Calanthe sieboldopsis (Orchidaceae, Epidendroideae, Collabieae), a new species from Luoxiao Mountains, eastern China.

Abstract Calanthe sieboldopsis, a new species, is here described and illustrated from Luoxiao Mountains, Jiangxi Province, eastern China. It is morphologically similar to C. sieboldii Decne. ex Regel, but differs from the latter in having smaller flowers, longer spurs, rectangular mid-lobes with emarginate apex (vs. elliptic mid-lobes 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) and pollinia equal in size (vs. unequal in size). A preliminary risk-of-extinction assessment, according to the IUCN Red List Categories and Criteria, is given for the new species.


Introduction
Calanthe R. Br. is the largest genus of the tribe Collabieae (in the subfamily Epidendroideae), according to the updated classification of the orchid family (Chase et al. 2015). The genus contains about 160 species of terrestrial orchids, commonly oc-curring in tropical, subtropical and temperate regions of Asia, Africa and the Pacific islands (Clayton and Cribb 2013), with a concentrated distribution of more than 50 species in China (Chen et al. 2009). Based on the latest infrageneric treatment, Calanthe was subdivided into five sections, viz., sect. Alpinocalanthe J.W. Zhai (Zhai et al. 2014). In the last two decades, new species of Calanthe have been discovered in China (Ren et al. 2011;Huang et al. 2015;Guo et al. 2017;Yu et al. 2017), Korea (Oh et al. 2015), Myanmar (Kurzweil 2013) and the Philippines (Naive 2017) and more discoveries can be expected, indicating that the diversity of Calanthe in Asia has not yet been fully revealed.
In order to ascertain the orchid diversity in Jiangxi Province of eastern China for preparing the Orchidaceae account of Flora of Jiangxi, we have carried out continuous field surveys from 2008 to 2019. When identifying specimens collected from Jinggangshan National Nature Reserve in 2017, we encountered an unknown collection of Calanthe, which is superficially similar to C. sieboldii Decne. ex Regel, but differs in having smaller flowers, longer spurs and emarginate lip mid-lobes with different characteristics of the disc (Figure 1). After carefully comparing the plant with all known congeneric taxa and consulting the relevant literature, we confirm that the plant represents an undescribed new species which is described here.

Methods
The locality of the new species in Jinggangshan National Nature Reserve of Jiangxi Province was revisited in April 2018 and one flowering individual was collected for the line-drawing. Expecting to discover more populations of the new species, we expanded our field surveys from Jinggangshan Mountain to the whole mountain range, Luoxiao Mountains, in 2018 and 2019 and finally found an additional population on Xianyueshan Mountain of Hunan Province. The morphological description is based on flowering plants in the two populations and morphological measurements were taken using a ruler and a Vernier caliper from at least 10 individuals. Flowers were dissected and photographed under a stereo dissecting microscope (StereoZoom Leica S8 APO, Leica Microsystems 2017).
Herbarium specimens of the genus Calanthe were examined at IBK, IBSC, JIU, JXU, KUN, LBG, NAS, PE and SYS (for herbarium acronyms, see Index Herbariorum: http://sweetgum.nybg.org/ih). Fresh plants of C. sieboldii, the most similar species of the new species, were collected from Tianmashan Mountain of Jiangxi Province in 2019 for morphological comparisons. The distribution map was prepared using geo-referenced locations, data obtained from herbarium specimens and our own field observations. The conservation status of the new species was evaluated, based on the guidelines of the International Union for Conservation of Nature (IUCN 2019). Diagnosis. 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).
Phenology. Flowering was observed from early April to early May and fruiting from late April to early June.
Distribution. The species is currently known only from two sites: one is the type locality in Jinggangshan National Nature Reserve, Jinggangshan Mountain, Luoxiao Etymology. 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.
Preliminary conservation assessment. 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)  Note. 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 super-ficially 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.