Lysimachia L. (Linnaeus 1753: 146) is a morphologically diverse genus, representing the second-largest group within the subfamily Myrsinoideae of Primulaceae (Angiosperm Phylogeny Group 2016). It comprises approximately 250 species globally, primarily distributed across temperate and subtropical regions of the Northern Hemisphere (Hu and Kelso 1996), with particularly high diversity observed in the tropical Karst landform areas of Asia (Yan et al. 2018, 2025). The monophyly of Lysimachia s.s. has been challenged by both morphological and molecular data. Subsequent phylogenetic analyses confirmed this by demonstrating that several satellite genera (namely Anagallis L., Asterolinon Hoffmanns. & Link, Glaux L., Pelletiera A.St.-Hil., and Trientalis L.) are deeply embedded within Lysimachia, thereby establishing a more robust phylogenetic framework for the genus (Anderberg and Ståhl 1995; Hao et al. 2004; Anderberg et al. 2007; Liu et al. 2023; Dong et al. 2025).

China represents a major centre of Lysimachia diversity, encompassing 138 to 150 species (Chen et al. 1989; Hu and Kelso 1996), with the highest concentrations found in its southern and southwestern regions. Due to this complexity and high endemism, recent systematic efforts continue to result in the discovery and formal description of numerous new species (e.g. Huang et al. 2020; Mou et al. 2020; Ke et al. 2021; Lu et al. 2021; Zhang et al. 2024; Quan et al. 2025; Xiong et al. 2025; Xu et al. 2025).

The Lysimachia flora of southwestern China exhibits strong biogeographical affinities with that of Southeast Asia, including Myanmar, Thailand, Laos, Vietnam, and the Malay Peninsula. During recent botanical expeditions in southern Yunnan (2021–2022), we rediscovered L. peduncularis Wall. ex Kurz, representing its first record in China in nearly half a century. This prolonged hiatus has not only hindered conservation assessments but also obscured the species’ taxonomic identity and phylogenetic position. Furthermore, existing descriptions in Flora Reipublicae Popularis Sinicae and Flora of China remain rudimentary, providing insufficient morphological detail for robust species delimitation or systematic comparison. Consequently, a comprehensive re-evaluation of this elusive species is urgently required.

The nuclear ribosomal DNA (nrITS) sequence of L. peduncularis was determined to be 627 bp in length (GenBank accession number: PQ451564). The assembled complete plastid genome (plastome) of L. peduncularis (GenBank accession number: PV299159) spanned 155,376 bp in length and exhibited a typical quadripartite (QP) structure (Fig. 1). This structure consists of a large single-copy (LSC) region of 70,374 bp, a small single-copy (SSC) region of 17,648 bp, and two inverted repeats (IRs) of 26,361 bp each.

The systematic position of L. peduncularis was evaluated using three datasets: nrITS, combined plastid loci, and the complete plastome. All three datasets consistently resolved L. peduncularis as firmly nested within L. subg. Idiophyton (Fig. 2). Specifically, the species consistently formed a strongly supported clade as the sister species to the lineage comprising L. laxa and L. lancifolia Craib (Suppl. material 3). The statistical support for this sister relationship remained high across all datasets. The nrITS phylogeny provided strong support (BS = 99; PP = 1.00); the combined three plastid loci phylogeny also showed high support (BS = 89; PP = 0.99); and the complete plastome phylogeny yielded the highest support (BS = 100) (Fig. 2). The phylogenetic analyses thus confirm the systematic position of the species and provide a robust molecular framework for the subsequent re-evaluation of its morphology.

Based on the confirmed systematic position through molecular data, and the critical comparison with type specimens, the rediscovery of L. peduncularis in China is formally confirmed and a detailed supplementary description is provided.

The collection Wallich Cat. 1489 comprises material from two localities: Ava, Taong Dong and Prome Hills, both collected in 1826. These specimens represent syntypes of L. peduncularis, as Kurz validated the name without designating a holotype. Bennell and Hu (1983) conducted a detailed morphological and palynological comparison and confirmed that the material from both localities unquestionably belongs to the same species. No formal lectotypification has been published to date.

