hypogeal
adjective
hy·po·ge·al ˌhī-pə-ˈjē-əl 
variants or hypogean
ˌhī-pə-ˈjē-ən
or hypogeous ˌhī-pə-ˈjē-əs
1
: growing or living below the surface of the ground
2
of a cotyledon : remaining below the ground while the epicotyl elongates
Word History
Etymology
Late Latin hypogēus, hypogaeos "underground, subterranean" (borrowed from Greek hypógeios, hypógaios, from hypo- hypo- + -geios, adjective derivative of gê "earth" and -gaios, adjective derivative of gaîa "earth") + -al entry 1, -an entry 2, -ous — more at geo-
First Known Use
1686, in the meaning defined at sense 1