The concept that refers to all the evolutionary innovations shared by a recent common ancestor is known as synapomorphy. Synapomorphies are traits that are derived and shared by a group of organisms, indicating that they have a common evolutionary origin. This term is critical in cladistics, which is a method of classifying species based on common ancestry.
When a recent common ancestor possesses certain innovations, the descendants of that ancestor will share those traits, which can include structural, genetic, or biochemical characteristics. Identifying these shared derived characteristics helps in constructing evolutionary trees and understanding the relationships among different species.
In contrast, the other terms have distinct meanings that do not directly address the concept of shared evolutionary innovations among descendants. Plesiomorphy refers to ancestral traits that may not be unique to a particular group. Homologous evolution typically speaks to the presence of similar traits due to shared ancestry, but it does not encompass the idea of shared innovations as precisely as synapomorphy. Taxonomy is the science of naming and classifying organisms, without necessarily focusing on the shared derived traits that define evolutionary relationships.