Trimeresurus loong Xu, Deng, Zhang, Nguyen, Poyarkov, Vogel & Peng, 2025

Xu, Yuhao, Deng, Jundong, Zhang, Tierui, Nguyen, Tan Van, Weng, Shiyang, Poyarkov, Nikolay A., Vogel, Gernot, Sun, Fanyue, Liao, Chencan & Peng, Lifang, 2025, A ‘ little dragon’ from Kunming City: a new green pit viper from Yunnan Province, China (Squamata, Viperidae, Trimeresurus), Zoosystematics and Evolution 101 (4), pp. 2267-2293 : 2267-2293

Trimeresurus loong Xu, Deng, Zhang, Nguyen, Poyarkov, Vogel & Peng sp. nov.

Tables 4 , 5 ; Figs 3 , 4 A, B , 5 , 6 , 7 , 8 , 9 B, C , 10 A, B , 11 A 1, A 2

Type material.

Holotype • QHU R 2025027 , adult male, collected from Qinglongxia , Anning City, Kunming City, Yunnan Province, China ( 25.0590°N, 102.3561°E; elevation 1,822 m asl.), on 15 September 2025 by J. D. Deng and Y. H. Xu .

Paratypes (n = 5) • QHU R 2025031 ( adult female), with same data as the holotype . • QHU R 2025028 ( adult male), collected on 22 September 2025 by J. D. Deng and Y. H. Xu ; • QHU R 2025029 ( subadult male) and • QHU R 2025032 ( adult female), collected on 27 May 2025 by J. D. Deng ; • QHU R 2025030 ( subadult male), collected on 21 September 2025 by J. D. Deng and Y. H. Xu; all from the same locality as the holotype .

Diagnosis.

The new species Trimeresurus loong sp. nov. is distinguished from all of its congeners by a combination of the following morphological characters: (1) first supralabial completely separated from the nasal scale; (2) hemipenis short and spinose, reaching the 10 th – 11 th subcaudal when fully everted; (3) moderate adult body size, with a maximum SVL of 601 mm in males and 657 mm in females; (4) dorsal scales in 19 (21 or 23) – 19–15 rows, keeled except for the outermost rows; (5) VS 150–151 in males and 157–158 in females; (6) SC 67–68 in males and 57–64 in females; (7) iris amber and sometimes exhibiting a faint reddish hue in adult males and yellowish in adult females; (8) body uniformly bright grass-green; (9) postocular streak narrow and white, with a few scale margins slightly tinged with yellow or reddish-brown in males, and absent in females; (10) ventrolateral stripe along the first dorsal scale row, variable in coloration in males, occurring in two forms, the first is a narrow white band bordered dorsally by a faint yellowish margin and ventrally by a red line, with a diffuse brownish tinge below the red line; the second is a narrow white band bordered by faint yellowish margins; and in females, the stripe is absent or reduced, and almost entirely white when present; (11) the ventral surfaces pale yellowish white or pale greenish-yellow anteriorly; gradually transitioning to greenish-yellow or light green toward the posterior body; (12) tail distinctly bicolored dorsally, green anteriorly and becoming almost uniformly orange or light orange-red posteriorly.

Etymology.

The specific epithet loong is a Latinized appositive noun derived from the Chinese word “龙” ( lóng), meaning “ loong ” or “dragon.” In Chinese culture, snakes are often regarded as “little dragons” or “lesser dragons” because of their serpentine form and symbolic association with the dragon ( loong ). The name also refers to the type locality, Qinglongxia (青龙峡), which literally translates to “Green Dragon Gorge.” The vivid green coloration of the new species echoes this name, establishing both symbolic and geographical connections. In addition, the year 2025, which marks the discovery and collection of this species, corresponds to the Year of the Snake in the lunar calendar. We therefore propose the common names “昆明竹叶青蛇” (Kūn Míng Zhu ́ Ye ̀ Qīng She ́) in Chinese and “Kunming Green Pit Viper” in English, referring to its type locality Kunming City, Yunnan Province, China.

Description of holotype.

