Format: ORAL

Eve Lucas1, Max Fontaine1,2, Low Yee Wen1,3, Wei Han Fang4, Matilda Brown1

1. Royal Botanic Gardens Kew, Richmond, Surrey, UK 2. University of Bath, UK 3. Singapore Botanic Gardens, 1 Cluny Road, Singapore 4. National Taiwan University, Taipei, Taiwan

Syzygium (Myrtaceae), is one of the most diverse tree genera globally, encompassing economically significant species such as clove, lilly pilly, and water apple. Its natural habitat spans Southeast Asia, Southern Asia, Australia, and the Pacific, with most species falling within Syzygium subgenus Syzygium. Despite its economic importance, the taxonomic complexity of the genus, coupled with limited knowledge about its evolution and ecology, poses challenges to downstream activities such as conservation. Our study focuses on a representative sample of Syzygium subgenus Syzygium, leveraging reproductive traits, geolocation data, and climate information. Our aim is to identify the key environmental variables influencing floral and fruit diversity within the genus. Considering the relationships among biotic and abiotic factors, we explore these variables within a phylogenetic context to discern patterns independent of and influenced by the environment. Our investigation recorded 12 continuous and 13 discontinuous traits related to flowers and fruits from the sample species. To analyse climate variation, we extracted 19 CHELSA bioclimatic variables for all GBIF Syzygium occurrences. Mixed PCA plots were constructed to independently assess trait and environmental Principal Components. To understand the evolution of each trait cluster, we compared Brownian Motion and Ornstein-Uhlenbeck models of evolution based on a pruned version of the most comprehensive available phylogenetic hypothesis. Phylogenetic linear modelling was employed to observe the interplay between the environment and the main axes of trait variation while considering the evolutionary relationships between species. Our results highlight temperature, precipitation, and seasonality as the primary independent climatic drivers influencing Syzygium distribution. We found that flower/fruit size contributes more to morphological variation than any other biotic traits examined. Weak correlations were identified between flower/fruit size, inflorescence architecture, fruit colour, and climate. All biotic traits better fit the Ornstein-Uhlenbeck model suggesting that these characteristics are evolving under natural selection rather than randomly.