hy·po·ge·al 
(hī′pə-jēəl) also hy·po·ge·an (-ən) or hy·po·ge·ous (-əs)
(hī′pə-jēəl) also hy·po·ge·an (-ən) or hy·po·ge·ous (-əs)adj.
1. Living or occurring under the earth's surface.
2. Botany Of or relating to seed germination in which the cotyledons remain below the surface of the ground.
[From Latin hypogēus, from Greek hupogeios : hupo-, hypo- + gē, earth.]
hy′po·geal·ly adv.