(Fig. 3 ) Morphology. Adult male in a good state of preservation. Body cylindrical and elongated, with SVL 517 mm, TAL 129 mm, and TL 646 mm; tail relatively long, TAL / TL ratio 0.20; head triangular, wide at base, clearly distinct from the neck, HL 25.8 mm, HW 17.7 mm, HH 9.8 mm, HW / HL ratio 0.69. Snout elongate, round anteriorly, ESD 8.6 mm, EN 5.4 mm, ESD / HL ratio 0.33. Eyes of moderate size, ED 3.3 mm, ED / ESD ratio 0.38, and ED / HL ratio 0.13; pupil is vertically elliptical, becoming progressively narrower in brighter light and widening in dimmer conditions in live individual.

Head scalation. Rostral triangular, slightly visible from above; nasal single, undivided, completely separated from the first supralabial; nostril positioned centrally within the nasal scale; a pair of slightly enlarged internasals, separated from each other by two small anterior scales and one larger posterior scale; 3 / 4 canthal scales bordering the canthus rostralis between the internasal and corresponding supraocular. Loreal pit present, triangular in shape, located closer to eye than to nostril. PRO 3 / 3, elongate, two upper preoculars positioned above the loreal pit, both in contact with the single loreal, the lower preocular forms the lower margin of the loreal pit and contacts the 3 rd supralabial; PO 2 / 2; SBO 1 / 1, long and crescent-like, contacting the 3 rd supralabial, separated from the 4 th – 6 th supralabial by two row of scales; SO 1 / 1, large, SOL 4.3 mm, SOW 1.9 mm. Scales on the dorsal surface of the snout enlarged, flat, smooth, and irregular in shape, gradually decreasing in size posteriorly; cephalic scales small, smooth, and irregularly shaped; IOS 9; temporal scales smooth and occipital scales very weakly keeled. SL 10 / 10, the 1 st supralabial triangular; the 2 nd is the tallest, with a concave upper part forming the anterior border of the loreal pit, completely separated from the nasal by two small scales; the 3 rd widest, with the remaining supralabials gradually decreasing in size posteriorly; IL 12 / 11, the first pair in contact with each other behind the mental; the first two pairs in contact with the single pair of chin shields.

Body scalation. DSR 19-19 - 15; at midbody, all dorsal scale rows except the outermost are weakly keeled, with keels faint laterally and becoming more distinct toward the mid-dorsal rows. The outermost row is completely smooth. VS 150 (+ 2 preventrals); SC 67, paired; CP entire.

Hemipenis (Fig. 4 ). Described based on the everted left organ. When fully everted, the hemipenis is relatively short and robust, extending to the 11 th subcaudal scale. Total length ( HTL) 27.4 mm; total width ( HTW) 12.9 mm. It is Y-shaped and bilaterally symmetrical, with truncus length ( HCL) 18.0 mm, HCL / HTL ratio 0.66.

The basal one-fifth of the truncus is smooth. Above this region, a sparse ring of fine spines appears. These small spinules extend upward along the outer margin of the sulcus spermaticus, gradually increasing in size to form a row of slightly larger keratinized spines, which disappear halfway along the bifurcated region. These spines are arranged in a nearly symmetrical pattern on both sides, with 14 well-developed keratinized spines on the left and 18 on the right (excluding the smaller spines along the margin of the sulcus spermaticus). On the sulcate side, the area medial to the sulcus spermaticus corresponds to the calyx region, while the lateral area constitutes the spine region. On the asulcate side, the boundary between the spine and calyx regions is oblique and clearly demarcated; the calyculate region is restricted to the distal half of each branch. The sulcus spermaticus is divided and runs centrifugally, extending nearly to the tip of each branch. It bifurcates at a distance of 8.8 mm from the bottom of the hemipenis, with an SPBD / HCL ratio of 0.49. The sulcal lips are well developed but not prominently raised, and lack spinules.

