<p>Ecotones harbour multiple plant taxa under similar macroclimate conditions but differing microscale environments, often reflecting ancient biogeographic processes. Here, we evaluated plant communities’ phylogenetic composition, structure, and dissimilarities within diverse vegetation types in forest-grassland mosaics. The study took place in two state parks in Paraná state, Brazil. We used plant community data surveyed in different vegetation types of grasslands and forests (i.e., dry, rocky, and wet grasslands, forests, and tree-encroached grasslands). We computed alpha phylogenetic diversity for each vegetation type and partitioned beta phylogenetic diversity into turnover and nestedness of lineages. Then, we compared all observed values with null expectations from the regional lineage pool. Furthermore, we assessed the distribution of plant clades across the vegetation types. Grasslands exhibited lower alpha phylogenetic diversity than forests. More specifically, wet grasslands displayed higher phylogenetic clustering than rocky and dry grasslands. In contrast, forests and their adjacent tree-encroached grasslands only differed in the extent of phylogenetic composition, not its structure. Phylogenetic beta diversity was higher when other vegetation types were compared to grasslands. We found high lineage turnover among vegetation types. Ferns are associated with tree-encroached grasslands, while eudicots are more linked to woody communities, including dry grasslands. Given the different ages of prominent lineages in forests and grasslands, the association of lineages with vegetation types underscores an enduring impact of eco-evolutionary conservatism in traits at varying depths in evolutionary history. Our findings show that phylogenetic divergences among ancient lineages leave a historical imprint on present-day vegetation patterns in forest-grassland mosaics.</p>