An apomorphy is a derived characteristic of a clade - any feature which is unique to a base species and its descendants.
First organism and all descendants First organism all descents to have an apomorphy as found in the internal specifier.
In evolutionary biology, plesiomorphy refers to ancestral traits shared by a group of organisms, while apomorphy refers to derived traits that are unique to a specific group of organisms. Plesiomorphies are characteristics that are inherited from a common ancestor, while apomorphies are evolutionary innovations that distinguish one group from another.
The term used to indicate a relatively new characteristic in an evolutionary sense is "derived trait" or "apomorphy." These traits are distinct from ancestral characteristics and arise as species evolve, helping to differentiate them from their predecessors. Derived traits are often used in the context of phylogenetic analysis to understand evolutionary relationships among organisms.