Coloration of holotype in life (Fig. 5 ). The dorsal surface of the head and body is bright and grass-green, lacking crossbars or mottling, with a slightly paler tone along the sides that deepens toward the middle. The interstitial skin between the dorsal scales is relatively uniformly dark grayish-black or black, visible only when the body is inflated. A narrow postocular stripe, white with a faint yellowish margin, extends posteriorly from below the loreal pit, passes beneath the eye, and ultimately merges with a distinct, continuous ventrolateral stripe that runs along the first dorsal scale row from just behind the corner of the mouth to the cloacal plate, and continues as a broken line onto the anterior part of the tail. The ventrolateral stripe consists of a narrow white line occupying the center of the first dorsal scale row, bordered dorsally by a faint yellowish edge, and ventrally by a thin, red line, with a diffuse brownish tinge below the red line and the upper and lower margins of the scales remaining green.

The dorsal scales immediately above the stripe are bright green with fine creamish-blue speckling. The dorsal surface of the tail is distinctly bicolored, green in the anterior half and gradually suffused with nearly uniform light orange-red toward the distal half, with the tail tip blackish brown (Fig. 6 A ). The infralabials are light green, transitioning to light yellowish white toward the ventral surface of the head. On the anterior portion of the venter, the lateral edges are yellowish-green, while the center is creamish-yellow. Posterior to the midbody, the ventral surface becomes more uniformly light green or yellowish-green. The anterior portion of the ventral surface of the tail is pale green, while the posterior portion is orange-red. The iris is amber with a faint, almost imperceptible reddish tint and a subtle golden hue.

Coloration of the holotype in preservative. As the holotype had been preserved in alcohol for less than one month at the time of description, its coloration had not undergone any substantial change. Minor alterations were observed only in certain regions: the eyes turned pale gray, several lateral rows of dorsal scales had turned dull yellowish-green, and the small bluish-white speckles had gradually disappeared. The yellow upper margin of the ventrolateral stripe has disappeared, the central red line has become dull, and the stripe has changed to white with reddish-brown. The ventral surface of the head had gradually become pale creamish-yellow; the pale yellowish-green coloration along the lateral margins of the anterior ventral body had faded; and the central yellowish-white region had become even paler.

Variation.

The main morphological characters of Trimeresurus loong sp. nov. are listed in Table 4 . The longest known male specimen is 748 mm long ( QHU R 2025028 ( paratype); SVL 516 mm, TAL 117 mm); and the only known female specimen with is 792 mm long ( QHU R 2025031 ( paratype); SVL 657 mm, TAL 135 mm); TAL / TL ratio 0.19–0.20 in males, and 0.17–0.19 in females.

Scalation (Fig. 7 ). Nasal single, undivided; internasals slightly enlarged, separated by either juxtaposed scales, or by a combination of two small anterior scales and one larger posterior scale; SO usually 1 / 1, but in specimen QHU R 2025028 the left supraocular is divided into three small scales and the right into two; temporal scales smooth; occipital scales are mostly weakly keeled, but smooth in specimens QHU R 2025028 and QHU R 2025032 ; IOS 7–11; PRO 3; PO 2–4; SL 10–11; IL 11–14. DSR (19–23) - 19-15; at midbody, all dorsal scale rows except the outermost are weakly keeled, with keels faint laterally and becoming more distinct toward the mid-dorsal rows. The outermost row is completely smooth. VS 150–151 in males and 157–158 in females; SC 67–68 in males and 57–64 in females, paired; CP entire.

Main characters of hemipenis (Fig. 4 A, B ). The description is based on the everted organ of two male specimens ( QHU R 2025027 and QHU R 2025028 ). When fully everted, the hemipenis is relatively short and robust, extending to the 10 th – 11 th subcaudal scale. The hemipenis is Y-shaped and bilaterally symmetrical, the truncus is slightly longer than the branches, with HCL / HTL ratio 0.62–0.66.

The basal one-fifth of the truncus is smooth. Above this region, a sparse ring of fine spines appears. These small spinules extend upward along the outer margin of the sulcus spermaticus, gradually increasing in size to form a row of slightly larger keratinized spines, which disappear halfway along the bifurcated region. These spines are arranged in a nearly symmetrical pattern, with 14–19 conspicuously enlarged spines of varying sizes on each side (excluding the smaller spines along the margin of the sulcus spermaticus). On the sulcate side, the area medial to the sulcus spermaticus corresponds to the calyx region, while the lateral area constitutes the spine region. On the asulcate side, the boundary between the spine and calyx regions is oblique and clearly demarcated; the calyculate region is restricted to the distal half of each branch. The sulcus spermaticus is divided and runs centrifugally, bifurcating near the midpoint of the truncus and extending nearly to the tip of each branch, with SPBD / HCL ratio of 0.43–0.49. The sulcal lips are well-developed but not prominently raised, and lack spinules.

