The seed

Elkinsia polymorpha from West Virginia is among the oldest seed plants. The seed solves three problems at once: fertilisation without free water, protection of the embryo, and nourishment for germination. Together with pollen — which lets male gametes travel by wind rather than swim — it decoupled plant life from moisture. The consequence was that continental interiors, until then largely bare, could turn green. All conifers and flowering plants, and therefore all grain, fruit and grass, build on this invention.