The taxonomic identities of Pholidota wenshanica and P. subcalceata (Orchidaceae, Coelogyninae)

Abstract P. wenshanica S.C.Chen & Z.H.Tsi and P. subcalceata Gagnep. have long been recognized as synonyms of P. leveilleana Schltr. In the present study, detailed morphological comparisons suggest that specimens referred to as P. wenshanica and P. subcalceata differ significantly in both vegetative and floral characters from those of P. leveilleana. Here we resurrect P. wenshanica and P. subcalceata as independent species. Key diagnostic characters essential for delineating identities of these species are presented.


Introduction
The orchid genus Pholidota Lindl. ex Hook. was established by Hooker (1825: pl. 138). The generic epithet is from the Greek pholidotos, referring to the imbricate bracts of the inflorescence of some species (Pridgeon et al. 2005). As currently circumscribed, the genus is classified within the subtribe Coelogyninae, subfamily Epidendroideae, comprising about 30 species, distributed from Pakistan, India, Sri Lanka, Nepal, Bhutan, Myanmar, S China, Taiwan, Indo-China and the Malesian region into the SW Pacific (Seidenfaden 1986;de Vogel 1988;Seidenfaden and Wood 1992;Pearce and Cribb 2002;Pridgeon et al. 2005).
The taxonomic status of the Chinese species P. wenshanica S.C. Chen & Z.H.Tsi (1988: 7) has long been in doubt. Soon after its publication in the same year, this species has been placed in synonym with P. leveilleana Schltr. (1913: 107) by de Vogel (1988) while revising the genus Pholidota. There have been no further references to that species, except in the protologue (Chen and Tsi 1988) and subsequent reports (Chen and Tsi 1998;Chen 1999). In Flora Reipulicae Popularis Sinicae, Chen (1999) regarded this species as an independent species and consistently named P. wenshanica. However, in the revised edition Flora of China, Chen and Wood (2009) followed the treatment of de Vogel (1988) and reduced it as the synonym of P. leveilleana with some doubts. According to the addendum made by de Vogel (1988): " I have not seen the holotype, Tsi 223 (PE), but the description and the line drawings do agree so very well with P. leveilleana Schltr. that I am convinced that it is conspecific with that species". These more or less ambiguous treatments of P. wenshanica caught our attention.
Comparison of Pholidota specimens collected from different localities in China showed those representing P. wenshanica could be distinguished from P. leveilleana on the basis of several morphological characters recognized in this study. Further investigation revealed that a Vietnamese species P. subcalceata, which has been treated as a synonym of P. leveilleana, also differs in its unique characters. The present paper includes confirmation of the validities of P. wenshanica and P. subcalceata, assessments of diagnostic characters of these species and descriptions of newly recognized diagnostic characters.

Material and methods
To clarify the taxonomic status of Pholidota wenshanica in China, morphological studies were performed using specimens deposited at herbaria E, GXMG, IBK, IBSC, KUN, P and PE, and online databases such as JSTOR Global Plants (http://plants. jstor.org) and Chinese Virtual Herbarium (http://www.cvh.ac.cn/), with special focus on the type specimens. The only type of P. wenshanica was thoroughly examined and compared with various specimens of P. leveilleana from China including some type materials of its synonym P. subcalceata from Vietnam. Relevant literature, including the protologue, was consulted. We also conducted field investigations in the type localities of P. wenshanica and P. leveilleana. Living plants were collected and transplanted to the nursery of South China Botanical Garden (SCBG) for further observation. Measurements and photographs of the fresh material were made under a stereomicroscope Olympus MD-90. Herbarium abbreviations follow Index Herbariorum (Thiers 2015, http://sweetgum.nybg.org/science/ih/).

