Taxonomic Studies on Five Species of Sect. Tuberculata (Camellia L.) Based on Morphology, Pollen Morphology and Chloroplast Genomes Evidence

Sect. Tuberculata in the genus Camellia, is named after the tubercle-like projections on the surface of the capsule and ovary. Due to complex morphological variations in these taxon and insufficient field investigations, the interspecific relationships are unclear, the species definitions are vague, and the names are confusing. This is not conducive to the conservation and study of these species. Therefore, herein, we systematically explored the taxonomic status of five sect. Tuberculata species using morphological, pollen morphology, and molecular phylogenetic methods. The result showed that (1) morphological characteristics for the flower, fruit, and leaves of C. anlungensis and C. leyeensis were similar. Furthermore, the pollen characteristics and pollen wall ornamentation showed that it was no significant difference between the two species. (2) there were significant differences between C. acutiperulata and C. anlungensis in terms of leaf shape (elliptic vs. obovate), calyx characteristics (sepal apex pointed vs. sepal oblong), and fruit shape (subglobose folds with shallow verruculose vs. flat folds and verruculose protuberances with pronounced internal cleavage). (3) C. pyxidiacea and C. rubituberculata differed in flower color (white or few light vs. red), fruit verrucae (obviously deeply cleft vs. shallowly uncracked). (4) a phylogenetic tree based on the chloroplast genome showed that C. anlungensis and C. leyeensis form a single clade (BS = 100%, PP = 1.0) and were on a different branch with C. acutiperulata in clade II, (BS = 100%, PP = 1.0); C. pyxidiacea and C. rubituberculata were clustered on different branches of clade I (BS = 99%, PP = 1.00). Integrated above results, we consider that C. leyeensis should be treated as a homonym of C. anlungensis; C. acutiperulata, C. pyxidiacea, C. rubituberculata respectively as a separate species. Clarifying the taxonomic status of these five species not only advances our understanding of the significance and complexity of the systematic classification of the genus Camellia but also has important implications for diversity conservation and population genetics.