Main characters of the pattern in life (Fig. 8 ). Coloration in life shows moderate variation among males, while only limited information is available for females due to the small sample size. This species exhibits sexual dichromatism. In males, the eyes are amber in color. Among the two adult specimens ( QHU R 2025027 and QHU R 2025028 ), the irises exhibit a slight reddish hue, whereas in the two subadult specimens ( QHU R 2025029 and QHU R 2025030 ), the eyes are purely amber. The postocular streak is narrow and white, with a few scale margins slightly tinged with yellow or reddish-brown. The ventrolateral stripe runs along the first dorsal scale row and is variable in coloration among males, occurring in two forms. In most male specimens, it consists of a narrow white band bordered dorsally by a faint yellowish margin and ventrally by a thin, red line, with a diffuse brownish tinge below the red line. However, in QHU R 2025028 , the ventrolateral stripe is only a narrow white band bordered on both sides by faint yellowish margins. In some individuals, the upper and lower margins of the first dorsal scale row remain green.

In females, the eyes are yellowish. The postocular streak is absent in both specimens. The ventrolateral stripe is absent in QHU R 2025032 , while in QHU R 2025031 it is narrow, white, and restricted to the middle portion of the first dorsal scale row.

In all individuals, the dorsal surfaces of the head and body are grass green. In males, the lateral body coloration is slightly paler than the mid-dorsal region, and the lateral dorsal scales are variably speckled with fine creamish-blue or white spots. In contrast, females exhibit a uniformly grass-green coloration across the entire dorsum. The dorsal surface of the tail is distinctly bicolored: green anteriorly, gradually transitioning to nearly uniform orange or light orange-red posteriorly, with the tail tip being blackish brown (Fig. 6 B – E ). The ventral surface of the head and the central portion of the anterior ventral body are noticeably paler, appearing pale whitish-green or creamish-yellow. Posterior to midbody, the ventral coloration becomes uniformly yellowish-green or light green. The anterior portion of ventral surface of the tail is pale green, while the posterior portion is light orange-red.

Main characters of the pattern in preservative. The description is based on a subadult male specimen ( QHU R 2025029 ) and a female specimen ( QHU R 2025032 ), both collected in May 2025. After approximately five months in alcohol, the dorsal surface of the head had turned olive-yellow and that of the body yellow in both specimens. The eyes had become pale gray, and the supralabials as well as the ventral surface of the head had faded to milky white. The lateral portions of the ventral body were pale yellow, while the entire central ventral surface had turned creamish-yellow. In the male specimen, the posterior portion of the ventral body was slightly yellowish-green. The orange-red area of the tail remained relatively well defined. In the male specimen, the ventrolateral stripe had changed to white dorsally and brownish with a slight reddish hue ventrally.

Distribution and natural history.

Currently, Trimeresurus loong sp. nov. is certainly known only from the type locality, Qinglongxia, Anning City, Kunming City, Yunnan Province, China, at an elevation of approximately 1,822 m asl. All specimens were encountered during the first half of the night, coiled within shrubs on hillsides near streams in well-preserved broad-leaved forest (Fig. 10 A – C ), when nighttime temperatures ranged 15 ° C ~ 18 ° C. The female specimen QHU R 2025031 defecated immediately when disturbed during capture. Its feces contained numerous bird feathers, suggesting that small birds may constitute part of the adult diet of this species (Fig. 10 D ).

Comparisons.

