Botanists studying a group of wild camellias from southern China have settled a decades-old naming dispute with an unusually thorough package of evidence. A new study published in Botanical Studies on 19 January 2026 concludes that Camellia zengii should be merged into Camellia lipingensis as a heterotypic synonym, while Camellia rhytidocarpa stands as a genuinely distinct species.
The three species belong to section Tuberculata of the genus Camellia, a group of 18 species defined by a distinctive tuberculate-wrinkled fruit pericarp. All three were described by the botanist Hung-Ta Chang in the early 1980s, and a 1993 taxonomic treatment had folded them together into a single species, C. rhytidocarpa, based largely on herbarium specimens with minimal field observation. That merger relied on shared traits such as narrowly lanceolate leaves with caudate or acuminate apices, ovate sepals and ovaries, and sparsely pubescent three-lobed styles. The authors of the new study argue that this approach neglected population-level trait continuity and lacked supporting evidence from molecular phylogenetics, palynology or anatomy.
The type localities of the three taxa are geographically separated. Camellia lipingensis and C. zengii were described from Wulong Mountain in Liping county, Guizhou province, where they grow in mixed forests or bamboo groves, while the type of C. rhytidocarpa comes from Tianping Mountain in Longsheng county, Guangxi, more than 200 kilometers away, where it occupies valley areas in forest understory. When the researchers surveyed these sites in recent years, they found consistent disparities in key floral and fruit traits that convinced them the taxa should not be treated as conspecific, prompting the comprehensive multidisciplinary re-evaluation.
The morphological analysis revealed a nuanced picture. Camellia lipingensis and C. zengii shared brownish mottled bark, red-brown quadrangular branchlets and leathery lanceolate leaves, with overlapping leaf dimensions, petiole lengths, petal sizes, fruit diameters of roughly 2.2 to 3.2 centimeters and consistent subglobose fruit shape. Across the merged taxon, leaves measured 6.42 to 12.50 by 2.16 to 4.45 centimeters, flowers bore 6 to 9 rounded sepals and 3 to 5 hairy styles, filaments ranged from 2.2 to 4.1 centimeters long, and ovaries were 3- to 4-loculed with one seed per locule. Camellia rhytidocarpa, by contrast, differs in leaf serration, leaf shape with occasional oblong leaves and acuminate apices, and a thinner fruit pericarp of 0.30 to 0.49 centimeters.
A principal component analysis of 35 morphological variables separated all samples into three clusters, although the authors note substantial morphological overlap among the taxa, with C. rhytidocarpa displaying the greatest variation. This pattern of continuous variation with discernible differences underscores why the group has been so difficult to classify from specimens alone, and why the team turned to microscopic and genomic characters for corroboration.
Leaf epidermal micromorphology added further discrimination. All three species share irregular epidermal cells with sinuous anticlinal walls on the adaxial surface and anomocytic stomata with reniform guard cells. Crucially, oil glands were absent in C. lipingensis and C. zengii but sparse in C. rhytidocarpa, and the abaxial anticlinal walls were sinuous in the first two versus undulate in the third. Stomatal dimensions overlapped heavily across the group, with elliptical stomata measuring roughly 39.9 to 41.2 by 31.4 to 36.7 micrometers at densities of 62 to 86 per square millimeter, confirming that these anatomical characters are conservative while the gland and wall patterns distinguish C. rhytidocarpa.
Pollen morphology told a similar story. Camellia lipingensis and C. zengii produce nearly identical subspherical pollen with polar axes around 36.7 to 36.8 micrometers, equatorial axes around 40.3 to 41.3 micrometers, P/E ratios of about 0.90, and identical granular exine ornamentation. Camellia rhytidocarpa showed continuous clinal variation with substantial overlap but maintained differences, including a slightly longer polar axis of 37.2 to 37.8 micrometers and a lower P/E ratio, which the authors interpret as pointing to an independent evolutionary path, potentially linked to adaptation to different pollination environments.
The molecular evidence proved decisive. Chloroplast genome assembly showed highly conserved structures: genomes of 157,029 base pairs for C. lipingensis and C. zengii versus 157,048 base pairs for C. rhytidocarpa, identical GC contents of 37.3 percent, and identical gene inventories of 132 genes, comprising 87 protein-coding genes, 37 tRNA genes and 8 rRNA genes. Phylogenetic analyses based on complete chloroplast genomes, protein-coding genes and nuclear ITS sequences all resolved C. lipingensis and C. zengii as a strongly supported monophyletic group, with maximum likelihood bootstrap support of 100 and Bayesian posterior probability of 1.00, while C. rhytidocarpa formed a separate clade sister to it. A selection-pressure analysis of chloroplast protein-coding genes found that two genes, psbA and psaJ, showed Ka/Ks ratios greater than 1, suggesting limited evidence of positive selection in response to environmental pressures.
On the strength of this congruent evidence, the authors formally synonymize Camellia zengii under C. lipingensis, retaining the older name under the principle of priority in botanical nomenclature, and confirm C. rhytidocarpa as a distinct species. The revised C. lipingensis is endemic to Liping county, Guizhou, at elevations of 1,000 to 1,200 meters, while C. rhytidocarpa remains restricted to Tianping Mountain in Longsheng county, Guangxi, within the same altitudinal range. The team suggests that habitat heterogeneity between these regions likely drives the morphological adaptations that distinguish the species, such as leaf serration and pericarp thickness.
Beyond resolving this particular dispute, the study offers a practical framework for untangling morphologically complex plant groups. The authors emphasize that type specimen verification and wild population sampling are essential for species delimitation, noting that digital herbarium records often lack complete floral and fruit characters, a deficiency that has historically led to overreliance on fragmented traits. By integrating field-collected vouchers with microscopic and genomic data, the revision informs conservation prioritization for these narrowly endemic camellias and contributes to standardized species delimitation protocols, with sequences deposited in GenBank under accession numbers including PV761587 and PV750797 through PV750802.
Subject of Research: Taxonomic revision of three Camellia species in section Tuberculata using morphological, anatomical, palynological and molecular evidence
Article Title: Integrative taxonomic revision of three Camellia species from section Tuberculata (Camellia, Theaceae) by morphological, anatomical, palynological, and molecular evidence
Article References: Gu, W., An, M., Yan, C., Xiao, X., Ran, Z., & Li, Z. (2026). Integrative taxonomic revision of three Camellia species from section Tuberculata (Camellia, Theaceae) by morphological, anatomical, palynological, and molecular evidence. Botanical Studies, 67(1), Article 2. https://doi.org/10.1186/s40529-025-00489-5
Image Credits: AI Generated
DOI: 10.1186/s40529-025-00489-5
Keywords: Camellia, taxonomy, section Tuberculata, chloroplast genome, phylogenetics, palynology, leaf epidermis, species delimitation, Theaceae, botany, synonymization, China
News Source: Drew Townsend. (October 29, 2026). Botanists Merge Two Camellia Species and Confirm a Third Using Genomes, Pollen and Fieldwork. Scienmag.
