Chloroplast genomes reveal two new primrose species hidden in China’s karst landscapes

Deep in the limestone landscapes of southwestern China, botanists have identified two primrose species that are entirely new to science. The plants, discovered during field investigations in Sichuan and Guizhou provinces, belong to Primula sect. Auganthus, a group within the primrose family Primulaceae known for rapidly producing new species. Their formal descriptions, published in BMC Plant Biology, rest on a combination of striking field morphology and a detailed comparison of chloroplast genomes, the DNA packages housed in the photosynthetic factories of plant cells.

The two populations immediately caught the attention of the research team, led by Xin Tan and Zhikun Wu of Guizhou University of Traditional Chinese Medicine, together with colleagues from the Kunming Institute of Botany and partner institutions. Both plants bear deeply lobed leaves and distinctly inflated calyces with a flattened base, features that place them squarely within sect. Auganthus. Yet their overall appearance is conspicuously different from every previously described member of the section, a mismatch that raised an urgent question: were these unusual populations merely variants of known species, or did they represent evolutionary lineages that science had never catalogued?

Karst regions, with their dramatic terrain of soluble limestone, sinkholes, and isolated rock outcrops, are famous for strong habitat heterogeneity, meaning that sharply different microhabitats can exist within very small distances. Evolutionary biologists widely consider this patchiness a crucial mechanism underlying species differentiation, particularly for rapidly radiating groups such as the Primulaceae. In such landscapes, populations separated by a cliff face or a dry ridge can experience different light, moisture, and soil chemistry, and over generations these differences can drive divergence. The discovery of two candidate new primroses in these provinces fits this pattern well, and it highlights how much undocumented diversity may still be sheltered in China’s fragmented karst habitats.

To resolve the plants’ identities, the team combined classical morphological analysis with comparative chloroplast genomics. The chloroplast genome, typically around 150,000 base pairs in flowering plants, evolves in a way that makes it ideal for tracing relationships among closely related species. The researchers assembled the chloroplast genomes of the two putative new species alongside those of known sect. Auganthus members and constructed a phylogenetic tree, the branching diagram that shows how lineages are related. In the analysis, the two new species clustered together with all known species of the section, confirming their membership in the group while also revealing their distinct positions within it.

The comparative genomic work went beyond simple tree building. The team performed analyses of boundary contraction and expansion, examining the borders between the large single-copy, small single-copy, and inverted repeat regions of the chloroplast genome, whose shifting boundaries are a well-known source of structural variation. They also carried out a global comparison using mVISTA, a visualization tool that aligns whole genomes to show conserved and variable blocks, and a diversity site analysis to pinpoint regions of high nucleotide diversity among species. These technical approaches together allowed the researchers to see exactly where the genomes of the new species differed from their relatives.

One of the most concrete findings concerns the inverted repeat regions, often abbreviated as IR regions, which are duplicated segments of the chloroplast genome. The IR region lengths of the two putative new species measured 25,403 base pairs and 25,710 base pairs respectively. Differences of this kind in IR length are more than trivia; they reflect structural rearrangements that can help distinguish species and illuminate the evolutionary history of a lineage. Combined with sequence-level differences, such structural data strengthen the case that the two populations are genuinely independent evolutionary units rather than minor variants.

The diversity site analysis detected seven highly variable hotspots across the chloroplast genomes. These hotspots, concentrated in intergenic regions, include the spacers psbI–trnS-GCU, trnS-GCU–trnG-UCC, and trnT-GGU–psbD, as well as the genes accD and ycf1, all of which exhibited high nucleotide diversity among the species examined. Intergenic spacers tend to accumulate mutations faster than coding sequences because they face fewer functional constraints, making them powerful markers for species-level discrimination. The identification of these hotspots is valuable beyond the current study, since such variable regions can serve as DNA barcodes for future surveys of Primula diversity across the region.

Morphology provided the complementary half of the evidence. Each of the two putative new species possesses distinct characteristics that set it apart from its closest relatives, and the paper provides detailed morphological comparisons with closely related species. The plants were named according to their distribution localities: Primula shibingensis, from Shibing, and Primula longmenshanensis, from the Longmen Mountains area. The formal authorship of the names, J.L.Gu & Z.K.Wu, sp. nov., follows the conventions of botanical nomenclature, and the descriptions include information on the distribution ranges and conservation status of both species, an essential step for plants known only from restricted karst localities.

Based on the combined morphological and phylogenetic evidence, the researchers concluded that both newly discovered species are recognized as new to science. The study, published open access on 16 October 2026 and citable under the DOI 10.1186/s12870-026-10039-1, was supported by the National Natural Science Foundation of China and several provincial programs, including the Young Top-notch Talents Program of Yunnan Province and the Guizhou Provincial Science and Technology Project. The work exemplifies how modern genomics can transform a curious field observation into a rigorous species description.

For conservationists, the message is bittersweet. Karst ecosystems in southwestern China are among the planet’s great hotspots of narrow-endemic plants, yet they face pressures from habitat degradation and climate change. Documenting species such as Primula shibingensis and P. longmenshanensis is the first step toward protecting them, because a species that has not been formally described cannot be assessed, listed, or conserved. As chloroplast genome sequencing becomes faster and cheaper, botanists expect more hidden lineages to surface from these ancient limestone terrains, each one a reminder that the inventory of life on Earth is still being written.

Subject of Research: Plant Genetics

Article Title: Comparative chloroplast genomics reveal two new species of Primula sect. Auganthus (Primulaceae) from the karst regions of China: Primula shibingensis and P. longmenshanensis

Article References: Tan, X., Wu, Y., Jiang, X., Gu, J., Jiang, M., Yang, L., Ye, Q., Liu, J., Zhou, W., & Wu, Z. (2026). Comparative chloroplast genomics reveal two new species of Primula sect. Auganthus (Primulaceae) from the karst regions of China: Primula shibingensis and P. longmenshanensis. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10039-1

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10039-1

Keywords: chloroplast genome, Primula, karst, new species, phylogenetics, Primulaceae, China, biodiversity, Comparative, chloroplast, genomics, reveal