There’s a puzzle on Lord Howe Island. It’s less than 15km² (6 square miles) of land in the Tasman Sea. On it are two species of palm, Howea forsteriana and H. belmoreana. H. belmoreana is more successful on volcanic soil than its neighbour, but H. forsteriana is able to live on the calcareous soil of the island while H. belmoreana, for some reason, cannot.

The soils aren’t zoned so one side of the island is one type and the other half is another. The soil types are speckled across the island. Also, palms are wind pollinated. There’s no pollinator that an innovator can attract that doesn’t help the other tree. So, if the island was colonised by an ancestral Howea palm, how did speciation happen? This is the problem explained and tackled by Osborne et al. in a new paper in New Phytologist Arbuscular mycorrhizal fungi promote coexistence and niche divergence of sympatric palm species on a remote oceanic island.