Trimeresurus loong sp. nov. is assigned to the subgenus Viridovipera based on a combination of diagnostic characters, including its phylogenetic position, the complete separation of the first supralabial from the nasal scale, and a short spinose hemipenis, all of which are characteristic features of Viridovipera (e. g., Nguyen et al. 2025; Xu et al. 2025). Accordingly, morphological comparisons are restricted to congeners within Viridovipera , which currently comprises nine recognized species and represents the most relevant group for differential diagnosis. The principal characters distinguishing Trimeresurus loong sp. nov. from these congeners are summarized in Table 5 and illustrated in Fig. 10 .

Morphologically, Trimeresurus loong sp. nov. is most similar to T. yunnanensis (distributed in central to southwestern Yunnan Province of China, the Mandalay Region and Shan State of Myanmar, northern Laos, northern and central Thailand, and northern to central Vietnam), but it can be clearly distinguished from the latter by the following combination of characters: (1) smaller maximum SVL in females ( 657 mm vs. 804 mm); (2) lower total number of VS + SC in males (217–219 [mean 217.5 ± 1.0] vs. 221–231 [mean 225.9 ± 3.9]); (3) irises amber in males vs. bright or deep red irises observed in males of T. yunnanensis (Fig. 10 A, B, K ); (4) the ventrolateral stripe in the males of the new species is slender and limited to the first dorsal scale row occurring in two forms, either a narrow white band bordered dorsally by a faint yellowish margin and ventrally by a red line with a diffuse brownish tinge below the red line, or a narrow white band bordered by faint yellowish margins on both sides, while in the males of T. yunnanensis the stripe is broader and more vivid, occupying the entire first dorsal scale row and the lower margin of the second row, even extending onto the lateral edges of the ventrals, consisting of a thick red lower border and a white upper zone with sharply separated colors visible from a distance; (5) the new species has a anteriorly green coloration of tail, posteriorly gradually transitioning to a uniformly orange or light orange-red. In contrast, T. yunnanensis shows dark red blotches forming large, irregular patches with uneven margins on the anterior part of the tail (Fig. 11 ). In hemipenial morphology, Trimeresurus loong sp. nov. can be distinguished from T. yunnanensis by longer hemipenial truncus and a shorter degree of bifurcation ( HCL / HTL ratio 0.62–0.66 vs. 0.69), a more distal sulcus spermaticus bifurcation point ( SPBD / HCL ratio 0.43–0.49 vs. 0.30), and a greater number of enlarged spines (14–19 per side vs. 9–10, excluding the smaller spines lining the margin of the sulcus spermaticus) (Fig. 4 A, B, F ).

Trimeresurus loong sp. nov. differs from T. mayaae (distributed across the Indian States of Manipur, Meghalaya, Mizoram, Assam, Nagaland, West Bengal, Sikkim, Bhutan, and Chin State of Myanmar) by the following combination of characters: larger maximum SVL in females ( 657 mm vs. 590 mm); lower number of VS in males (150–151 [mean 150.3 ± 0.5] vs. 153–163 [mean 158.1 ± 3.0]); higher number of SC in females (57–64 [mean 60.5 ± 4.9] vs. 53–55 [mean 54.0 ± 1.0]); and higher number of VS + SC in females (215–221 [mean 218.0 ± 4.2] vs. 205–208 [mean 206.7 ± 1.5]). In addition, females of Trimeresurus loong sp. nov. have yellowish irises, distinctly differing from the greenish eyes of T. mayaae .

