Holotype.BMNH 1932.5.1.2, adult female, collected from China (discussion for the exact locality see Remarks below).

Seven adult males and three adult females. Males CIB 44475–44476, from Guangzhou, Guangdong Province, China; male SYS a000534, from Mt Danxia (25.0347 N, 113.7407 E), Renhua County, Guangdong; males SYS a008120–8121, 8123, 8125, and females SYS a008122, 8124, from Shimentai Nature Reserve (24.3818 N, 113.3927 E), Yingde City, Guangdong; female SYS a000488, from Mt Luoyang, Lingshan County, Guangxi Zhuang Autonomous Region, China.

The specific name obscura means ‘obscure’ in Latin.

“Chinese floating frog” in English / “中国浮蛙 (zhōng guó fú wā)” in Chinese.

(1) Body stocky, size small, SVL 24.2–27.5 mm in adult males (n=7) and 31.5–32.2 mm in adult females (n=3); (2) snout short triangular shaped; (3) nostrils located dorsally; (4) eye orientation vertically; (5) loreal region oblique, not concave or convex; (6) interorbital space narrower than internarial distance; (7) tongue narrow and slender, unnotched, pointed distally, lingual papilla absent; (8) vomerine ridge and vomerine teeth absent; (9) supratympanic fold distinct, raised, and granulated, curved on the temporal region; (10) tympanum hidden, edge invisible; (11) fingers with rudimentary webs, toes with full webs; (12) heels not meeting, tibio-tarsal articulation reaching between the posterior and anterior of the eye.

Occidozyga obscura comb. nov. was previously synonymized with O. lima. These two species are most similar to each other. However, Occidozyga obscura comb. nov. can be distinguished by the combination of the following characteristics: loreal region oblique, not concave or convex (vs. slightly concave in O. lima), interorbital space narrower than internarial distance (vs. subequal), supratympanic fold distinct, raised, and granulated (vs. indistinct), inner metatarsal tubercle large and raised (vs. weakly projecting), and tibio-tarsal articulation reaching between the posterior and anterior of the eye (vs. reaching tip of nostril).

Occidozyga obscura comb. nov. furthers differs from O. berbeza by the supratympanic fold curved on the temporal region (vs. straight), fingers with rudimentary webs (vs. unwebbed), and outer metatarsal tubercle present (vs. absent). O. obscura comb. nov. distinctly differs from O. rhacoda by the dorsolateral fold absent (vs. present), and fingers with rudimentary webs (vs. unwebbed).

Occidozyga obscura comb. nov. can be easily distinguished from the remaining 13 congeners O. baluensis, O. celebensis, O. diminutiva, O. floresiana, O. laevis, O. magnapustulosa, O. martensii, O. myanhessei comb. nov., O. semipalmata, O. sumatrana, O. shiwandashanensis, O. swanbornorum comb. nov., and O. tompotika, by the tongue narrow and slender (vs. wide and swollen in all of these 13 species).

Based on the examined specimens (n=10). All specimens were similar in morphology. The measurements are given in Table 3.

Body stocky, small-sized, SVL 24.2–27.5 mm (n=7) in males and 31.5–32.2 mm (n=3) in females. Head flat above, almost as wide as long (HDW/HDL 0.97–1.09, n=10); pineal ocellus absent; snout short triangular shaped, distinctly protruding beyond lower jaw, tip of snout rounded in dorsal view and profile; canthus rostralis absent, loreal region oblique, not concave or convex; nostril rounded, located dorsally, distinctly raised, closer to the tip of snout than to the eye; eye orientation vertically, pupil diamond shaped; interorbital space narrower than internarial distance; tympanum hidden, edge invisible; vomerine ridge and teeth absent; tongue narrow and slender, unnotched, pointed distally, lingual papilla absent.

