Background: Section Camellia is the most diverse group in the genus Camellia L., and this group of plants has a long history of cultivation in China as popular ornamental flowers and oil plants. Sect. Camellia plants present diverse morphological variations and complexity among species, resulting in uncertainty in the classification of species, which has resulted in a degree of inconvenience and confusion in the use of plant resources and research. Methods: Here, We sequenced and assembled the chloroplast genomes of 6 sect. Camellia and performed comparative chloroplast genome analysis and phylogenetic studies combined with 15 existing sect. Camellia plants. Results: The chloroplast genome of 21 species in sect. Camellia species were quadripartite with length of 156,587–157,068 bp base pairs (bp), and a highly conserved and moderately differentiated chloroplast genome arrangement. The 21 sect. Camellia chloroplast genomes were similar to those of angiosperms, with high consistency in gene number, gene content and gene structure. After the annotation process, we identified a total of 132 genes, specifically 87 sequences coding for proteins (CDS), 37 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. The ycf1 gene in 21 species of the sect. Camellia was present only in the small single-copy/inverted repeat of a (SSC/IRa) region. Sequence variation was greater in the large single-copy (LSC) region than in the IR region, and the majority of the protein-coding genes presented high codon preferences. The chloroplast genomes of 21 plant species exhibit relatively conserved SC (single copy region)/IR (inverted repeat region) boundaries. We detected a total of 2975 single sequence repeats (SSRs) as well as 833 dispersed nuclear elements (INEs). Among these SSRs, A/T repeats and AT/AT repeats dominated, while among INEs, forward repeats and palindromic repeats predominated. Codon usage frequencies were largely similar, with 30 high-frequency codons detected. Comparative analysis revealed five hotspot regions (rps16, psaJ, rpl33, rps8, and rpl16) and two gene intervals (atpH-atpI and petD-rpoA) in the cp genome, which can be used as potential molecular markers. In addition, the phylogenetic tree constructed from the chloroplast genome revealed that these 21 species and Camellia oleifera aggregated into a single branch, which was further subdivided into two evolutionarily independent sub-branches. Conclusions: It was confirmed that sect. Camellia and C. oleifera Abel are closely related in Camellia genus. These findings will enhance our knowledge of the sect. Camellia of plants, deepen our understanding of their genetic characteristics and phylogenetic pathways, and provide strong support for the scientific development and rational utilization of the plant resources of the sect. Camellia.

Sect. Tuberculata Chang in the genus Camellia (Theaceae Mirb.) 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 interspecies 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 explore the taxonomic status of five sect. Tuberculata species using morphological, pollen morphological, and molecular phylogenetic methods. The results showed that (1) the morphological characteristics of the flower, fruit, and leaves of C. anlungensis and C. leyeensis are similar. Furthermore, the pollen characteristics and pollen wall ornamentation show that there is no significant difference between the two species; (2) there are 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 differ in flower color (white or light color vs. red) and fruit verrucae (obviously deeply cleft vs. shallowly uncracked); (4) a phylogenetic tree based on the chloroplast genome shows that C. anlungensis and C. leyeensis form a single clade (BS = 100%, PP = 1.0) and are on a different branch, with C. acutiperulata on clade II (BS = 100%, PP = 1.0), and C. pyxidiacea and C. rubituberculata clustered on different branches of clade I (BS = 99%, PP = 1.00). Considering the above results together, we propose that C. leyeensis should be treated as a homonym of C. anlungensis, and C. acutiperulata, C. pyxidiacea, and C. rubituberculata should be considered as 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.

Sect. Tuberculate Chang belongs to the genus Camellia, which is an endemic group in China and has high research value. However, the phenotypic patterns of this taxon are complex and diverse, and the phenotypic variation in key traits is still unclear. In this study, a total of 212 samples from 18 populations of sect. Tuberculate plants were studied for 30 phenotypic traits of flowers, fruits, and leaves using analysis of variance, correlation analysis, principal component analysis, and cluster analysis. The results showed the following. (1) The plants in sect. Tuberculate were rich in phenotypic trait variation and possessed rich phenotypic diversity. The differentiation of phenotypic traits mainly came from among populations, with leaves (66.804%) being the largest and flowers (53.476%) being the smallest. Qualitative traits (70.264%) were greater than quantitative traits (57.608%). (2) Correlation analyses showed close and complex relationships among the phenotypic traits of flowers, fruits, and leaves. (3) The cumulative contribution of the first 10 principal components was up to 73.49%, which screened out 12 major traits contributing to the phenotypic differences in plants of sect. Tuberculate. (4) Q-type analysis showed that they were classified into 18 taxa at a Euclidean distance of 7.5 and 11 taxa at a Euclidean distance of 10. The 18 populations were not fully clustered according to the geographic distance of the plants, and there was an overlap between some of the populations. In summary, the degree of variation in phenotypic traits among populations of sect. Tuberculate plants is high, which is affected by the climatic environment. The 12 major phenotypic traits screened can be used as the basis for the classification of sect. Tuberculate plants. There are trait overlaps among some populations, which may be affected by the stochastic influence of the geographic climate and gene flow. This study will provide important references for interspecific identification, classification system construction, genetic mechanism, germplasm resource conservation, and exploitation of plants in sect. Tuberculate.

