Korean orchid taxonomic revision distinguishes Epipactis xanthophaea from E. thunbergii

A taxonomic revision of Korean Epipactis orchids confirms that Epipactis xanthophaea, previously treated as conspecific with Epipactis thunbergii, is a distinct species present in Korea. The study recognizes three species on the Korean Peninsula—E. thunbergii, E. xanthophaea and E. papillosa—and identifies differences in lip structure as the most reliable means of distinguishing the two members of section Arthrochilium.

The researchers combined field observations and measurements of living plants with examinations of original type material, historical herbarium specimens, published descriptions and distribution records. Korean fieldwork on the E. thunbergii-like taxon had begun in 2012 and continued through 2025, while additional investigations in northeastern China were conducted from 2013 to 2019. Type specimens were examined directly or through high-resolution digital images, and voucher material was reviewed from major collections in Korea and elsewhere, including A, AMES, GH, HNWP, IFP, K, KB, KH, KUN, KYO, LE, MHA, MW, PE, P, TI, TNS and WU.

Historically, Korean floras had treated the taxon resembling E. thunbergii as the same species. Its discovery in the northern and southwestern parts of the Baekdudaegan and on western coastal islands prompted a reassessment because earlier floristic accounts did not provide sufficient diagnostic information. Comparison of living material, voucher specimens and type material showed that these Korean plants correspond to E. xanthophaea, a species described from northeastern China in 1922.

The clearest distinction lies in the flower’s lip. E. thunbergii has a short, sometimes inconspicuous mesochile measuring 1–2 mm, a cymbiform hypochile with low ridges and an epichile bearing a pair of low keels. E. xanthophaea instead has an elongated, distinct mesochile measuring 5–6 mm, a smooth cymbiform hypochile without ridges and an ovate-orbicular epichile without keels. The two species share a general resemblance in habit and floral structure, but these consistent lip characters support their separation. By contrast, E. papillosa belongs to section Epipactis and lacks a mesochile; its hypochile is subglobose-saccate and its epichile is narrowly cordate to triangular.

Other measured traits reinforce the identification. E. thunbergii is typically 30–70 cm tall, with lanceolate to ovate-lanceolate leaves, a glabrous inflorescence and dark to light greenish-yellow flowers. E. xanthophaea is generally 40–90 cm tall, with elliptic to ovate-elliptic leaves, a papillose inflorescence and yellowish-brown, yellowish-red or red flowers. The revision reports E. papillosa as 30–80 cm tall, with ovate to broadly ovate leaves, a papillose-pubescent inflorescence and pale green to green flowers.

Habitat records also distinguish the species. E. thunbergii was reported from moist meadows, forest-swamp edges, moist valley edges and coastal rocky areas. E. xanthophaea was associated with sunny, moist sites, including wetlands, marshy ground and the edges of waterways, where its rhizomes may be submerged in deposited silt and water. E. papillosa occurred mainly in shaded deciduous or mixed forests, including sites with calcareous soil, although the revision states that it can tolerate moderately acidic soils.

Herbarium and literature evidence also revised the distribution of E. xanthophaea. Although previously regarded as restricted to northeastern China, it is now recorded from Korea, China and the Russian Far East. Its confirmed Korean distribution includes Jagang-do, Hamgyeongbuk-do, Gangwon-do, Gyeongsangnam-do and Incheon. The Korean populations connect records from northeastern China with those in the Russian Far East, while historical specimens collected in northeastern China and northern Korea support continuity across the region. E. thunbergii is recorded from Korea, Japan and eastern China, and E. papillosa from Korea, northeastern China, the Russian Far East and Japan.

The treatment resolves several nomenclatural questions. Epipactis gigantea var. manshurica is accepted as conspecific with E. xanthophaea rather than E. thunbergii, primarily because of concordant lip morphology, with plant habit, leaf shape and leaf attachment providing additional support. For E. papillosa, the varieties var. imkoeensis and var. sayekiana, as well as E. sayekiana, are treated as synonyms because they do not show consistent morphological differentiation at population level. The study also designates the specimen Limpricht 2915, preserved at WU as WU0061592, as the lectotype of E. xanthophaea because no holotype had been selected in the protologue and the presumed original Berlin material was likely destroyed in 1943.

The conclusions are constrained by the nature of the material available. Some type specimens were assessed from high-resolution digital images rather than direct examination, and the authors explicitly acknowledged the limitations of image-based comparisons. Russian populations were evaluated through herbarium specimens and available digital resources because no direct field investigation was conducted in Russia. In Korea, some reported localities of E. xanthophaea remain unconfirmed: one is supported only by photographs, one by a historical record, and one by a single specimen without recent confirmation. Within these limits, the comparative morphological analysis supports recognizing three Epipactis species on the Korean Peninsula and documents E. xanthophaea as a distinct Korean member of the genus.

Subject of Research: Taxonomic revision and distribution of three Epipactis orchid species on the Korean Peninsula

Article Title: Taxonomic revision of Epipactis Zinn ( Orchidaceae ) on the Korean Peninsula

Article References: Lee, J.-S., Koo, J.-Y., & Kim, M.-H. (2026). Taxonomic revision of Epipactis Zinn (Orchidaceae) on the Korean Peninsula. PhytoKeys, 278, 205-231. https://doi.org/10.3897/phytokeys.278.195337

Image Credits: AI Generated

DOI: 10.3897/phytokeys.278.195337

Keywords: Epipactis, orchids, Orchidaceae, taxonomic revision, Korean Peninsula, plant morphology, species distribution, herbarium specimens, Northeast Asia, Taxonomic, revision, Zinn