The mode of speciation characteristic of a single evolving lineage of species is referred to as "anagenesis." Anagenesis is a gradual process in which genetic changes accumulate over time, leading to the formation of new species within the same lineage. It does not involve branching or the formation of separate lineages. Instead, it represents a continuous transformation of a species into a different species without the formation of distinct branches or offshoots. Anagenesis is often contrasted with "cladogenesis," which involves the branching and diversification of lineages, resulting in the formation of multiple new species.