Gastrochilus prionophyllus, which was previously not validly published, is here validated. The species is described along with illustration and photos. Morphologically, the long and pendulous stem and distichous leaves of this new species indicate that it belongs to the sect. Microphyllae. It is unique in having thick fleshy leaves and margin significantly serrate, small flowers, reniform epichile and margin with dentations, thickened cushion on the central epichile and subconic hypochile. Meanwhile, a preliminary conservation status assessment according to IUCN Red List categories and criteria is given to the new species.

Orchidaceae, section Microphyllae, Gastrochilus, taxonomy, Yunnan

The genus Gastrochilus D. Don was established in 1825 (Epidenroideae; Vandeae; Aeridinea), which includes more than 62 species collectively distributed from India and Sri Lanka throughout Indochinese Peninsula, extending southwards to Indonesia and eastwards from China to Southern Japan (Chen et al. 2009; Kumar et al. 2014; Govaerts et al. 2016; Raskoti 2016; Averyanov et al. 2018; Liu et al. 2016, 2019; Liu and Gao 2018,). Some studies had speculated that Gastrochilus spread from tropical regions to temperate alpine regions (Fan et al. 2009; Liu et al. 2019). China is the diversity center of Gastrochilus and contains 42 species, of which 22 species are recognized as endemic to China, mainly in the Southern and the Southwestern parts of the country (Tsi 1996; Chen et al. 2009; Kumar et al. 2014; Liu et al. 2016, 2019; Liu and Gao 2018).

During our field investigation in the limestone forest of Southeast Yunnan Province, a species of Gastrochilus with serrate leaf was collected. After reviewing the relevant literature, two of the authors agreed the collection shares an identical morphology and provenance to the species presented and named previously as G. prionophyllus in The Wild Orchid in Yunnan (Xu et al. 2010). But it was never validly published, as neither provided a description nor cited the type specimen according to the International Code of Nomenclature for algae, fungi and plants (Shenzhen Code) (Turland et al. 2018). Here, the name of Gastrochilus prionophyllus is validly published. In addition, an illustration, a note on distribution, and affinities with other closely resembling species and IUCN conservation status are provided.

Morphological observations of the new species were based on living plants (five individuals) and dried herbarium specimens (three specimens kept in the herbaria of HITBC) from two flowering seasons (2015 to 2016). All morphological characters were measured by using the vernier caliper. Both herbarium specimens and fresh material of G. distichus and G. corymbosus were examined. The conservation status of the new species was evaluated based on the guidelines of the International Union for Conservation of Nature (IUCN 2017).

Note: The long and pendulous stem of this new species indicate that it belongs to the sect. Microphyllae (Tsi, 1996), and these species are easily confused by having similarly vegetative and floral characters, especially between G. distichus and G. pseudodistichus. Such as the specimens of G. distichus: QTT 73-896 (KUN!), ETM 4115 (KUN!) and Wang 63369 (AMES!) all were misidentified as the G. pseudodistichus. Although the new species is similar to G. distichus and G. corymbosus in vegetative and floral characters, it differs from G. distichus by having thick fleshy leaves with significant serrates margin, smaller flowers and sepals size less than 4 mm, and thickened cushion on the central epichile (vs fleshy leaves and margin entire, flowers large and sepals size more than 5 mm, and slightly thickened cushion on the central epichile in G. distichus) (Chen et al. 2009) (see Table 1 and Figure 3); differs from G. corymbosus by subumbellate inflorescence, reniform epichile and margin with dentations, orbicular central cushion on the epichile and subconic hypochile (vs corymb inflorescence, suborbicular epichile and margin entire, diamond-shaped cushion on the epichile and subcupular hypochile in G. corymbosus) (Das and Chanda 1988) (see Table 1 and Figure 3).

Figure 3. 

A Gastrochilus corymbosus (A-1 Plant A-2 Inflorescence and flowers) B G. distichus (B-1 Plant B-2 Inflorescence and flowers) C G. prionophyllus (C-1 Plant C-2 Inflorescence and flowers) (Photographed by Q. Liu).

This work was supported by the National Natural Science Foundation of China (Grant no. 31500164) and Southeast Asia Biodiversity Research Institute, Chinese Academy of Sciences (Grant No. Y4ZK111B01) to Q. Liu and CAS 135 program (Grant No. 2017XTBG-F03). We are grateful to B. Pan for the excellent illustration and thanks to Y. P. Wu, Y.L. Li, T.P. Lin, X.H. Jin, L.V. Averyanov and H.A. Pedersen for access to literature and X. B. Guo for assistance in the field.