The Coco de mer (Lodoicea maldivica (J. F. Gmelin) Persoon, Arecaceae) is a palm tree that grows on the islands of Praslin and Curieuse in the Seychelles. It is the sole member of the genus Lodoicea.

Its fruit, weighing up to 22 kg and measuring up to 50 cm across, contains the double coconut, which is the largest seed in the world, and is so called because it has two lobes each resembling a coconut. It is an example of a sea-bean or drift seed, which is a seed that is designed to be dispersed by the sea. It is also called the coco fesse, sea coconut and Seychelles nut.

The sailors who first saw the double coconut floating in the sea imagined that it resembled a woman's disembodied buttocks. This fanciful association is reflected in one of the plant's archaic botanical names, Lodoicea callypige Comm. ex J. St.-Hil., in which callipyge is from Greek words meaning 'beautiful rump'. Other botanical names used in the past include Lodoicea sechellarum Labill. and Lodoicea sonneratii (Giseke) Baill. Until the true source of nut was discovered in 1768, it was believed by many to grow on a mythical tree at the bottom of the sea. The coco de mer is now a rare protected species.

The genus name is from Lodoicus, the Latinised form of Louis, in honour of King Louis XV of France.