Phalaenopsis medogensis (Orchidaceae, Epidendroideae, Vandeae), a new species from Xizang, China

A new species of Orchidaceae, Phalaenopsis medogensis , from Motuo, Xizang, is described and illustrated based on morphological characters and molecular phylogenetics analysis. Molecular phylogenetic analysis and morphological characters indicate that P . medogensis is close to P . deliciosa , P . gibbosa and P . lobbii , but differs from them by having triangular wings on the column foot, rhombic lip mid-lobe with a fleshy-horned appendage at the base, and concave lip lateral lobes, the lower part white with a deep purplish-red spot and hairy, the upper part pale yellow with dense rust spots.

There are about 24 species of Phalaenopsis in China (Zhou et al. 2021). During our fieldwork in Motuo County, Nyingchi City, Xizang Autonomous Region, China in 2022, an unknown species of Phalaenopsis was found in the evergreen broad-leaved forest along the Yarlungzangbo River. Based on morphological characters and molecular evidence, it was identified as a new species of Phalaenopsis and is described below.

Materials and methods
Morphological characters of the new species were observed, measured and photographed, based on living plants in Motuo, Xizang. Four markers, including one nuclear marker (nrITS) and three plastid markers (matK, trnL and trnL-F), were used in molecular systematics. Primers and amplification procedures of the four markers followed Deng et al. (2015). In total, 40 species in Phalaenopsis and seven species of Aeridinae (Suppl. material 1) were included in the molecular analysis. The conflict between nrD-NA and plastid DNA data was assessed in PAUA using the length difference test (ILD) (Darlu and Lecointre 2002). Two species, Aeranthes grandiflora Lindley and Podangis dactyloceras (Reichenbach) Schltr., were used as the outgroup, based on previous results (Chase et al. 2015;Li et al. 2019). Sequences were edited independently and assembled using SeqMan (https://www.dnastar.com/). Sequence alignment, model selection and super matrix construction were performed in the Phylosuite (Zhang et al. 2020). Bayesian Inference was inferred with MrBayes v. 3.2.7a on XSEDE in the CIPRES Science Gateway online web server (Miller et al. 2010). The model of partition selection was found in ModelFinder (Kalyaanamoorthy et al. 2017) with Corrected Akaike Information Criterion (AICc). GTR+F+I+G4 was selected as the best model for ITS and GTR+F+G4 for the three plastid markers. Two separate Markov Chain Monte Carlo (MCMC) analyses were performed, proceeding for 1,000,000 generations and sampling every 1000 generations. Maximum Likelihood (ML) analyses and model selection were performed in IQ-Tree 2 (Minh et al. 2020). Support values for the clade were estimated using 1,000,000 bootstrap replicates.

Results
The ILD test indicated that plastid markers and nrITS were not suitable for combined analysis. Phalaenopsis medogensis belongs to subgen. Parishianae and is close to P. deliciosa, P. gibbosa and P. lobbii, based on molecular phylogenetic analyses. The indicates that support at a node < 50%. Bayesian Inference and ML analyses of ITS showed that P. medogensis belongs to subgen. Parishianae with moderate to high support (Fig. 1, PP = 1, BS ML = 93.5). The Bayesian Inference of the three plastid markers showed that P. medogensis is sister to the group that includes P. deliciosa-P. lobbii with high support (Fig. 2 Diagnosis. Phalaenopsis medogensis is morphologically close to P. deliciosa, P. gibbosa and P. lobbii, but readily distinguished from them by its column foot having a pair of triangular wings, and a lip with concave subrectangular lateral lobes, that are white with a deep purplish-red spot in their lower part and hairy and pale yellow with dense rust-coloured spots in their upper part, and a rhombic mid-lobe with a fleshy horned appendage at base and grooved in the centre (Table 1).    Epiphytic plant. Roots greenish, elongate, flattened, densely verrucose and prostrate along the twigs or trunk. Stem very short. Leaf 1, oblong-elliptic, 7-10 × 3-4 cm. Inflorescences 1 or 2, suberect or arching, ca.12 cm long, unbranched, laxly 5-6 flowered; floral bracts ovate-triangular, 5-6 mm long. Flowers 1-1.2 cm in diameter,  yellow; sepals and petals pure yellow, lacking spots or other colouration. Dorsal sepal similar to petals, elliptic, ca. 7-8 × 5 mm; lateral sepals broadly triangular, ca. 10 × 6 mm. Petals long elliptic, ca. 9 × 5 mm. Lip 3-lobed; lateral lobes subrectangular, concave, almost boat-shaped, 2 × 4 mm, lower part white with a deep purplish-red spot and hairy, upper part pale yellow with dense rust-coloured spots; mid-lobe rhombic, ca. 10 × 7 mm, disc grooved, base with a fleshy protuberant appendage; appendage with 2-3 teeth on either side, apex with two long horns. Column subparallel to midlobe, ca. 5 mm long; column foot ca. 4 mm long, with triangular wings on both sides; anther cap yellow, hemi-spherical. Etymology. The epithet "medogensis" refers to the type locality of the new species, Medog County, Nyingchi City, Xizang Autonomous Region, China.
Distribution and habitat. Phalaenopsis medogensis is currently known only from the type locality in Motuo, Xizang, China. It is epiphytic on trunks and twigs at elevations of 700-900m along the hot valley of the Yarlungzangbo River.
Phenology. Flowering in March to April. Conservation status. Phalaenopsis medogensis grows in the tropical rain forest in Motuo County. At least one population of about 30 plants was discovered during our fieldwork. The habitat has been significantly damaged due to the development of agriculture and road construction. We tentatively assessed the risk of extinction of the Phalaenopsis medogensis as Critically Endangered (CR) under criteria B2ab(i, ii, iii, iv, v) according to the IUCN criteria version 15.1 (IUCN 2022).
Note. P. medogensis is similar to three species in subgen. Parishianae, namely, P. deliciosa, P. gibbosa and P. lobbii, but is readily distinguished from them based on morphological characters given in Table1