WII-ADA1353 (Fig. 3A, 4A–F), adult male, collected from ~300 m south of Kamala Valley Beat (27°27′34″ N; 96°25′40″ E; elevation 648 m a.s.l.; Fig. 1), Namdapha, Changlang district, Arunachal Pradesh on 14 May 2022 by Abhijit Das, Bitupan Boruah and Vijayan Jithin.

Adult males (WII-ADA1352, WII-ADA1354-1356) (Figs 3B–K, 4G–K) collected from the same locality (Fig. 1) and on the same date along with the holotype; WII-ADA1400, adult male collected from the same locality on 18 May 2022.

A small sized rhacophorid frog with SVL 23.6–26.5 mm (n = 6) in adult males, body slender, snout pointed, head longer than wide, nostril closer to snout tip than eye, internasal distance shorter than inter upper eyelid distance, tympanum and supratympanic fold distinct, limbs slender, digits with large disc, circum-marginal groove on disc present, nuptial pad present on first finger in males, webbing absent between fingers, vomerine ridge absent, dorsal skin on snout, head, dorsum and limbs with spinules of different size, belly granular, dorsally chartreuse green with brown spots of irregular shape and size, upper eyelids dark brown, a broad brown stripe along canthus rostralis from anterior corner of the eye to tip of the snout covering the nostril, another brown stripe from posterior edge of the upper eyelid along supratympanic fold running dorso-laterally to one third of the trunk, white patches of irregular shape and size on the lateral side of the head below mid-eye, below tympanum in the mandibular region, continues along flank to groin, below skin semi-transparent, light green with large white patch covering middle of throat, chest, axilla and anterior half of the belly, brown cross bars on fore-arm, thigh and tibia present.

A small sized frog (SVL 24.5 mm) (Figs 3A & 4A–F); body slender; head longer than wide (HW/HL = 0.89); snout pointed in dorsal view and obtuse in profile, slightly projected beyond the lower jaw in ventral view; snout one third of the head length (SL/HL = 0.38) and shorter than eye length (SL/EL = 0.80); nostril small, laterally positioned, oval in shape, closer to tip of the snout than eye (NS/EN = 0.93); inter-nasal width smaller than inter-upper eyelid width (IN/IUE = 0.83) and smaller than upper eyelid width (IN/UEW = 0.89); upper eyelid width smaller than inter-upper eyelid width (UEW/IUE = 0.93); eyes comparatively large (EL/HL = 0.47); canthus rostralis distinct, sharp and vertical; loreal concave, tongue bifid and dorsal surface with tiny tubercles, vomerine teeth absent, choanae oval, tympanum distinct, oval in shape (HTYD/VTYD = 0.75), close to the eye (TE = 0.20 mm); supratympanic fold distinct; forelimbs slender, forearm shorter than hand length (FAL/HAL = 0.86); third finger is longest, relative finger length FIL<FIIL<FIVL<FIIIL; finger disc large and elliptical in shape, disc of the finger II, III and IV wider than horizontal tympanic diameter; disc with circum-marginal groove (Fig. 4H); terminal knuckle distinct; subarticular tubercles distinct, large and round, upper one on finger III and IV are larger than the lower one, subarticular tubercles FI = 1, FII = 1, FIII = 2, FIV = 2; webbing between fingers absent; hindlimbs slender; shank length more than half the snout-vent length (SHL/SVL = 0.57) and slightly longer than thigh length (TL/SHL = 0.94); foot length greater than tarsus length (TarL/FOL = 0.65); fourth toe is the longest, relative length among of the toes TIL<TIIL<TIIIL<TVL<TIVL; toe discs relatively smaller than those of fingers, nearly round, with circum-marginal groove, subarticular tubercles large, round and distinct, the bottom subarticular tubercles on toe III, IV and V are smaller than the upper ones; webbing between toes small, I 1— 1 ½ II ½ —2 III 1⁺— 2- IV 2— ½ V.

Dorsal skin on snout, head and back shagreened with dense spinules (Fig. 3D), those on upper eyelids, supratympanic fold and dorsolateral side of the back are slightly larger (Fig. 3F); lateral side of the head smooth, two flat rictal glands behind the angle of jaw in the mandibular region, tiny tubercles below supratympanic fold behind the tympanum; flank smooth; limbs dorsally smooth with scattered spinules; dermal fringe present along all fingers (Fig. 4E,G), palm with large granules, inner, middle and outer palmer tubercles present, fine granular nuptial pad present on first finger (Fig. 4I); flat granules along ventrolateral side of forearm and tarsus; ventrally throat smooth, chest nearly smooth, a few granules sparsely present; belly granular (Fig. 3H,I), those posteriorly more prominent, thighs granular at the basal half, distinct granules also present around the vent; tibia smooth; ventral side of the foot with many granules, supernumerary tubercles not visible; inner metatarsal tubercle distinct and elongated, outer metatarsal tubercle absent; dermal fringe along the toes present (Fig. 4D).

