On two small islands in the Indian Ocean, an endangered palm with the world's largest seed

Even trees well-known to science have mysteries. One is the Seychelles' endangered coco de mer, or sea coconut palm tree, which is now relegated to parts of two small Indian Ocean islands and in decline. Only some 8,200 individuals remain.

What Lodoicea madivica lacks in range it makes up for in size, which frankly made it very hard for scientists—or anyone—to miss. Its seed can weigh up to 18kg. (Some reports say even heavier.)

The seed's size and "suggestive" shape probably made it popular with collectors and royal courts hundreds of years ago (the is named after Louis XV of France). To this day, seed poaching for black market demand is a menace to the palm's continued existence.

It takes a phenomenal tree to make a phenomenal seed, so it is little wonder the biology of the giant palm tree is fascinating. The coco de mer's latest surprise, published in Scientific Reports, is that inbreeding doesn't appear to be among its , unlike many across the plant and animal kingdoms.

A male coco de mer palm (Lodoicea maldivica) towers above the canopy on Curieuse Island, Seychelles. Credit: Chris Kettle/Alliance Bioversity-CIAT

Coco de mer (Lodoicea maldivica) seeds in Vallee de Mai, Seychelles. Credit: Chris Kettle/Alliance Bioversity CIAT

Male inflorescence of a coco de mer palm (Lodoicea maldivica). Alliance researcher Chris Kettle for scale. Credit: Emma J. Morgan/ETH Zürich