Phylogeny of the subtribe Asterinae (Asteraceae: Astereae): new circumscription for Asterinae and Aster and implications for pappus evolution

BACKGROUND: The subtribe Asterinae (Asteraceae: Astereae) comprises ∼300 species across 13 genera (including the well-known type genus Aster) with considerable horticultural and ecological importance. The pappus, a key character for dispersal and protection, is highly diverse and taxonomically important in Asterinae. However, the phylogenetic relationships within Asterinae and Aster remain poorly resolved, leading to persistent taxonomic controversies and obscuring the evolutionary history of the pappus morphology. METHODS: We reconstructed both plastid (using five newly developed markers) and nuclear (using 130,503 SNPs generated from ddRADseq) trees, based on a comprehensive sampling of 119 species representing all 13 genera of Asterinae and allied subtribes. Using these newly obtained trees, we inferred the evolutionary trajectories of pappus morphology across Asterinae. KEY RESULTS: Both plastid and nuclear SNP trees resolved relationships within Asterinae with strong support. The previously defined Asterinae and Aster were revealed to be polyphyletic, splitting into four (plastid tree) or seven (nuclear SNP tree) clades, respectively. Both trees strongly supported a large clade containing most genera and species of the previously circumscribed Asterinae. Within this large clade, four consistent and highly supported subclades were recovered, while three additional clades were resolved outside of it. Incongruent placements of several taxa between the two trees were detected. Ancestral state reconstruction revealed extensive homoplasy in pappus evolution, undermining taxonomic reliability of the pappus morphology. CONCLUSIONS: We redefine Asterinae to include only its core clade and recognize a single monophyletic Aster. This revised taxonomy of Asterinae consolidates 16 former genera of Astereae. Additionally, we propose one new subtribe (Chlamyditinae) and four subgenera within Aster-three of which are novel. This framework clarifies the taxonomy of Asterinae and Aster and lays the groundwork for future studies on the evolution of pappus and other characters that may drive the rise of its remarkable species diversity.