Trimeresurus loong sp. nov. differs from T. medoensis (distributed in the Xizang AR of southwestern China, and possibly in northern Myanmar and northeastern India) by the following combination of characters: slight larger maximum SVL in both sexes ( 601 mm in males, 657 mm in females vs. 553 mm in males, 624 mm in females); higher number of VS in both sexes (150–151 [mean 150.3 ± 0.5] in males, 157–158 [mean 157.5 ± 0.7] in females vs. 146–151 [mean 148.6 ± 1.8] in males, 145–147 [mean 146.0 ± 1.0] in females); greater number of SC in males (67–68 [mean 67.3 ± 0.5] vs. 55–59 [mean 57.0 ± 1.4]); and higher number of VS + SC in both sexes (217–219 [mean 217.5 ± 1.0] in males, 215–221 [mean 218.0 ± 4.2] in females vs. 201–208 [mean 205.6 ± 2.9] in males, 204–206 [mean 205.0 ± 1.0] in females). The new species also possesses a greater number of SL (10–11 vs. 8–9) and IL (11–14 vs. 8–10). It further differs in having more dorsal scale rows at midbody (19 vs. 17) and posteriorly (15 vs. 13, rarely 11). Eye coloration also differs: males of new species have amber irises with a slight reddish hue, and females yellowish, whereas both sexes of T. medoensis possess green or yellowish-green eyes (Fig. 10 A, B, E ). In addition, the ventrolateral stripe in females of new species is absent or uniformly white, contrasting with the red-and-white stripe of T. medoensis . In hemipenial morphology, Trimeresurus loong sp. nov. can be distinguished from T. medoensis by longer hemipenial truncus and a higher degree of bifurcation ( HCL / HTL ratio 0.62–0.66 vs. 0.53), and a more distal sulcus spermaticus bifurcation point ( SPBD / HCL ratio 0.43–0.49 vs. 0.21) (Fig. 4 A – C ).

Trimeresurus loong sp. nov. differs from T. nujiang (distributed across several localities within the Nujiang River Basin of northwestern Yunnan Province, China, including Gongshan, Fugong, and Lushui Conties) by the following combination of characters: slightly smaller maximum SVL in both sexes ( 601 mm in males, 657 mm in females vs. 694 mm in males, 682 mm in females); lower number of VS in both sexes (150–151 [mean 150.3 ± 0.5] in males, 157–158 [mean 157.5 ± 0.7] in females vs. 164–173 [mean 168.7 ± 3.6] in males, 165–168 [mean 166.6 ± 1.3] in females); and lower number of VS + SC in both sexes (217–219 [mean 217.5 ± 1.0] in males, 215–221 [mean 218.0 ± 4.2] in females vs. 226–241 [mean 231.3 ± 6.8] in males, 222–226 [mean 224.8 ± 1.8] in females). Eye coloration also differs, with males of the new species having amber irises with a slight reddish hue vs. yellow or mottled gray and flesh-colored in T. nujiang (Fig. 10 A, B, F ). In addition, a postocular streak is present in males of new species but absent or very faint in T. nujiang .

Trimeresurus loong sp. nov. differs from T. pretiosus (distributed in Yadong County, Xigaze City, Xizang AR, China) by the following combination of characters: having a larger maximum SVL in both sexes ( 601 mm in males, 657 mm in females vs. 516 mm in males, 512 mm in females); a higher number of VS (150–151 [mean 150.3 ± 0.5] in males, 157–158 [mean 157.5 ± 0.7] in females vs. 140–143 [mean 141.5 ± 2.1] in males, 142 in female); a greater number of SC (67–68 [mean 67.3 ± 0.5] in males, 57–64 [mean 60.5 ± 4.9] in females vs. 56–58 [mean 57.0 ± 1.4] in males, 54 in female); a higher number of VS + SC (217–219 [mean 217.5 ± 1.0] in males, 215–221 [mean 218.0 ± 4.2] in females vs. 198–199 [mean 198.5 ± 0.7] in males, 196 in female); a greater number of supralabials (10 or 11 vs. 8 or 9); in possessing all subcaudal scales paired (vs. partly single); and eye coloration in males is amber with a slight reddish hue (vs. brick red) (Fig. 10 A, B, G ). In hemipenial morphology, Trimeresurus loong sp. nov. can be distinguished from T. pretiosus by longer hemipenial truncus and a lower degree of bifurcation ( HCL / HTL ratio 0.62–0.66 vs. 0.47–0.53), and a more distal sulcus spermaticus bifurcation point ( SPBD / HCL ratio 0.43–0.49 vs. 0.28–0.36) (Fig. 4 A, B, D ).

