No, the basal taxon and the outgroup in a phylogenetic tree are not the same, although they are related concepts in evolutionary biology.
The basal taxon refers to a lineage that diverged early in the history of a group and typically lies at or near the base of a phylogenetic tree. It serves as a reference point for understanding the evolutionary relationships among other taxa in the tree.
On the other hand, the outgroup is a taxon that is not part of the group being studied (the ingroup) but is closely related enough to provide insight into the traits and characteristics of the ingroup. The outgroup is used to help determine the direction of evolutionary changes.
In summary, while both the basal taxon and outgroup can help in analyzing evolutionary relationships, they have different roles and are not synonymous. The basal taxon is part of the ingroup and represents an early branch, while the outgroup is external to the ingroup, providing a comparative framework.