Basal

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

2. (anatomy) Associated with the base of an organism or structure.
3. (medicine) Of a minimal level that is necessary for maintaining the health or life of an organism.
4. (chiefly systematics) In a phylogenetic tree, being a group, or member of a group, which diverged earlier. The earliest clade to branch in a larger clade.

basilar