Results and discussion
Pholidota wenshanica S.C.Chen & Z.H.Tsi was described based on a specimen collected from Wenshan County, Yunnan (Chen and Tsi 1988). According to the protologue, this species is characterized by having fusiform-cylindrical pseudobulbs with two apical leaves, well-spaced on creeping rhizomes, lanceolate-oblong leaves.
Pholidota leveilleana Schltr. was described by Schlechter (1913) on the basis of a specimen collected by J. Esquirol from Guizhou (= Kweichow or Kouy-tchou), China. In the protologue, the author stated that the species is easily distinguished from the related species P. yunnanensis Rolfe (1903: 24) by unifoliate pseudobulbs (vs. twoleaved), loose (vs. tight) inflorescences with larger, white and crimson-red (vs. white) flowers. Unfortunately, the type sheet of P. leveilleana is nearly complete (Fig. 1D). In his monograph, de Vogel (1988) pointed out that the type specimen of P. leveilleana has only one leaf because it is a weakly developed plant, and thus this character cannot be used to distinguish these species. At the same time, he placed P. subcalceata Gagnep. (1950: 508) as the synonym of P. leveilleana. P. subcalceata was described based on two collections from Vietnam ( Fig. 1G, H). Gagnepain (1950) stated in the protologue that P. subcalceata has two linear to lanceolate leaves ca. 30 cm long. De Vogel's treatment has long been accepted until Chen (1999) noticed the clear difference in the leaf number of P. leveilleana. He placed P. leveilleana in section Pholidota, which is characterized by pseudobulbs with only one leaf.
Based on our close examination of the type specimens of P. wenshanica (Fig. 1A), P. leveilleana (Fig. 1D) and P. subcalceata (Fig. 1G, H), and of other specimens so named in E, P and PE ( Fig. 1), as well as the field observation, we are convinced that the leaf number is unlikely to change with growth in either P. leveilleana or P. wenshanica. Although the type specimen of P. leveilleana is not seemingly perfect, the morphology of specimen J. Esquirol no. 2088 ( Fig. 1D) actually conforms most closely to the diagnosis given in Schlechter (1913).
Morphological examinations indicate significant differences among these species. P. wenshanica is easily distinguished from the other two species by fusiformcylindrical pseudobulbs, much more slender (7−8 cm long) and well apart (2 cm intervals or distance), with two oblong-lanceolate leaves, up to 30 cm long and ca. 3.5 cm wide. In floral morphology, P. wenshanica can be readily distinguished from P. leveilleana by the flower number and size, as well as the details of flowers. The former has distinctly more (30-40) flowers arranged alternately on the almost straight rachis, whereas P. leveilleana has fewer (12-18) flowers on the weakly zigzag rachis (Fig. 2). On the other hand, the pseudobulbs of P. subcalceata are ovoid and close together, which are superficially similar to those of P. leveilleana, but carry two apical linear leaves. The size of its leaves varies from 15−30 cm in length and ca. 2.5 cm in width, whereas the leaves of P. leveilleana ca. 3.5 cm in width. In addition, P. subcalceata has synanthous inflorescence, with partially developed leaves at anthesis. A comprehensive morphological comparison among these species is presented in Table 1. An additional specimen's survey indicates that several collections previously identified as P. wenshanica, such as China-UK Expedition Team ASBK365 (IBK) (Fig. 1E) actually belong to P. leveilleana, with their unifoliate pseudobulbs closely placed.
In distribution, both P. wenshanica and P. leveilleana are endemic to southwestern China. P. leveilleana occur in W to N Guangxi and S Guizhou. P. wenshanica is currently only found in SE Yunnan and SW Guangxi. P. subcalceata is endemic to southern Vietnam. The more or less disjunct distributions clearly indicate that P. wenshanica and P. subcalceata should be considered as distinct species.  broadly rhombic-ovate, papyraceous, 4 × 6 mm, folded along the midrib, caduceus at anthesis. Flowers pinkish white, ca. 5 mm in diam., lip salmon-pink, tinged with yellowish-brown or orangish-brown blotches. Pedicel and ovary 3-4 mm long. Sepals subequal; dorsal sepal elliptic, 5 × 3 mm, apex acute, obscurely 7-nerved; lateral sepals ovate, slightly oblique, 5-6 mm long, strongly keeled on the back, apex shortly acuminate, obscurely 7-nerved. Petals ovate, 4 × 3mm, apex obtuse, obscurely 3-5-nerved; Labellum subovate in outline, 4-5 long; hypochile deeply saccated, with 4 prominent fleshy keels or carinae; epichile transversely elliptic, 4-5 mm wide, margin inconspicuously undulate, apex deeply notched into 2 broadly rounded lobes. Column stout, 2.5-3 mm long; apex narrowly winged, foot absent; stelidia obtuse, up margin with an inconspicuous rounded wing near the apex; anther incumbent, top retuse to rounded; pollinia 4 in 2 pairs, connected by caudicles to a sticky substance, pyriform, ca 0.5 by 0.4 mm; stigma broadly ovate; rostellum large, broadly triangular. Flowering in late November and early December. Capsule not seen. Distribution and habitat. Pholidota wenshanica is currently known only from SE Yunnan (Wenshan) and SW Guangxi (Longzhou), China, where it grows as epiphyte on tree trunks or as lithophyte on somewhat shady slopes or on the edge of forests, often in exposed places, with elevations ranging from 1200 m to 1500 m a.s.l.