Trimeresurus loong sp. nov. differs from T. stejnegeri (restricted to eastern and southern China, including Taiwan Province, northern Vietnam, and northeastern Laos) by the following combination of characters: lower VS in males (150–151 [mean 150.3 ± 0.5] vs. 154–178 [mean 164.5 ± 4.8]); lower number of VS + SC in males (217–219 [mean 217.5 ± 1.0] vs. 218–256 [mean 234.9 ± 7.7]); and fewer dorsal scale rows at midbody (19 vs. 21–23). In males, the irises are amber with a slight reddish hue, and the ventrolateral stripe is slender and confined to the first dorsal scale row, occurring in two forms: either a narrow white band bordered dorsally by a faint yellowish margin and ventrally by a red line with a diffuse brownish tinge below the red line, or a narrow white band bordered by faint yellowish margins on both sides in Trimeresurus loong sp. nov. In contrast, in T. stejnegeri , the irises are orange-red or red (Fig. 10 A, B, H ), and the ventrolateral stripe consists of a red lower border and a white upper zone, with the two colors sharply separated and clearly visible from a distance. In females, the ventrolateral stripe is uniformly white, whereas in T. stejnegeri it is white or red-and-white. In hemipenial morphology, Trimeresurus loong sp. nov. can be distinguished from T. stejnegeri by shorter hemipenial truncus and a higher degree of bifurcation ( HCL / HTL ratio 0.62–0.66 vs. 0.69), and a more distal sulcus spermaticus bifurcation point ( SPBD / HCL ratio 0.43–0.49 vs. 0.28) (Fig. 4 A, B, E ).

Trimeresurus loong sp. nov. differs from T. truongsonensis (restricted to central Vietnam and central Laos) by the following combination of characters: a larger maximum SVL in both sexes ( 601 mm in males, 657 mm in females vs. 521 mm in males, 488 mm in females); a lower number VS (150–151 [mean 150.3 ± 0.5] in males, 157–158 [mean 157.5 ± 0.7] in females vs. 170–190 [mean 179.8 ± 8.7] in males, 165–167 [mean 166.0 ± 1.0] in females); a greater number of SC (67–68 [mean 67.3 ± 0.5] in males, 57–64 [mean 60.5 ± 4.9] in females vs. 56–58 [mean 57.0 ± 1.4] in males, 54 in the female); and consequently a lower number of VS + SC (217–219 [mean 217.5 ± 1.0] in males, 215–221 [mean 218.0 ± 4.2] in females vs. 235–259 [mean 247.2 ± 10.7] in males, 228–235 [mean 232.7 ± 4.0] in females); and fewer dorsal scale rows at midbody ( MSR 19 vs. 21). Eye coloration is amber with a slight reddish hue in males and yellowish in females, contrasting with the greenish-yellow eyes of both sexes in the latter species (Fig. 10 A, B, I ). The body is uniformly bright grass-green, whereas T. truongsonensis exhibits a greenish-blue dorsum with broad brown crossbands.

Finally, Trimeresurus loong sp. nov. differs from T. vogeli (distributed in the southeastern part of central Thailand, central and southern Laos, Cambodia, and central and southern Vietnam) by the following combination of characters: smaller maximum SVL in both sexes ( 601 mm in males, 657 mm in females vs. 661 mm in males, 947 mm in females); lower number of VS in males (150–151 [mean 150.3 ± 0.5] vs. 157–169 [mean 162.8 ± 3.7]); lower number of VS + SC in males (217–219 [mean 217.5 ± 1.0] vs. 221–238 [mean 229.8 ± 4.9]); fewer dorsal scale rows at midbody ( MSR 19 vs. 21, rarely 20); and eye coloration in males is amber with a slight reddish hue (vs. light orange or flesh-colored) (Fig. 10 A, B, J ).

Figures

Figure 3. Fresh specimen of the holotype of Trimeresurus loong sp. nov. (QHU R 2025027, adult male). Photographs by Y. H. Xu. Scale bars: 10 mm.

Figure 4. Comparisons of hemipenes within the subgenus Viridovipera, showing morphological differences on sulcus side, asulcate side, and apical side of hemipenis, from left to right. A. Trimeresurus loong sp. nov., QHU R 2025027, holotype; B. Trimeresurus loong sp. nov., QHU R 2025028, paratype; C. T. medoensis, QHU R 2025040, from Motuo (Medog), Xizang, China; D. T. pretiosus, QHU R 2025020, from Yadong, Xizang, China; E. T. stejnegeri, QHU R 2025037, from Lishui, Zhejiang, China; F. T. yunnanensis, QHU R 2025035, from Lincang, Yunnan, China. SPBP: sulcus spermaticus bifurcation point. Photographs by Y. H. Xu. Scale bars: 10 mm.

