In-situ diversification and regional attributes shape asymmetric diversity of Miliusa (Annonaceae) in tropical Asia.

Aim: We examine biogeography and speciation patterns in Miliusa Lesch. ex A. DC. (~65 species) distributed in tropical Asia to understand its uneven diversity in tropical Asia. Location: Tropical Asia Taxon: Miliusa (Annonaceae) Methods: Phylogenetic reconstruction was done using six plastid markers across 52 species using ML and BI approaches. Divergence time was estimated using two fossil calibrations and an optimised relaxed clock, and ancestral areas were inferred with BioGeoBEARS. Speciation rates were examined using ClaDS and the DR statistic, and the community structure was assessed using phylogenetic diversity metrics. Results: Miliusa likely originated in the mid-Miocene, with Indo-Burma and peninsular India (PI) as its ancestral range. Extant diversity is primarily attributed to in-situ speciation, with dispersal or vicariance playing limited but important roles in PI, and Wallacea and Sahul. Indo-Burman lineages began accumulating in the mid-Miocene in contrast to PI (~10 Myr) and Wallacea and Sahul (~5 Myr). PI shows signs of lineage saturation and had lower speciation rates than Wallacea and Sahul and Indo-Burma, which had similar rates. All regions exhibited phylogenetic clustering, but Indo-Burma and PI differed in sensitivity to phylogenetic depths. Main conclusions: The uneven diversity of Miliusa is shaped by time for speciation, age, and dispersal, although their relative influence varied across regions. In Indo-Burma, long-term geo-climatic stability and greater niche availability likely facilitated the persistence of lineages, rapid speciation, and dispersal, making it an evolutionary hotspot for Miliusa. In contrast, the PI had lower richness and speciation rates despite being older, due to contraction of wet habitats limiting the available niches for speciation. Lineages in Wallacea and Sahul show typical island-like radiations with speciation rates comparable to larger and more stable Indo-Burma, despite being young. Overall, our results highlight the role of Miocene-driven climatic vicariance and Pliocene-Pleistocene climatic fluctuations in shaping the diversification dynamics and diversity patterns in tropical Asia. Keywords: biogeography, diversification, peninsular India, speciation, tropical Asia, Western Ghats, woody plants