the world > plants > by growth or development > defined by habit > tree or woody plant > characterized by habitat > [adjective] > buried in the earth (2)
subterranean1610
Of a tree, forest, etc.: buried in the soil or other deposits in a fossilized or otherwise preserved form. Now chiefly historical.
subterraneous1673
Of trees, a forest, etc.: buried in the ground; = subterranean, adj. 1c. Obsolete.