Dorsally head, dorsum and limbs chartreuse green with brown spots of irregular shape and size (Fig. 3). Those brown spots on the forearm, thigh and tibia are in the form of short cross bars. Upper eyelids dark brown; a broad brown stripe originating from anterior corner of the eye to the snout tip, covering canthus rostralis and narial opening. Another brown stripe along the supratympanic fold which continues dorsolaterally to the middle of trunk; diffused posteriorly and broken. Head laterally green, white patches of irregular size and shape starting below mid eye to rear of mandible below the level of tympanum. Iris golden yellow with dense brown marbling. Digits slightly paler than dorsal colour or more yellowish, brown spots continue along the fourth digit of forelimb and fourth and fifth digits of hindlimb, webbing between fourth and fifth toe brown. Vent surrounded by brown marbling and large irregular white spots around it (Fig. 3K). White patches are present on the axilla, continues through flank to the groin, shape and size of the white patches are irregular on both sides. Ventrally green, similar as that of dorsal; white spots on gular region, a large white patch spreading over middle of the gular region, chest and anterior half of the belly (Fig. 3H). White marbling present along the ventrolateral side of the forearms. White marbling along the tarsus, along fifth toe and upper part of the groin. Small brown spots present on the ventral side of the fourth and fifth toe and web between them brown.

Dorsally head, dorsum and limbs creamy white with brown markings; white patches on lateral side of the head and on flank not visible; ventrally throat, chest belly and limbs pale creamy white, no white patches visible; brown markings on ventral side of the foot visible as in life (Fig. 4).

Measurements of the type series are given in Table 2. Dorsal colour slightly varied among the individuals. Number of brown spots and size on dorsal skin varied among the individuals (Appendix 2). Furthermore, the pattern and size of the white patches on the lateral and ventral side of head and body varied among the individuals.

Comparative mensural and meristic characters are given in Table 3. The new species Gracixalus patkaiensissp. nov. differ from the species of the “Clade II” (G. ananjevae (Matsui & Orlov, 2004), G. carinensis (Boulenger, 1893), G. guangdongensis Wang, Zeng, Liu & Wang, 2018, G. jinggangensisZeng et al., 2017, G. jinxiuensis (Hu, 1978), G. nonggangensisMo et al., 2013, G. sapaensis Matsui, Ohler, Eto & Nguyen, 2017, G. tianlinensisChen et al., 2018, G. triengRowley et al., 2020, G. yunnanensisYu et al., 2019, G. ziegleriLe et al., 2021 by its chartreuse green dorsum and pointed snout (vs. brown dorsum and rounded snout) (sensu, Rowley et al., 2011). Furthermore, it differs by its small body size (SVL = 23.6–26.5 mm, n = 6) in adult males vs. large body size (SVL = 27.9–33.8 mm in G. jinggangensis, 29.9–35.3 mm in G. nonggangensis, 37.2– 41.4 mm in G. trieng, 30.3–35.9 mm in G. tianlinensis, 28.1–30.5 mm in G. ziegleri, 32 mm in G. ananjevae).

Further the new species differs from G. ananjevae by its slender body (vs. robust body), head length greater than width (vs. head wider than its length), snout shorter than eye length (vs. snout length equal to eye length), snout pointed (vs. slightly pointed), webbing on fingers absent (vs. poorly developed web present), dorsal surface of legs with scattered spinules (vs. smooth), a large white patch on belly (vs. absent), dorsum with irregular brown spots (vs. dorsum with a dark brown marking starting between eyes and bifurcating posteriorly).

Gracixalus patkaiensissp. nov. differs from G. carinensis by pointed snout (vs. rounded snout), presence of spinules on dorsum (vs. absent), webbing on fingers absent (vs. rudimentary web present), white patches on lateral side of head, flank and belly present (vs. absent), x-shaped mark on dorsum absent (vs. present).

Differs from G. guangdongensis by its slender body (vs. robust body), spinules on eyelids present (vs. absent), absence of inverse Y-shaped dark brown marking on dorsum (vs. present), lateral surface of head smooth (vs. tubercular), snout length smaller than eye length (vs. snout length greater than eye length), white patches on lateral side of head, flank and belly present (vs. absent).