Figure 5. Coloration of the holotype of Trimeresurus loong sp. nov. in life (QHU R 2025027, adult male). A. Dorsolateral view; B. Ventral view; C. Dorsal view of the head; D. Lateral view of the head; E. Ventral view of the head; F. Lateral view of the body; G. Ventral view of the body. Photographs by Y. H. Xu.

Figure 6. Dorsal and ventral views of the tail of Trimeresurus loong sp. nov. A. QHU R 2025027, holotype, adult male; B. QHU R 2025028, paratype, adult male; C. QHU R 2025029, paratype, subadult male; D. QHU R 2025030, paratype, subadult male; E. QHU R 2025031, paratype, adult female. Photographs by Y. H. Xu. Scale bars: 20 mm.

Figure 7. Paratypes of Trimeresurus loong sp. nov. A. Dorsal view of the head; B. Lateral view of the head; C. Ventral view of the head; D. Lateral view of the body; E. Ventral view of the body. A 1 – E 1. QHU R 2025028, adult male; A 2 – E 2. QHU R 2025029, subadult male; A 3 – E 3. QHU R 2025030, subadult male; A 4 – E 4. QHU R 2025031, adult female; A 5 – E 5. QHU R 2025032, adult female. Photographs by Y. H. Xu.

Figure 8. Coloration of the paratypes of Trimeresurus loong sp. nov. in life. A. Lateral view of the head; B. Dorsolateral view; C. Ventral view. A 1 – C 1. QHU R 2025028, adult male; A 2 – C 2. QHU R 2025029, subadult male; A 3 – C 3. QHU R 2025030, subadult male; A 4 – C 4. QHU R 2025031, adult female. Photographs by Y. H. Xu.

Figure 9. Habitat and field observations of Trimeresurus loong sp. nov. A. The microhabitat of the new species in Anning, Kunming, China; B. Holotype QHU R 2025027 in life, in situ; C. Paratype QHU R 2025028 in life, in situ; D. Feces of the paratype QHU R 2025031. Photographs by Y. H. Xu (A – C) and J. D. Deng (D).

Figure 10. Comparison of the lateral head view of males of species in the subgenus Viridovipera in life. A. Trimeresurus loong sp. nov., QHU R 2025027, holotype; B. Trimeresurus loong sp. nov., QHU R 2025028, paratype; C. Trimeresurus sp. from Chengdu, Sichuan, China; D. T. mayaae from Kangpokpi, Manipur, India; E. T. medoensis, QHU R 2025040, from Motuo (Medog), Xizang, China; F. T. nujiang from Gongshan, Yunnan, China; G. T. pretiosus, QHU R 2025020, from Yadong, Xizang AR, China; H. T. stejnegeri, QHU R 2025037, from Lishui, Zhejiang, China; I. T. truongsonensis from Phong Nha-Ke Bang NP, Quang Tri, Vietnam; J. T. vogeli from Phong Nha-Ke Bang NP, Quang Tri, Vietnam; K. T. yunnanensis from Jingdong, Yunnan, China; L. T. cf. yunnanensis from Mt. Dawei, Honghe, Yunnan, China. Photographs by Y. H. Xu (A – C, E – L) and P. Shinde (D).

Figure 11. Comparison of male coloration between Trimeresurus loong sp. nov. and T. yunnanensis. A 1. Trimeresurus loong sp. nov., QHU R 2025028; A 2. Trimeresurus loong sp. nov., QHU R 2025029; B 1. T. yunnanensis, QHU R 2025035, from Lincang, Yunnan, China; B 2. T. yunnanensis, unvouchered individual from Jingdong, Yunnan, China. The white arrows indicate the dorsal surface of the tail, and blue arrows indicate the ventrolateral stripe. Photographs by Y. H. Xu.