Plant Story--Double Coconut, World's Largest Seed

In April 2018, I visited Foster Botanical Garden in Honolulu, Hawaii, and saw this:

Double coconut (Lodoicea maldivica) seed, April 2018

A cage around a very large seed.

It was the double coconut, also called coco de mer (sea coconut), and Seychelles coconut, the largest seed in the world. Largest seed in the world!--of course I was interested. It is the seed of the palm Lodoicea maldivica (palm family, Arecaceae), a very rare plant endemic to the Secheylles. (Lodoicea is Latin for Louis, honoring King Louis XV of France, maldivica is because it was thought, incorrectly, to come from the Maldives.)

This post, Plant Story--The Double Coconut, is about the plant. The next post, Playing Cupid for the Double Coconut, gives the story behind the seed in the cage in 2018 and what I saw on my return  in 2019.

The double coconut is a relative of the coconut (Cocos nucifera), but its seed is bigger and heavier than a coconut. Like a coconut, the fruit has a tough, green exterior. On the palm, it looks like a large coconut. Inside, however, where the hairy, brown coconut (which is a seed see diagram), is round like a bowling ball, the double coconut is--you guessed it--double, that is, with two lobes. (See photos).

Double coconut seed in Honolulu.
The angle in my photo is difficult. It is actually 3x the length of the camera case.
The leaves by the seed are from a lawn weed; there is no sign of life.
The fence is to keep rats from eating the seed.

The double coconut seed is the largest in the world, 12 inches long and usually weighting 44 pounds (20 kg). The largest one recorded was 55 pounds (25 kg). The coconut--the second largest seed in the world--is 6" long and a maxiumum of 8 pounds (3.6 kg), so the double coconut is in a size class by itself.

The double coconut fruit, containing the seed, is the largest wild fruit in the world. Usually there is only one seed per fruit, but two and more rarely three have been recorded, making the fruit weight up to 100 pounds (45 kg). Very dangerous when it falls.

(For the record, the world's largest fruit was produced by the pumpkin, Cucurbita maxima (cucumber family, Cucurbitaceae). People have bred ever larger pumpkins: in 2019 the world record was 2,624 pounds, set in 2016 link . It is an ongoing competition.)

Not only is the double coconut remarkable because of its size, it is native only to the Seychelles, map archipelago in the Indian Ocean of 155 islands and atolls, 900 miles from east Africa and farther from anywhere else. The islands were uninhabited until colonized by the French in the 1750s, although ships occasionally stopped before that, going back before the Christian Era. The double coconut palm is only found on two of the islands within the Seychelles, and the plant was unknown to the outside world before the 1750s. But the fruits, or rather, their husks--the ripe fruit does not float--sometimes drifted to the shores of Africa and India. They were large; they were amazing. You could see detailed female anatomy in the shape (Google link ) so the husks became religious and high status objects in Africa and across Asia. When they reached Europe, they were decorated as cups and bowls  (See gold-decorated ewer made from a double coconut, British Museum, 1575-1600 link).

And where did these amazing husks come from? Europeans imagined that they were the fruit of undersea palms, which resulted in the name coco de mer. Double coconut is the usual common name today since it is easier for English speakers. I think we could call it the Seychelles coconut, a name you see occasionally.

Furthermore, they aren't "sea coconuts" because healthy fruits and seeds are too dense to float. Double coconuts do not float across oceans, instead, they disperse poorly, which is why they are confined to two islands in an archipelago of 155.

 leaves

As the big seed suggests, double coconuts are big plants, growing to over 180 feet tall, though most living individuals are about 100' high. Their leaves are huge, 35-45 feet long. They grow slowly and are thought to live many years, but since they have only been known to western science since 1750s, we know they can live 270 years but are only guessing beyond that. (As palms, they are not trees, do not have wood, and so make no rings that can be used to determine age. Neat stuff on palms: link).

The double coconut is dioecious: one plant makes pollen while another develops the seed, so to produce fruit, two plants of opposite sexes are needed. That is another problem for the spread of the plant since at least two plants are needed on the new site if they are to reproduce. In contrast, coconuts have male and female flowers on the same plant, so are much better at colonization.
Double coconuts do not flower until they are about 25 years old, but once in flower, males in particular, continue to flower for months. In addition to having seeds that look like the genitalia of women, the stalk (inflorescence) of male flowers is strikingly phallic (photos). Pollination is not well-understood; different experts have different opinions.

double coconut, Lodoicea maldivica, in Honolulu

After pollination, the fruit takes up to seven years to ripen. Like coconuts, the inside of the seed starts as a liquid and slowly solidifies. After it ripens and falls to the ground, it may be two years before the seedling first emerges from the seed, partly because the fruit has to rot off of the seed. The seed first sends out a seedling root (radicle), 1 inch in diameter. The radicle can run across the forest floor for 30 feet (10 m) searching for a good location before descends into the soil to form the new root system. When a good root system is established, as much as two years later, the seed sends up its first leaf. The nutrients in the seed may feed the seedling for five years.

This is a rare plant, with a few thousand plants in their native forest, confined to two islands. Furthermore, double coconut palms dominate in their forests and a number of endemic animals--gekkos, snails--are found only in their canopies.

Conservation is difficult because the seeds are so attractive to humans. They command a high price, being wanted for their size, for their shape, but also because, like coconuts, the flesh ("ivory") within the developing seed is tasty and nutrious. But if you eat that, there will be no seedling. The plants, fruits, and especially the seeds are protected by the Seychelles government, but poaching continues. After the seedling no longer needs them, the old seed husks, like a the round woody coconut hull only bigger and double, are still valuable and the government of the Seychelles regulates their sale.

Around the world, botanical gardens have tried to grow double coconuts and, once they have plants, to produce additional seeds. That was why Foster Botanical Garden in Honolulu had seeds in cages in 2018. In the next post, Playing Cupid to the Double Coconut, I'll describe some of the challenges of crossing rare palms.

The mother palm in Honolulu, and in the background, a seed protected by a cage

Comments and corrections welcome.

Note: Two other records have been claimed for the double coconut: largest male inflorescence (stalk with flowers), more than 3' long (1 meter) and thick as a man's arm; and largest female flowers of any palm. Both seem likely but I haven't checked carefully.

Sources

Blackmore, S., S-C. Chin, L.C. Seng, F. Christie, F. Inches, P. W. Utami, N. Watherston and A. H. Wortley. 2012. Observations on the morphology, pollination and cultivation of coco de mer (Lodoicea maldivica (J F Gmel.) Pets., Palmae). Journal of Botany. link Accessed 01/04/20.
Gerlach, J. 2014. Seychellia lodoiceae . The IUCN Red List of Threatened Species 2014: e.T196295A2443318. http://dx.doi.org/10.2305/IUCN.UK.2014-1.RLTS.T196295A2443318.en. Accessed  01/06/2020.
Gollner, A. L. 2008.The Fruit Hunters. Scribner, New York. Chapter on The Lady Fruit (double coconut) highly recommended. 
Hodgson, L. 2018. The Double Coconut: The World's Largest Seed. Laidback Gardener Blog. 
link  Accessed 01/07/20.

Kathy Keeler, A Wandering Botanist

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