This species is most similar to Calanthe sieboldii in habit, gross morphology and flower colour, but differs from the latter in having smaller flowers (dorsal sepal 15–20 mm in length in C. sieboldopsis vs. 22–30 mm in C. sieboldii, petals 15–17 in length vs. 19–24 mm), longer spurs (12–14 mm vs. 6–8 mm), lip mid-lobe nearly rectangular with emarginate apex (vs. elliptic with mucronate apex), disc with 3 ridges and the proximal ends of the lateral 2 ridges enlarged with light reddish spots and minute white hairs (vs. disc with 5 ridges and 2 rows of white short hairs at base), pollinia equal in size (vs. unequal in size with the lower 4 smaller and the upper 4 larger).

China. Jiangxi Province: Ji’an City, Jinggangshan Mountain, Jinggangshan National Nature Reserve, in the valley, near margins of evergreen broad-leaf forest, 26°25'17"N, 114°35'02"E, ca. 540 m a.s.l., 19 April 2017, B.Y.Yang 095 (Holotype: CSH!; Isotypes: JXU!).

Figure 2. 

Line drawing illustration of Calanthe sieboldopsis B.Y.Yang & Bo Li, sp. nov. A habit B flower C column and lip (top view) D lip (bottom view) E ovary, column, lip and spur (lateral view) F dorsal sepal G lateral sepals H petals I column, rostellum and anther cap (uncovered) J anther cap (top view) K pollinia.

Plants 35–45 cm tall. Rhizome elongate, thick. Pseudobulbs small, inconspicuous, obscured by the bases of the leaves, with 3–5 basal sheaths. Leaves 4–7, well developed and spreading at anthesis, not deciduous; blade broadly elliptic, 14–28 × 6.5–9.0 cm, apex acute; petiole-like base 9.5–16 cm long, usually forming a pseudostem, 8.5–10 cm long, 1.0–1.5 cm in diam. Scape arising from leaf axil, 30–45 cm tall, sparsely puberulent; rachis 15–25 cm long, laxly 8–11-flowered; floral bracts persistent, lanceolate, 5.0–8.5 mm long, puberulent, apex acuminate. Flowers bright yellow, large, slightly fleshy, glabrous except for lip base; pedicel and ovary 18–20 mm long, minutely puberulent. Dorsal sepal elliptic, 15–20 × 5.0–6.5 mm, apex acute; lateral sepals narrowly oblong, 12–15 × 4–6 mm, apex acute. Petals obovate-lanceolate, 15–17 × 4.5–5.5 mm, base narrowed, apex acute; lip adnate to entire length of column wings, spreading horizontally, yellow, mottled red at base, deeply 3-lobed; lateral lobes oblong-elliptic or falcate-obovate, oblique, 6.5–8.0 × 4.5–5.5 mm, apex obtuse-rounded; mid-lobe nearly rectangular, 6.0–8.5 × 4.5–5.5 mm, apex emarginate; disc with 3 ridges, extending to middle of mid-lobe; the proximal ends of the lateral 2 ridges enlarged, with light reddish spots and minute white hairs; spur curved, cylindrical, 12–14 mm, inside puberulent. Column 5.0–6.0 mm, thick, wings decurrent and connecting to ridges on disc; rostellum 2-lobed; anther cap beaked; pollinia 8, clavate, equal in size, grouped into two clusters, each with a short caudicle, 0.5 mm long, attached to an elliptic viscidium.

Flowering was observed from early April to early May and fruiting from late April to early June.

The species is currently known only from two sites: one is the type locality in Jinggangshan National Nature Reserve, Jinggangshan Mountain, Luoxiao Mountains of Jiangxi Province and another in Xianyueshan Mountain of Liling City, Hunan Province (Figure 3). The two localities belong to the same large mountain range, Luoxiao Mountains, which are the provincial border of Jiangxi and Hunan provinces. Plants of both populations grow in wet valleys and near margins of evergreen broad-leaf forest at elevations of 400–600 m a.s.l.

Figure 3. 

Distribution map of Calanthe sieboldopsis (blue and green circles show the type locality and another occurrence, respectively) and C. sieboldii (purple and orange squares show historical records and the recently-discovered localities, respectively).

