During February 2024 and July 2025, four field surveys were carried out at the type locality of the new species. Specimens from several herbaria were examined, including GYBG, GZTM, HGAS, HIB, IBK, IBSC, KUN, NAS, and PE (herbarium abbreviations follow the conventions outlined by Thiers (2025)). Additionally, we consulted several online databases, including the China Plant Photography Database (http://ppbc.iplant.cn/), the Chinese Field Herbarium (http://www.cfh.ac.cn/), and Global Plants (http://plants.jstor.org/), to obtain supplementary information on species distributions and morphological data. To distinguish the new species from other species of Paraphlomis, we conducted detailed morphological comparisons, focusing on key characteristics such as stems, leaves, calyx, corolla, mericarps, and trichomes. All measurements were made using a dissecting microscope. The morphological description followed relevant taxonomic and floristic literature on Paraphlomis, with terminology standardized according to Li and Hedge (1994b), ensuring consistent and accurate morphological interpretation.

For the molecular phylogenetic reconstruction of Paraphlomis, we included a total of 53 samples: 38 representing Paraphlomis taxa (34 species and four varieties) and two outgroup taxa. The outgroups comprised Phlomoides dentosa var. glabrescens (Danguy) C.L. Xiang & H. Peng and Phlomis fruticosa L. Only one accession of the new species was sampled and sequenced in this study, while sequence data for other species were obtained from GenBank and previous studies (Chen et al. 2021, 2022a, 2022b).

Genomic DNA was extracted from dried leaf tissue using a modified CTAB method (Doyle and Doyle 1987). Previous studies have shown that phylogenetic trees based on nuclear ribosomal DNA internal and external transcribed spacers (nrITS and nrETS) offer more effective insights into the phylogenetic relationships of Paraphlomis than those constructed using chloroplast DNA (Chen et al. 2021; Yuan et al. 2024). Thus, only the nrDNA data was used here for phylogenetic reconstruction. Voucher information and GenBank accession numbers for all sequences are provided in Appendix 1.

The best-fitting substitution model was selected using the Akaike Information Criterion (AIC) based on sequence data in jModelTest v.2.1.7 (Darriba et al. 2012). Phylogenetic analyses were performed using Bayesian Inference (BI) and Maximum Likelihood (ML) methods, employing MrBayes (Ronquist et al. 2012) and RAxML v.8.2.9 (Stamatakis 2014) on the CIPRES Science Gateway v.3.3 (Miller et al. 2010), respectively. The Markov chain Monte Carlo algorithm was run for 20 million generations with four incrementally heated chains starting from random trees and sampling one out of every 1,000 generations. The initial 25% of sampled trees were discarded as burn-in and the 50% majority-rule consensus tree was calculated from remaining trees with nodal support summarized as posterior probabilities (PP). All phylogenetic trees were visualized and edited for clarity using FigTree v.1.4.2 (Rambaut 2014), with PP and bootstrap support (BS) values annotated on the branches.

Morphological comparisons were based on an examination of 196 specimens representing 14 species of Paraphlomis. A key diagnostic character of the potential new species P. leigongshanensis is the hairy mericarps, which serves as an important taxonomic feature for the infrageneric classification (Chen et al. 2021; Yuan et al. 2024). Morphologically, P. leigongshanensis is most similar to P. jiangyongensis in the dwarf habit ascending stems, and hairy mericarps (Table 1). However, it differs from P. jiangyongensis by its abaxially purple (vs. green) laminae, calyx teeth acuminate (vs. acute) at apex, and longer corolla tubes. Additionally, the corolla of P. leigongshanensis is white with pink stripes and spots, with the markings concentrated on the lower lip, differing from the pale yellow corolla lips with red spots in P. jiangyongensis. This species is distributed in the mid-subtropical evergreen broad-leaved forests in Leishan County, Guizhou, exhibiting geographical isolation from P. jiangyongensis (Appendix 2: Fig. A1).

The concatenated nrDNA dataset had a total length of 1259 bp, comprising 814 bp from the ITS region and 445 bp from the ETS region. The dataset contained 356 variable sites (168 from ITS, 188 from ETS) and 205 parsimony-informative characters (89 from ITS, 116 from ETS).

The resulting phylogenetic tree of Paraphlomis was consistent with previous studies (Chen et al. 2021; Yuan et al. 2024). The potential new species P. leigongshanensis was resolved as sister to P. gracilis var. lutienensis (Y. Z. Sun) C. Y. Wu (Fig. 1: BS = 100%/PP = 1.00), and the P. leigongshanensis–P. gracilis var. lutienensis clade was further sister to P. gracilis var. gracilis Kudô (Fig. 1: BS = 100% / PP = 1.00). The three taxa were all nested within the “Clade III” proposed by Chen et al. (2021) and Yuan et al. (2024) (Fig. 1: BS = 83%/PP = 1.00). Species in this clade (highlighted in blue in Fig. 1) are all characterized by hairy mericarps (Chen et al. 2021; Yuan et al. 2024). Despite the close relationships and geographical affinities (Appendix 2: Fig. A1) among P. leigongshanensis, P. gracilis var. gracilis, and P. gracilis var. lutienensis, P. leigongshanensis is morphologically distinct from the latter two taxa. Specifically, P. leigongshanensis exhibits a creeping habit with stems 5–10 cm tall, ovate to elliptic leaves, reddish-purple calyces, sessile flowers, and white corollas with pink stripes and spots. In contrast, P. gracilis var. gracilis has erect and much taller stems (up to 1 m tall), lanceolate leaves, green calyces, subsessile flowers, and yellowish green to white corollas with purple spots (Table 1). Paraphlomis gracilis var. lutienensis differs from both species by its subsessile and narrowly lanceolate laminae and yellow corollas. Moreover, a recent phylogenetic study based on plastome data (Yuan et al. 2024) indicated that the phylogenetic relationship between P. gracilis var. gracilis and P. gracilis var. lutienensis is consistent with the results of our study. Based on our phylogenetic results, although P. leigongshanensis is grouped with P. gracilis var. gracilis and P. gracilis var. lutienensis, there is sufficient evidence to support its recognition as a distinct species. The morphological differences further reinforce its taxonomic distinctiveness and provide additional support for its designation as a new species.