Format: ORAL

Pakkapol Thaowetsuwan1, Ricarda Riina2, Louis P. Ronse De Craene3

1 Department of Biology, Faculty of Science, Silpakorn University, Nakhon Pathom, Thailand 2 Real Jardín Botánico (RJB) CSIC, Madrid, Spain 3 Royal Botanic Garden Edinburgh, Edinburgh, United Kingdom

The tribe Crotoneae comprises six genera Sandwithia, Sagotia, Acidocroton, Astraea, Brasiliocroton and the mega-diverse Croton. However, there is no prior study compares floral morphology across all six genera except in few species of Astraea and Croton. To understand the floral diversity in this tribe, inflorescences and flowers from at least one species from each genus were examined with various techniques, e.g., light microscopy, scanning electron microscopy, resin sectioning and micro-CT. Our investigation revealed significant floral diversity among all genera. Our investigation further identified several synapomorphies across the Crotoneae tribe, including the exclusive presence of staminate flowers on the upper portion of the inflorescence, the presence of more than 10 stamens in staminate flowers, and the reduction of petals in pistillate flowers. Furthermore, synapomorphies of each subclade within the Crotoneae were identified. The Sagotia-Sandwithia clade members have botryoid inflorescences, simple trichomes, petals exceeding the size of sepals at the anthesis, and outermost stamens alternating with petals. In contrast, the Acidocroton-Astraea-Brasiliocroton-Crotonclade exhibits racemose inflorescence, stellate trichomes with diverse forms, and outermost stamens positioning opposite petals. Notably, Acidocroton, despite belonging to this clade, exhibits some unusual characters that diverge from the typical patterns observed within the group. Our investigation also explored and discussed the inflorescence and floral morphologies of the Crotoneae compare to the tribe Jatropheae and others groups in the subfamily Crotonoideae. Therefore, our study highlights the remarkable heterogeneity present among members of this tribe and provides valuable insights into the key morphological features that define the entire group. Further research is needed to fully elucidate the complex evolutionary relationships and adaptive significance of floral characteristics within the Crotoneae.