The genus Ottelia comprises approximately 21 submerged macrophyte species primarily found in tropical Africa and Southeast Asia. The classification of several Ottelia species as vulnerable under the criteria “A2c” in the China Species Red List emphasizes the urgency of establishing a credible taxonomy. The ambiguity in taxonomy and evolutionary history persists, primarily stemming from the absence of a robust phylogeny at the species level. The rapid progress in high-throughput sequencing technology has facilitated the retrieval of complete chloroplast (cp) genome sequences, offering a molecular foundation for conducting phylogenetic analyses. In this study, the entire cp genomes of five samples of four Ottelia species were sequenced. All five Ottelia samples exhibited a circular, quadripartite-structured molecule, with lengths ranging from 156,823 to 162,442 bp. A total of 75–88 simple sequence repeats (SSRs) in the cp genomes of the five Ottelia samples were observed, which could be used for species identification. A preliminary phylogenetic analysis revealed that O. fengshanensis, O. acuminata, and O. guanyangensis clustered with strong support (100 BS). O. acuminata var. jingxiensis was resolved as a sister to O. acuminata var. lunanensis (100 BS), and both were further found to be sisters to O. balansae. The widely distributed O. alismoides exhibited a close phylogenetic relationship as the sister taxon to all the Chinese endemic taxa, supported by robust values. Together, our thorough examination of the entire cp genomes of the five Ottelia samples provides eminent insights into reconstructing their phylogeny. Furthermore, it illuminates the evolutionary dynamics of the cp genome within the Ottelia genus.

To examine differences in resource use and functional traits between the narrow-ranged Camellia longzhouensis and its widespread congener Camellia gigantocarpa, we compared their light and CO₂ responses, leaf anatomy, stomatal traits, photosynthetic pigments, and trait correlations under common nursery conditions. In both species, net photosynthetic rate increased rapidly with increasing irradiance and then gradually approached a plateau. The maximum net photosynthetic rate of C. gigantocarpa was significantly higher and was 4.10 times that of C. longzhouensis, whereas apparent quantum yield, light saturation point, light compensation point, and dark respiration rate did not differ significantly between the two species. As intercellular CO₂ concentration increased, net photosynthetic rate increased and then gradually leveled off in both species. Initial carboxylation efficiency was significantly higher in C. gigantocarpa, whereas the other CO₂-response parameters showed no significant differences between species. Leaf thickness and lower epidermal thickness were similar between species, but C. gigantocarpa had a thicker upper epidermis and palisade tissue and a higher palisade-to-spongy tissue thickness ratio, whereas C. longzhouensis had thicker spongy tissue and higher stomatal density. Stomatal length, width, and area did not differ significantly between species. C. gigantocarpa had significantly higher chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid contents, as well as a higher chlorophyll a-to-b ratio, whereas the ratio of carotenoids to total chlorophyll did not differ significantly between species. Trait correlations indicated coordinated variation among photosynthetic performance, leaf anatomy, stomatal characteristics, and photosynthetic pigments. Overall, the two species exhibited distinct combinations of leaf structural and photosynthetic functional traits under common nursery conditions, providing baseline ecophysiological information on their resource-use differences and for germplasm conservation of C. longzhouensis.