Abstract
Didymocarpus xuanlienensis, a new species from Vietnam, is described and illustrated here. It is morphologically similar to D. brevipedunculatus and D. purpureobracteatus in terms of corolla size and color but differs from D. brevipedunculatus in leaf blade shape, bract shape, indumentum, and calyx shape and differs from D. purpureobracteatus in peduncle indumentum, bract shape, and calyx shape. A detailed morphological description of the new species and a key to all Didymocarpus species in Vietnam are provided.
Key words: Didymocarpus , new taxon, taxonomy, Vietnam
Introduction
The genus Didymocarpus Wallich (1819: 378) (Gesneriaceae) currently comprises more than 100 species, distributed from India through the Himalayas to southern China, Indochina, and Sumatra (Rhuthuparna and Gowda 2024; Yang et al. 2024; POWO 2026). Historically, however, Didymocarpus included approximately 200 species before Weber and Burtt (1998) redefined the genus and segregated its species into three morphologically distinct genera: Didymocarpus s.s., Henckelia Sprengel, (1817: 402), and the newly established Hovanella Weber & Burtt, (1998: 333). More recently, Liu et al. (2025) reconstructed the molecular phylogeny of Didymocarpus and erected a new genus, Palmatiboea, to accommodate Southeast Chinese species formerly placed in Didymocarpus. In Vietnam, seven species and one variety of Didymocarpus are currently recognized (Tran et al. 2020; Middleton 2023; POWO 2026).
During field surveys in Vietnam on 2 December 2024 and 22 December 2025, an unidentified Didymocarpus species was collected in Xuan Lien National Park, Thuong Xuan Commune, Thanh Hoa Province. Based on comparative morphology, literature review, and examination of relevant herbarium specimens, it was confirmed that it represents a new species, which is described and illustrated below. A key to all known Didymocarpus species in Vietnam is also provided.
Materials and methods
Plant material of the putative new species was collected from Xuan Lien National Park, located in Thuong Xuan Commune, Thanh Hoa Province, Vietnam. Type specimens have been deposited in the herbarium of the Vietnamese Academy of Forest Sciences (VAFS). Taxonomic descriptions are based on measurements taken from both fresh and dried specimens. Field surveys were carried out in the type locality and surrounding areas, and the conservation status was assessed following the IUCN Red List Categories and Criteria (IUCN Standards and Petitions Committee 2024).
Taxonomic treatment
Didymocarpus xuanlienensis
T.S.Hoang, W.G.Wang & H.C.Xi sp. nov.
96DC8AFF-7008-5FBE-9E6E-7AD45227D514
urn:lsid:ipni.org:names:77380512-1
Figure 1.
Didymocarpus xuanlienensis T.S.Hoang, W.G.Wang & H.C.Xi, sp. nov. A. Habitat; B. Flowering plant; C. Leaves, adaxial and abaxial views; D. Inflorescences; E. Part of inflorescence, showing peduncle, pedicel and bracts; F. Bracts; G. Calyx and disc; H. Flowers; I. Dissected corolla, showing stamens and pistil (Photos by Son Thanh Hoang).
Type.
Vietnam • Thanh Hoa Province, Thuong Xuan Commune, Xuan Lien Nature Reserve, in evergreen forest on wet rocks, 574 m a.s.l., 20°01'N, 105°02'E, 22 December 2025, Son Thanh Hoang, XL5316 (holotype: VAFS; isotype: VAFS).
Diagnosis.
The new species differs from the most similar species, Didymocarpus brevipedunculatus Y.H.Tan & Bin Yang, (2019: 191), in leaf blade elliptic to oblong, base cuneate (vs. ovate, base extremely obliquely cordate); bracts broadly ovate, glabrous (vs. orbicular to ovate, sparsely villous); calyx broadly campanulate, lobes triangular (vs. campanulate, lobes ovate to semiorbicular). D. xuanlienensis is also similar to D. purpureobracteatus W.W.Smith, (1912: 153) but differs from it in peduncle glandular-pubescent (vs. glabrous); bracts free (vs. often connate at base); calyx actinomorphic, broadly campanulate, lobes triangular (vs. slightly zygomorphic, tubular campanulate, lobes semiorbicular). Moreover, the new species differs from D. brevipedunculatus and D. purpureobracteatus in distribution, elevation, and flowering time. A detailed morphological and ecological comparison of these three species is presented in Table 1.
Table 1.