Differs from G. jinggangensis by head length greater than width (vs. head wider than its length), presence of spinules on eyelids and dorsum (vs. absent), absence of inverse Y-shaped dark brown marking on dorsum (vs. present), nuptial pad on second finger in males absent (vs. present), white patches on lateral side of head, flank and belly present (vs. absent).

Differs from G. jinxiuensis by the presence of spinules on dorsum (vs. scattered tubercles present), white patches on throat, chest and belly present (vs. absent).

Differs from G. medogensis (Ye & Hu, 1984) by head width smaller than its length (vs. head width greater than its length), snout pointed (vs. rounded), presence of spinules on dorsum (vs. dorsum smooth), irregular brown spots present on dorsum (vs. an inverse “V” shaped mark present on dorsum), white patches on lateral side of head, flank and belly present (vs. absent).

Differs from G. nonggangensis by snout length smaller than eye length (vs. snout longer than eye diameter), dorsally chartreuse green (vs. yellowish-olive), dark brown spots on throat and belly absent (vs. present), white patches on lateral side of head, flank and belly present (vs. absent).

Differs from G. sapaensis by the presence of distinct tympanum (vs. indistinct), single external vocal sac present (vs. paired vocal sac present), dorsum with spinules (vs. nearly smooth), white patches on throat, chest and belly present (vs. absent).

Differs from G. tianlinensis by its slender body (vs. robust), head length greater than head width (vs. head length less than width), Y-shaped dark brown marking on dorsum absent (vs. present), nuptial pad on second finger in males absent (vs. present).

Gracixalus patkaiensissp. nov. differ from G. trieng by the presence of spinules on dorsal surface of head, back and limbs (vs. absent), distinct and broad cross bars on limbs absent (vs. present), interorbital crossbar absent (vs. present), brown spots of irregular size and shape present on dorsal surface of head, back and limbs (vs. inverse Y- shaped marking present on dorsum), white patches on lateral side of head, flank and belly present (vs. absent).

Differs from G. yunnanensis by slender body (vs. robust), inversed Y-shaped dark brown marking on dorsum absent (vs. present), white patches on lateral side of head, flank and belly present (vs. absent).

Differs from G. ziegleri by head length larger than width (vs. head wider than long), spinules present on upper eyelids (vs. absent), inverse Y-shaped dark brown marking on dorsum absent (vs. present).

Differs from G. truongiTran et al., 2023 by smaller body size of males, SVL = 23.6–26.5 mm (vs. SVL = 32.2–33.1 mm), snout pointed (vs. rounded), presence of spinules on dorsum (vs. dorsum smooth), presence of spinules on upper eyelids (vs. absent), head longer than width (vs. head wider than its length), inverse Y-shaped dark brown marking on dorsum absent (vs. present). white patches on lateral side of head and flank present (vs. absent).

The new species differs from species with greenish dorsum of the “Clade I” (sensu Rowley et al. 2011) as follows.

Gracixalus patkaiensissp. nov. differs from G. seesomMatsui et al., 2015 by the presence of spinules on dorsal surface of head and back (vs. smooth dorsum), snout length smaller than eye length (vs. snout longer than eye diameter), upper eyelids dark brown (vs. upper eyelids without dark patch), tubercles on flank absent (vs. large tubercles present on flank), white patches on lateral side of head present (vs. absent).

Differs from Gracixalus quangiRowley et al., 2011 by snout length smaller than eye length (vs. snout length larger than eye length), head length greater than width (vs. head length and width equal), the absence of tibio-tarsal projection (vs. present), serrated dermal fringe along forearm absent (vs. present), brown interorbital cross bar and X- shaped marking on dorsum absent (vs. present), brownish black spots on the flank and ventral surface of thighs absent (vs. present), white patches below the eye and mandibular region below the level of tympanum (vs. large opaque, pale turquoise patch under the supratympanic fold and eyes), webbing between the fourth and fifth toes brown (vs. all webbing, dorsal and ventral surface of the foot black).

Differs from G. quyeti (Nguyen et al., 2008) by snout pointed (vs. rounded), dorsal colour chartreuse green with brown spots (vs. mossy green without brown spots), white patches below the eyes, flank and belly present (vs. absent).

Differs from G. supercornutus (Orlov et al., 2004) by absence of large horn-like projections on upper eyelids, dorsum and along forearm and tarsus (vs. present), broad brown interorbital crossbar and dorsolateral stripes on dorsum absent (vs. present).