When verifying the identity of newly collected Lysimachia material, we were confronted with the question of which duplicate best serves as the nomenclatural type of L. peduncularis, even though all syntypes are taxonomically conspecific. Following the implicit reference in Hu (1985) to the Taong Dong gathering and in accordance with Art. 9.3, 9.11, and 9.12 of the International Code of Nomenclature for algae, fungi, and plants (Madrid Code) (Turland et al. 2025), we here designate as lectotype the best-preserved and most complete specimen from Taong Dong housed at K (Wallich Cat. 1489, K000750700), which fully matches the protologue and exhibits all diagnostic characters.

The most recent confirmed collection of L. peduncularis in China dates back to 1973 (孟连调查队 10213, HITBC 042682), marking a nearly half-century hiatus in regional records. This study formally reports the rediscovery of L. peduncularis in southern Yunnan, to the north of the former record, a finding crucial for confirming the species’ current status and expanding its known distribution. Prior molecular studies on L. peduncularis relied solely on an accession from Thailand (Larsen et al. 44904, AAU; Fig. 7) (Anderberg et al. 2007). By including newly collected Chinese specimens, comparing them morphologically and molecularly with Thai material, and, crucially, presenting the first complete plastid genome of the species, our work provides a robust and long-overdue update to its taxonomy and systematics (Fig. 2; Suppl. material 3).

Traditionally, L. peduncularis was placed within L. subg. Lysimachia sect. Alternifoliae because its filaments significantly exceed the anthers in length (Handel-Mazzetti 1928; Chen and Hu 1979; Bennell and Hu 1983). This elongated filament character was recognized as a key evolutionary polarity in the Chinese Lysimachia flora (Chen and Hu 1979). Such morphological evidence appeared to justify the species’ previous systematic status by aligning macroscopic observations with traditional taxonomic views (Bennell and Hu 1983).

However, our molecular phylogenetic analyses robustly place L. peduncularis within L. subg. Idiophyton. This result reaffirms earlier studies based on a limited number of markers (Anderberg et al. 2007; Yan et al. 2018) and confirms that its former classification under L. subg. Lysimachia was incorrect. The strong support across all phylogenies for L. peduncularis as sister to the L. laxa and L. lancifolia clade reinforces this conclusion. Furthermore, our results confirm the monophyly of L. subg. Idiophyton and highlight the paraphyly of L. subg. Lysimachia, which is consistent with recent findings (Liu et al. 2023). This phylogenetic framework underscores the necessity of a formal taxonomic revision to transfer L. peduncularis to L. subg. Idiophyton.

In light of this molecular placement, our documentation of seed morphology provides critical supplementary evidence. According to the character types defined by Oh et al. (2008), the small, obliquely sectoroid to polyhedral seeds of L. peduncularis, which measure approximately 0.7 mm in diameter, align with the predominant forms observed in the genus. Crucially, the tuberculate surface ornamentation serves as a significant diagnostic feature that distinguishes this species from many members of L. subg. Lysimachia, which typically possess winged or smooth seeds. This micromorphological consistency supports our phylogenomic results and indicates that despite its misleading floral morphology, the reproductive characters, particularly seed shape and seed coat texture, retain conservative characters congruent with its placement in L. subg. Idiophyton.

Beyond these taxonomic implications, the rediscovery of L. peduncularis after a nearly half-century absence of botanical records underscores its extreme rarity within China. The biogeographical continuity between southern Yunnan and adjacent Southeast Asian regions suggests that effective conservation should adopt a transboundary perspective to fully comprehend the population dynamics and long-term viability of the species across its entire range. Accordingly, the limited size of the confirmed population necessitates immediate attention through a formal IUCN Red List assessment and the swift implementation of targeted protection measures in China.