Morphological and ecological comparison of Didymocarpus xuanlienensis, D. brevipedunculatus, and D. purpureobracteatus.
| Characters | D. xuanlienensis | D. brevipedunculatus | D. purpureobracteatus |
|---|---|---|---|
| Petiole | 1.1–1.7 cm long | 4.5–12.0 cm long | 0.3–11.0 cm long |
| Leaf blade shape | Elliptic to oblong, base cuneate, apex acuminate | Ovate, base extremely obliquely cordate, apex attenuate to acuminate | Ovate to elliptic or obovate, base cuneate to cordate, apex acute to acuminate |
| Leaf blade indumentum | Adaxially and abaxially appressed pubescent | Adaxially densely villous with eglandular, multicellular hairs, abaxially densely villous with eglandular, multicellular hairs along veins | Adaxially sparsely appressed puberulent to glabrous, abaxially puberulent to nearly glabrous along veins |
| Peduncle | Glandular-pubescent | Densely villous with eglandular, multicellular hairs | Glabrous |
| Bract | Green, broadly ovate, glabrous | Green to light green, orbicular to ovate, sparsely villous with eglandular, multicellular hairs | Purple, often connate at base, ovate to elliptic-ovate, glabrous |
| Calyx | Red to light green outside, actinomorphic, broadly campanulate, ca. 5 mm long; lobes triangular | Often light green, sometimes purplish outside, campanulate, 6–7 mm long; lobes ovate to semiorbicular | Purple, slightly zygomorphic, tubular campanulate, 10–12 mm long; lobes semiorbicular |
| Corolla | 3.3–3.9 cm long, white, with 15 longitudinal pink striations | 4.0–4.5 cm long, white, inside with nine purplish to deep red longitudinal stripes | 3.2–4.5 cm long, purple to pinkish purple with darker stripes |
| Distribution and habitat | Thanh Hoa, Vietnam, ca. 574 m a.s.l. | Yunnan, China, ca. 1200 m a.s.l. | Yunnan, China, 1400–2200 m a.s.l. |
| Phenology | Flowering October–December | Flowering August–September | Flowering August–September |
Description.
Herbs perennial, lithophytic, up to 50 cm tall. Stems erect, appressed pubescent. Leaves opposite; petiole 1.1–1.7 cm long, appressed pubescent; blade herbaceous, elliptic to oblong, 12.5–19.5 × 5.5–7 cm, base cuneate, often oblique, apex acuminate, margin serrate to subentire, adaxially dark green, appressed pubescent, abaxially light green, appressed pubescent; venation pinnate, lateral veins 7–9 pairs. Inflorescences terminal or subterminal, cymose, 7–15-flowered; peduncles 3.5–6 cm long, glandular-pubescent; bracts paired, green, broadly ovate, 3–5 mm long, 4–6.5 mm wide, glabrous on both surfaces. Pedicel 4–18 mm long, glandular-pubescent. Calyx actinomorphic, broadly campanulate, ca. 5 mm long, shallowly 5-lobed, outside red to light green, glabrous, inside light green; lobes bent outward, equal, triangular, ca. 1.5 mm long, 2.5 mm wide. Corolla 3.3–3.9 cm long, white, with 15 longitudinal pink striations extending from corolla tube to lobes, glabrous on both surfaces; tube infundibuliform-tubular, 2.1–2.6 cm long; upper lip 2-lobed, lobes round, ca. 4 mm long, 6 mm wide; lower lip 3-lobed, lobes subround, lateral lobes ca. 5 mm long, 6 mm wide, central lobe ca. 5 mm long, 6.5 mm wide. Stamens 2, adnate to ca. 1.5 cm above the corolla base; filaments ca. 1 cm long, glabrous; anthers coherent, ca. 3 mm long, pale yellow, villous. Staminodes 3, linear, lateral staminodes 2–4 mm long, central staminode ca. 3 mm long, adnate to 1.5–2 cm above the corolla base. Disc cupular, ca. 2 mm high. Pistil 2.2–2.5 cm long; ovary linear, 1.8–2.1 cm long, glabrous; style 2–3 mm long, sparsely pubescent to subglabrous; stigma capitate. Capsules not seen.
Etymology.
The specific epithet “xuanlienensis” refers to the type locality in Xuan Lien National Park, Vietnam. A Vietnamese name is proposed here as “Song quả Xuân Liên”.
Phenology.
Flowering from October to December.
Distribution and habitat.
Currently, this species is known only from the type locality, where it grows on moist rocks within an evergreen forest at an elevation of ca. 574 m.
Conservation assessment.
Only a single population with fewer than 20 mature individuals of Didymocarpus xuanlienensis has been recorded to date. The extent of occurrence (EOO) is less than 100 km2, and the area of occupancy (AOO) is less than 10 km2. However, this population and its habitat are well protected within Xuan Lien National Park, with no signs of human disturbance, and are not expected to be subject to any human interference or destruction in the foreseeable future. Consequently, following the IUCN Red List Categories and Criteria (IUCN Standards and Petitions Committee 2024), its threat status is currently assessed as “Critically Endangered” (CR) (B1B2aD).
