We got a lot of good guesses for this one, including pumpkin and avacodo seeds. But the answer is the seed of the double coconut or coco de mer (Lodoicea maldivica) The seed, which can take up to 10 years to develop, can weigh over 20 kilograms! While one of our readers saw this palm at Kew Gardens in England (one of the world’s major botanical gardens), it is a native of the Seychelles, a group of islands in the Indian Ocean off the east coast of Africa.