobotanist Isabel Cookson, and its fossils are known from places such as Wales, Ireland and Czechia.

Before this, land plants such as mosses and liverworts had no real plumbing. They soaked up water directly, which kept them small and tied to damp ground. The key innovation was a stiff, water-conducting cell called a tracheid, reinforced with a tough substance called lignin. Lignin lets the pipes resist collapse as water is pulled upward by evaporation, and it also makes stems strong enough to stay upright.

Standing upright gave a big advantage in the contest for sunlight and for spreading spores on the wind. Over the next 50 million years, vascular plants evolved roots to anchor and feed, leaves to catch more light, and finally true trees. By about 385 million years ago, they had formed the first forests. Scientists note that Cooksonia itself is a fossil group that may not be a single family, and some specimens lack clear evidence of vascular tissue, so its role is debated, but the move to plumbing is well established.