Changes in habitat suitability are critical indicators of the ecological impacts of climate change. Syndiclis Hook. f., a rare and endangered genus endemic to montane limestone and cloud forest ecosystems in China, holds considerable ecological and economic value. However, knowledge of its current distribution and the key environmental factors influencing its habitat suitability remains limited. In this study, we employed the MaxEnt model, integrated with geographic information systems (ArcGIS), to predict the potential distribution of Syndiclis under current and future climate scenarios, identify dominant bioclimatic drivers, and assess temporal and spatial shifts in habitat patterns. We also analyzed spatial displacement of habitat centroids to explore potential migration pathways. The model demonstrated excellent performance (AUC = 0.988), with current suitable habitats primarily located in Hainan, Taiwan, Southeastern Yunnan, and along the Yunnan–Guangxi border. Temperature seasonality (bio7) emerged as the most important predictor (67.00%), followed by precipitation of the driest quarter (bio17, 14.90%), while soil factors played a relatively minor role. Under future climate projections, Hainan and Taiwan are expected to serve as stable climatic refugia, whereas the overall suitable habitat area is projected to decline significantly. Combined with topographic constraints, population decline, and limited dispersal ability, these changes elevate the risk of extinction for Syndiclis in the wild. Landscape pattern analysis revealed increased habitat fragmentation under warming conditions, with only 4.08% of suitable areas currently under effective protection. We recommend prioritizing conservation efforts in regions with habitat contraction (e.g., Guangxi and Yunnan) and stable refugia (e.g., Hainan and Taiwan). Conservation strategies should integrate targeted in situ and ex situ actions, guided by dominant environmental variables and projected migration routes, to ensure the long-term persistence of Syndiclis populations and support evidence-based conservation planning.

To clarify the soil nutrient status and identify the safety risks of heavy metals in Camellia oleifera planting regions, the integrated soil fertility status was assessed using the improved Nemero composite index method, weighted average method, and coefficient of variation (CV) method, and the impact of heavy metals in the soil on human health was evaluated with a health risk assessment model using the Qianyu C. oleifera planting base in Yuping County, Guizhou Province, as the study object. The results showed the following: (1) The soil pH levels were 4.12–6.17, with CV values of 0.04–0.66, and no significant differences were observed among the plots. The soil was rich in organic matter, alkali-hydrolyzed nitrogen, and available phosphorus, with a high total potassium content, total phosphorus content, and rapidly available potassium, indicating a high level of comprehensive soil fertility. (2) The total carcinogenic risk (CR) index of the arsenic (As), cadmium (Cd), and chromium (Cr) in the soil was 1.92 × 10⁻⁷, and among these elements, the CR index of the As was the highest (1.3–8.0 × 10⁻⁷), but all were below the highest acceptable level (10⁻⁶) recommended by the United States Environmental Protection Agency (USEPA). (3) The redundancy analysis (RDA) between the soil fertility and trace elements revealed that the soil organic matter content was positively correlated with the contents of lead (Pb), manganese (Mn), and Cr and negatively correlated with the contents of zinc (Zn), iron (Fe), Cd, mercury (Hg), As, and copper (Cu). The soil pH was positively correlated with the contents of Cr, Fe, and Cu and negatively correlated with the contents of Mn, Pb, Zn, Cd, Hg, and As. In the study area, the soil was slightly acidic with overall high fertility without any CR. The quality of the C. oleifera was degraded by soil acidification, but the slightly acidic soil facilitated the absorption of trace elements by C. oleifera. Soil acidification could be relieved by taking appropriate measures, such as the addition of biochar or CaCO₃. This study determined the soil fertility of the Qianyu C. oleifera planting base and assessed the health risk of heavy metals in the soil, providing a theoretical reference for enhancing C. oleifera quality, preventing the excessive accumulation of soil heavy metals, and improving the soil in this planting base.

Geodorum eulophioides is a unique and endangered species belonging to the Orchidaceae family in China. It has great potential as an ornamental horticultural plant. However, little is known about its genetic diversity and reasons for being endangered due to its narrow distribution and few populations in the wild. To effectively evaluate and conserve available resources, the genetic diversity and population structure of G. eulophioides were analyzed in this study. A total of 94 individuals from 10 natural populations were studied using site-specific amplified fragment sequencing (SLAF-seq). Based on the 76,340 SNPs detected by SLAF-seq, genetic diversity analysis was performed and markers associated with environmental variables were determined. The results showed that the level of genetic diversity in the 10 natural populations studied was low, with PIC values ranging from 0.1874 to 0.2156. FIS values ranged from −0.2376 to 0.2658, with excess and deficiency in heterozygotes. FST values ranged from 0.0482 to 0.3144, with genetic variation among populations. AMOVA results showed that the genetic variation among populations accounted for 21.35% of the total variation, and the remaining genetic variation among individuals within populations was 78.65%. The results of the population structure analysis showed that 94 individuals were classified into three major groups and two subgroups. Environmental association analysis using Bayenv2 and LFMM yielded thirty and eighteen putative adaptive loci, respectively, and five specific functional genes were annotated. In summary, this study provides further insight into the genetic structure of G. eulophioides and provides a reference for protection and restoration.