Format: ORAL

Jiratthi Satthaphorn1,*, Alan J. Paton2, Wongkot Phuphumirat3, Charan Leeratiwong4

1 School of Science, Walailak University, Thasala, Nakhon Si Thammarat, Thailand 2 Royal Botanic Gardens, Kew, Richmond, Surrey, UK 3 Division of Health and Applied Sciences, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla, Thailand 4 Division of Biological Science, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla, Thailand

Clerodendrum is a highly species-diverse genus belonging to the family Lamiaceae and comprises approximately 250 species distributed in Asia, Australia, and Africa. Systematic studies of the Indo-Chinese Clerodendrum have previously relied on morphological and molecular evidence, while pollen morphology is poorly understood. The palynological evidence has been reported as important for taxonomic resolution for delimiting taxa within Lamiaceae for decades. In this study, pollen morphology of 22 representative Indo-Chinese Clerodendrum were investigated using light and scanning electron microscopy. The results revealed that pollen grains are monad and isopolar or heteropolar in type, subspheroidal to prolate spheroidal in shape and the surface with microechinate ornamentation surrounded by perforations. The apertural types are tricolpate or hexacolpate arranged in two series (trizonocolpate and tricolpate on the proximal pole). The length of the polar axis ranges from 38.14 m to 96.42 m and the length of the equatorial axis is from 31.38 m to 97.72 m and the exine thickness varies from 1.41 m to 3.71 m. Palynological evidence provides insights into detailed micromorphology that can be support phylogenetic relationships of the infrageneric taxa especially species within Clerodendrum section fortunata and Clerodendrum section Tridens. In addition, the results support the distinction between morphologically similar species.