hypogeal

Hypogeal is a botanical term describing a mode of seed germination in which the cotyledons stay below the soil surface as the seedling emerges. The word comes from Greek hypo- meaning under and ge meaning earth. In hypogeal germination, the growing point of the shoot (the plumule or epicotyl) grows upward while the cotyledons remain underground, often acting as a storage tissue during early development. This contrasts with epigeal germination, where the cotyledons are raised above the ground as the seedling emerges.

In a hypogeal germination process, the radicle typically forms first to establish the root system, and the shoot develops beneath the surface until it reaches light. Because the cotyledons stay underground, they are sometimes protected from herbivory and desiccation, and the seedling relies on stored reserves within those cotyledons until true leaves become photosynthetic.

Ecological and horticultural notes: Hypogeal germination can be advantageous in certain environments, such as where soil moisture or protection from above-ground threats favors delayed cotyledon emergence. It also influences how seeds are stored and how seedlings are grown in cultivation, including considerations for soil depth and light exposure during emergence.

Examples: A classic example of hypogeal germination is the pea (Pisum sativum). Other legume species also exhibit hypogeal germination, though germination modes can vary across taxa.

See also: epigeal germination, seed germination, plant development.