basal

Basic, elementary; relating to, or forming, the base, or point of origin.

This is the basal idea.

The organism needs more energy on basal maintenance.

Associated with the base of an organism or structure.

In the spring, basal leaves emerge from a stout taproot.

Of a minimal level that is necessary for maintaining the health or life of an organism.

a basal diet

In a phylogenetic tree, being a group, or member of a group, which diverged earlier. The earliest clade to branch in a larger clade.

Hittite is a basal Indo-European language.

A magnolia is a basal angiosperm.

base, bottom, minimum

Any basal structure or part