Gracixalus patkaiensissp. nov. is morphologically more close to G. gracilipes (Bourret, 1937). However, it differs from G. gracilipes by genetic divergence of 4.0–5.0% and by the following morphological characteristics. The new species differ from G. gracilipes by the absence of interorbital cross bar and distinct X- shaped marking on dorsum (vs. present; Bourret 1942; Orlov et al. 2004, fig. 17; Delorme at al. 2005, fig. 7; Rowley et al. 2011, fig. 8D; Calphotos: Benjamin Tapley/ZSL), webbing between fourth and fifth toe brown (vs. all webbing on brown; Rowley et al., 2011, fig. 8D), a few scattered brown spots on fourth and fifth toe (large brown patch covering fourth and fifth toe; Rowley et al., 2011, fig. 8D), tympanic region green (vs. tympanic region including tympanum may be brown; Rowley et al., 2011, fig. 8D; Calphotos: Benjamin Tapley/ZSL).

Ecologically G. gracilipes is distributed in mid elevations between ~1,200–2,500 m a.s.l. (Bain & Nguyen 2004; Fellowes & Hau 1997; Orlov et al. 2004; Frost 2022) while the new species is known only from lowland evergreen forest at an elevation of 648 m a.s.l.

Gracixalus patkaiensissp. nov. differs from G. lumariusRowley et al., 2014 the only species with brown or yellow dorsum of the clade I of Rowley et al. (2011) by smaller body size, SVL = 23.6–26.5 mm (n = 6) in adult males (vs. SVL 38.9–41.6 mm), pointed snout (vs. rounded snout), dorsal surface of hindlimbs with scattered spinules (vs. smooth), spinules absent on lateral side of the head (vs. present), tympanum and supratympanic fold distinct (vs. indistinct), white patches on lateral side of head, flank and on ventrum present (vs. absent).

We named the species after Patkai hills range where the type locality of the new species lies within Namdapha Tiger Reserve. The specific epithet “patkaiensis” is a noun in apposition.

Patkai green tree frog.

Currently the species is only known from a single locality in Kamala Valley Beat, popularly known as 25 mile in the Namdapha Tiger Reserve. It may occur in similar microhabitats in the forest interior of the tiger reserve.

Advertisement call of Gracixalus patkaiensissp. nov. consists of highly variable non-stereotype and non-pulsatile call types, ranging from a relatively longer call “whistle” with narrow frequency bands to short call “click” (Fig. 5) with wide frequency band. Number of calls among the call groups varied between 3–16 (n = 16). Whistles were variable in structure within the call group or among the call groups although clicks are broadly similar in structure. At an ambient temperature 22.8°C, duration of the whistles varied from 45–229 ms (123.26 ± 67.97 ms, n = 23) and duration of the clicks ranged from 7–65 ms (16.95 ± 10.65 ms, n = 108). Call repetition rate varied 1.15–18.87 calls/minute (8.14 ± 6.88 calls/minute, n = 17). Inter-call intervals ranged from 5–1274 ms (160.37 ± 231.55 ms, n = 115). Fundamental or dominant frequency of the whistles ranged between 4.35 kHz to 4.61 kHz (4.51 ± 0.06 kHz, n = 22) and dominant frequency of the clicks ranged from 3.1 kHz to 4.61 kHz (4.22 ± 0.27 kHz, n = 108). Clear harmonics were visible only in the whistles. Temporal order of the call types was not constant. A comparative account of acoustic characters of Gracixalus species is given in Table 4.

We came across a calling aggregation of the new species on 14 May, 2022 between 17:30 hrs and 19:00 hrs along a forest trail. The forest tree layer in the habitat was dominated by Dipterocarpus retusus and the shrub layer by Bambusa sp. and Calamus sp. (Fig. 6). The 10x10 m site in the area was characterized by a canopy cover of ~70% and clayey soil, with a first-order stream associated with a marshy habitat. The area also had a few large fallen logs in an advanced decaying stage. The male individuals of the species were observed calling from leaves and twigs of shrub, fern leaf sheaths, Zingiber leaves, lamina and rachis of rattan palms (Calamus sp.) at a height of ~ 0.5–2 m above the ground or shallow water. Other frog species present in the area were Limnonectes sp., Kurixalus sp., Raorchestes sp. Rhacophorus rhodopus Liu & Hu, 1960, Xenophrys ancrae (Mahony, Teeling & Biju, 2013), Microhyla eos Biju, Garg, Kamei & Maheswaran, 2019 and Duttaphrynus sp. The pool in the spot harboured the tadpoles of Microhyla sp. and Rhacophorus rhodopus. Adult frogs were active only during rainy nights. Air temperature and relative humidity were recorded as 22.7°C and 93.8% respectively at the time of observations. During our next visit to this site in September 2022 no breeding activity was observed in the area nor any individual was encountered in the spot.