The migration of plants from water to newly emerged land some 450 million years ago required plants to acquire a number of crucial new traits. Fossil records provide compelling evidence that one of these traits is the symbiosis (or mutualism) between these early land plants and arbuscular mycorrhizal (AM) fungi. On page 864 of this issue, Rich et al. (1) show that the primitive land plant Marchantia paleacea produces lipids that are transferred to the fungus and that this process is essential for a functional symbiosis (see the image). This localized lipid biosynthesis also occurs in higher plants that engage in symbiosis with AM fungi (2, 3), but not in algae, suggesting that this process evolved 450 million years ago, allowing plants to colonize land, and is conserved across the plant kingdom.