What is Endosperm?
Endosperm is the food warehouse inside a seed. It stores the starch, oils, and proteins that fuel the embryo's growth during germination and early seedling development. In some species the endosperm persists in the mature seed; in others, it is absorbed by the embryo before the seed is shed.
Formation
Unique to flowering plants (angiosperms):
- Double fertilization: One sperm fuses with the egg (forming embryo); a second sperm fuses with two polar nuclei (forming triploid endosperm).
- Cell division: Endosperm cells rapidly divide and fill with stored nutrients.
- Maturation: In some species, the embryo absorbs the endosperm before the seed matures.
Types
Persistent Endosperm (Albuminous Seeds)
Endosperm remains in the mature seed:
- Coconut: Liquid endosperm (coconut water) + solid endosperm (coconut meat).
- Coffee: Endosperm is what we roast and brew.
- Palms: Many palm seeds have hard, oily endosperm.
Absorbed Endosperm (Exalbuminous Seeds)
Embryo absorbs the endosperm before maturity:
- Beans and legumes: Cotyledons contain all the stored food.
- Mango: Large cotyledons provide all germination energy.
Costa Rican Examples
Coco (Cocos nucifera)
The largest and most familiar endosperm — coconut water and meat are endosperm tissue.
Coffee (Coffea arabica)
The endosperm of the coffee seed is what is dried, roasted, and brewed — the "bean."
Pejibaye (Bactris gasipaes)
Oily, starchy endosperm made this palm the staple food crop of pre-Columbian peoples.
Why It Matters
- Agriculture: Endosperm is the basis of most human food (rice, wheat, corn are all endosperm).
- Propagation: Adequate endosperm is critical for successful seed germination.
- Ecology: Seed size and endosperm reserves affect seedling establishment strategy.