The specific epithet “sieboldopsis” is a combination of two phrases “siebold” (which is derived from the specific epithet of the species C. sieboldii) and “opsis” (which means resembling), indicating that C. sieboldopsis is most similar to C. sieboldii.

The species is only known from two separate localities in the Luoxiao Mountains range: one is in the Jinggangshan National Nature Reserve of Jiangxi Province, where its habitat is well protected and 21 mature individuals were counted; the second locality in Xianyueshan Mountain of Liling City, Hunan Province, is not located in a nature reserve and only five flowering individuals have been found. Based on our observations, deforestation is the main threat to the Hunan population. Though there are probably other populations that have not been discovered in the Luoxiao Mountains or adjacent regions, we have carried out thorough field surveys in Jiangxi Province for more than 10 years and, so far, found that the total mature individuals of C. sieboldopsis are much less than 50, thus the new species should be categorised as critically endangered (CR) under criteria D, following the Guidelines for Using the IUCN Red List Categories and Criteria (IUCN 2019).

Calanthe sieboldopsis: China. Hunan Province: Liling City, Xianyueshan Mountain, in the valley, 27°38'02"N, 113°27'22"E, 410 m a.s.l., 11 April 2018, B.Y.Yang 119 (JXU!); Jiangxi Province: Ji’an City, Jinggangshan National Nature Reserve, 26°25'17"N, 114°35'02"E, 540 m a.s.l., 25 April 2018, B.Y.Yang 122 (JXU!); ditto, 10 April 2019, B.Y.Yang 151 (JXU!).

Calanthe sieboldii: China. Hubei Province: Shennongjia Forestry District, Shennongjia National Nature Reserve, roadside, 31°23'51"N, 110°34'55"E, 475 m a.s.l., 11 August 2008, D.G.Zhang zdg7268 (JIU!); Shennongjia Forestry District, Yangri Village, mountain slope, in evergreen broad-leaf forests, ca. 2000 m a.s.l., 15 May 2012, D.G.Zhang zdg6189 (JIU!); Hunan Province: Linwu County, Xishan National Forest Park, in evergreen broad-leaf forests, 570 m a.s.l., 4 April 2014, X.L.Yu et al. 140404 (six sheets, CSFI!); Jiangxi Province: Ji’an City, Qingyuan District, Tianmashan Mountain, in forests, 26°40'54"N, 115°24'19"E, 560 m a.s.l., 15 April 2015, B.Y.Yang JA201504017 (JXU!); ditto, 22 April 2019, B.Y.Yang 154 (JXU!); Taiwan Province: Xinzhu County, Jianshi Town, along Shihlu Historic Road, near Paishih Drawbridge, on steep rocky slope, 24°33'18"N, 121°13'38"E, 1420 m a.s.l., 21 February 2002, Y.Y.Huang 979 (HAST!); ditto, Jianshi Town, Litungshan Mountain, way to Nalo-Yulao, 7 March 1987, H.J.Su 7772 (HAST!).

When preparing the Orchidaceae account for Flora of Jiangxi, we have carried out many years of field surveys, resulting in the discovery of a large number of new records for Jiangxi and a few taxa new to science (e.g. Yang et al. 2017, Wang et al. 2018). In Calanthe, 11 species have been found in Jiangxi Province, including the new species C. sieboldopsis and the newly-recorded C. sieboldii (Wang et al. 2018). Though in the latest revision of the genus Calanthe, C. sieboldii was reduced as a synonym of C. striata Lindl. (Clayton and Cribb 2013), this taxonomic treatment was not widely accepted in recent literature (e.g. Zhai et al. 2014; Zhou et al. 2016; Jin et al. 2019), thus we here recognise C. sieboldii as a separate species. Calanthe sieboldii was previously mainly reported from Ryukyu Islands of Japan, from Korea and from Hunan and Taiwan provinces of China (Chen et al. 2009), but it was recently discovered from Shennongjia National Nature Reserve of Hubei Province (Xie et al. 2017) and Ji’an City of Jiangxi Province (Wang et al. 2018) (Figure 3). Calanthe sieboldopsis is superficially most similar to C. sieboldii because both of them are characterised by having large bright yellow flowers, but they are clearly different from each other in flower size, spur length, shape and characteristics of mid-lobes of lips and pollinia size (Figure 1). Amongst these differences, the shape of the lip mid-lobe and the characteristics of the disc could be used as the main identification trait to distinguish the two species.