The coconut is, although it may not seem like it, one of the strangest fruits. The spherical-looking piece that we find on the market is, in fact, the stone of a fleshy drupe-type fruit, of the same type as peaches or olives. However, the pulp is not as juicy as that of these fruits.
The coconut palm can reach 30 meters in height, with long, divided leaves up to 5 meters in length. It presents a smooth stem, constituted by the dry sheaths of the leaves —it does not form true wood—.
Its roots are also fibrous, with a system of abundant adventitious roots —up to 4,000— that start from the base of the stem and grow outwards, near the surface, and few roots directed downwards. These roots are thin and fragile, although the plant constantly replenishes them.
The flowers develop in a dense inflorescence, the female flowers open first, and the male ones later. Normally, until the first ones have closed, the second ones do not open, which helps to avoid self-fertilization . Except for exceptions, in which the male flowers open before the female ones of the same inflorescence close, and, therefore, fertilization with the same individual is possible.
Pollination occurs by the action of wind or insects. When the female flowers are fertilized, a fruit will develop from each of them .
A coconut fruit can weigh up to a kilo and a half. The thick, yellow or greenish skin forms the epicarp of the fruit; below is the mesocarp , formed by firm fibers densely intertwined with each other, generating a spongy tissue. These fibers are used in some places as a fertilizer , not only because of the large amount of nutrients it brings to the soil, but also because of its ability to adsorb water.
Below these fibers is the endocarp , hard, leathery, which protects the seed it contains inside. This endocarp is, in fact, the shell of the coconut that we find in the store. It has three circular slits at its end, called micropyles , two of them blind, and another functional. Beneath it, the tiny embryo is anchored.
Going even deeper below that shell, there is a thin brown skin about 4 or 5 millimeters thick, which is the seed coat, and inside it, the edible part of the coconut, the endosperm , which has two phases, one solid, white and fleshy, and the other liquid and aqueous, which is commonly called “coconut water”.
A particularity of the coconut seed is that it is not completely filled with “coconut water”, but only a small part of its volume. The rest is filled with air . Furthermore, the mesocarp, that spongy layer of intertwined fibers, also has multiple air chambers, and is adequately insulated by the epicarp, the thick yellow or greenish skin.
The sealed chamber that makes up the epicarp of the coconut prevents seawater from infiltrating; This peculiarity not only allows it to float in the water, but also protects the seed from salinity. And that is, mainly, its propagation route: the ability to float in the sea. Palm trees often grow near the beach, and when the coconut falls, it rolls downhill into the water, where it is swept away by currents, facilitating its dispersal from one island to nearby islands .
The great thickness of the endocarp, that hard and leathery shell, significantly delays germination, protecting the embryo. It can survive more than 120 days drifting . Upon reaching solid ground, the epicarp decomposes and the spongy mesocarp retains moisture, favoring rooting. Let us remember that these fibers are used as fertilizer; when it breaks down, it will nourish the seedling once it germinates.
Once the embryo germinates, it crosses the endocarp through the functional micropyle and anchors itself in the ground on the beach, where, if all goes well, it will give rise to a new palm tree.
Referencias:
Chan, E. et al. 2006. Cocos nucifera (coconut). Species Profiles for Pacific Island Agroforestry, 27.
Edmondson, C. H. 1941. Viability of Coconut Seeds After Floating in Sea. Bernice P. Bishop Museum.
Harries, H. C. et al. 2014. Long-distance dispersal of the coconut palm by migration within the coral atoll ecosystem. Annals of Botany, 113(4), 565-570. DOI: 10.1093/aob/mct293
Ward, R. G. et al. 1992. Special Paper: The Dispersal of the Coconut: Did It Float or Was It Carried to Panama? Journal of Biogeography, 19(5), 467-480.
