Coconut biology

Both the Largest Drupe and the Largest Seed in the World

The shiny outer skin of a coconut is called the exocarp. Six- to eight-month-old coconuts are usually green, and turn yellow to orange when they ripen.
The coconut is a drupe. Unlike other drupes such as plums or cherries, the actual pulp of the fruit isn't edible, but its stringy texture makes it ideal for rope-making, for example. The part of the coconut that we actually consume is the inside of the drupe's pit.
This pit (endocarp) encompasses the nutritive tissue (endosperm) and the seed of the coconut. The pit, i.e. the endocarp, has two phases - one solid, one fluid. Hidden away within the coconut flesh lies the tiny, almost unpercievable coconut embryo. During germination, however, the embryo swells up to such an extent that it fills out the entire inside of the fruit. Fun fact: in many tropical countries, the coconut embryo is considered a delicacy.
Coconut cross-section:
Coconut cross-section