Key to the species of Didymocarpus in Vietnam
| 1 | Ovary glabrous | 2 |
| – | Ovary pubescent | 5 |
| 2 | Leaf blade near round or broadly elliptic | D. kerrii |
| – | Leaf blade ovate, elliptic, or oblong | 3 |
| 3 | Corolla pubescent outside | D. punduanus var. pulcher |
| – | Corolla glabrous on both surfaces | 4 |
| 4 | Leaf blade apex acute; bract rounded, connate at base; corolla 2.6–3.4 cm long, red | D. tamdaoensis |
| – | Leaf blade apex acuminate; bract broadly ovate, free; corolla 3.3–3.9 cm long, white with pink striations | D. xuanlienensis |
| 5 | Bract lanceolate or oblong-lanceolate | 6 |
| – | Bract ovate, elliptic ovate, or orbicular | 7 |
| 6 | Base of leaf often axisymmetric; bract 2–3 mm long | D. poilanei |
| – | Base of leaf asymmetric; bract 4–5 mm long | D. phuquocensis |
| 7 | Bract less than 3 mm long; corolla white, less than 3 cm long | D. dalatensis |
| – | Bract more than 3 mm long; corolla pinkish-purple to blackish-purple, more than 3 cm long | 8 |
| 8 | Peduncle glabrous; bracts connate at base; calyx 1–1.2 cm long; corolla purple to pinkish-purple with darker stripes | D. purpureobracteatus |
| – | Peduncle glandular hairy; bracts separate; calyx 6 mm long; corolla blackish-purple | D. puhoatensis |
Discussion
The karst area in southern China and northern Vietnam is well known for its high levels of biodiversity and endemism (Zhu 2007). The discovery of Didymocarpus xuanlienensis in northern Vietnam highlights the Indochina-China transition zone as a critical hotspot for Gesneriaceae diversity (Wang et al. 1998; Tan et al. 2020, 2025; Wei et al. 2022). This finding aligns with recent studies that reveal congruent spatial patterns of species richness and phylogenetic diversity in karst flora (Xu et al. 2021). The high levels of diversity and endemism within Didymocarpus likely stem from an explosive radiation of gesneriad lineages during the Miocene, a process that was further shaped by paleoclimatic fluctuations in southern China and Indochina, which acted as major drivers of speciation in these specialized karst habitats (Kong et al. 2022; Tan et al. 2026).
The new species grows on moist rocks within karst evergreen forests, exhibiting the specialized lithophytic habit common among many Gesneriaceae species (Wang et al. 1998; Tan et al. 2020). Unfortunately, karst landscapes worldwide are facing increasing threats from both climate change and human activities (Clements et al. 2006). Known from only a single population, this new taxon underscores the need for continued field surveys in under-explored national parks. In addition, integrating this new record into comprehensive regional checklists is essential for maintaining accurate knowledge of the geographical distribution of Gesneriaceae across the Asian tropics.
Supplementary Material
Citation
Tran VTT, Hoang ST, Wang W-G, Lang X-A, Xi H-C (2026) Didymocarpus xuanlienensis, a new species of Didymocarpus (Gesneriaceae) from Vietnam. PhytoKeys 275: 73–79. https://doi.org/10.3897/phytokeys.275.185766
Funding Statement
Vietnam Academy of Science and Technology: project code VAST05.03/25-26
Contributor Information
Xiao-An Lang, Email: langxa@126.com.
Hou-Cheng Xi, Email: xihoucheng@xtbg.ac.cn.
Additional information
Conflict of interest
The authors declare that there is no conflict of interest in conducting this study.
Ethical statement
No ethical statement was reported.
Artificial Intelligence (AI) use
The authors accept full responsibility for the content of the manuscript, including the disclosure of any use of AI.
No AI tools were used in the preparation of this manuscript.
Funding
This study was carried out with funding from project code VAST05.03/25-26. The authors would like to express their sincere gratitude for this valuable support.
Author contributions
Conceptualization: WGW, HCX. Data curation: VTTT. Investigation: STTH, VTTT. Methodology: XAL. Resources: WGW, STTH. Supervision: HCX, XAL. Validation: HCX. Writing – original draft: VTTT. Writing – review and editing: XAL, HCX.
Author ORCIDs
V.T.T. Tran https://orcid.org/0009-0005-1065-9639
S.T. Hoang https://orcid.org/0000-0003-0351-929X
W.-G. Wang https://orcid.org/0000-0002-7372-147X
X.-A. Lang https://orcid.org/0000-0001-5362-9580
Data availability
All of the data that support the findings of this study are available in the main text.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
All of the data that support the findings of this study are available in the main text.