Forelimbs short, lower arm 13–18% (n=10) of SVL and hand 26–32% (n=10) of SVL; fingers distinctly thin and long, relative finger lengths I<II<IV<III; tips of fingers pointed, not dilated, and without disks; distinct lateral fringes on inner and outer sides of each finger, fingers with rudimentary webs, more distinct between fingers I and II; subarticular tubercles present at the bases of each finger, prominent and rounded; supernumerary tubercles absent; inner and outer palmar tubercles prominent and rounded.

Hind limbs robust, tibia 41–47% (n=8) of SVL and foot 66–80% (n=8) of SVL; heels not meeting when hind limbs flexed at right angles to the axis of the body; tibio-tarsal articulation reaching between the posterior and anterior of the eye when hind limb is stretched along the side of the body; toes distinctly long and thin, relative lengths I<II<III<V<IV; tips of toes pointed, dilated into pear-shaped disks; toes with full webs, metatarsal web present, distinct lateral fringes on lateral edges of toes I and V; subarticular tubercles rounded, prominent; inner metatarsal tubercle large and long-elliptic, slightly raised, length twice the width; outer metatarsal tubercle relatively smaller than the inner metatarsal tubercle, distinctly raised and pointed, length slightly larger than width; inner tarsal fold relatively flat, in contact with the inner metatarsal tubercle; tarsal tubercle large and distinctly raised, close to the tibio-tarsal articulation.

Dorsal surface relatively rough, transverse wrinkles and dense tubercles on the dorsum, head, flanks, and limbs; small granules on the dorsal rears of hands and tarsi; not bearing spinules on the dorsal skin; supratympanic fold distinct, raised and granulated, extending from the posterior corner of the eye, curved on the temporal region, to the previous shoulder; dorsolateral fold absent. Ventral surface with large flattened tubercles, denser on the throat and thighs; dense granules on the ventral feet and tarsi.

In life (Fig. 3), dorsal surfaces vary from olive brown to dark brown; dorsum and flanks interspersed with irregular black speckles; mid-dorsal stripe grass-green with distinct border; lateral line system grayish brown to yellowish brown. Pupil bordered with yellow, iris beige to brown. Supratympanic fold olive-brown to dark brown. Skin of throat, chest, and belly uniform creamy white; gular with a pair of distinct or indistinct longitudinal dark stripes; skin of limbs dark gray, tubercles on ventral thighs and tibias creamy white.

In preservative (Fig. 4A, B), dorsum light gray; black speckles on dorsal surface light brown; mid-dorsal stripe fainted and the border indistinct; ventral skin grayish white; tubercles on ventral surface more distinct.

Male with a single subgular vocal sac; in breeding season, a single, light grey nuptial pad on the dorsal surface of finger I, nuptial spinules invisible. Males (SVL 24.2–27.5 mm) distinctly smaller than females (SVL 31.5–32.2 mm) (Fig. 4A, B).

This frog inhabits natural or artificial ponds and paddy fields in plain areas. They quickly dive underwater after being disturbed during the daytime, while become relatively insensitive at night. Males call in the water surface or waterside grass from dusk to dawn, more active during the rain. The breeding season is from April to August (this study; Fei et al. 2009).

Occidozyga obscura comb. nov. can be recognized from several localities of Guangdong and Guangxi, southeastern China (Figs 1, 2), based on the analyzed vouchers in this work. The previous records of O. lima from Guangdong, Guangxi, Hong Kong, Macao, and Fujian, southeastern China are reassigned to O. obscura currently (see Remarks below). The records of O. lima from Yunnan require further clarifications with molecular and morphological vouchers (which might be close to the lineage of O. cf. lima based on the biogeographical similarity).

This species was previously reported as common and widespread species in southeastern China under the nomen O. lima, but its population quantity is found rapidly declining due to the influence of human activities such as pesticide abuse and urban construction. The populations in Hong Kong, Macao, Shenzhen, Guangzhou, and Xiamen might disappear, as no more reports and vouchers in nearly 20 years (this study; Chan 2013). We recommend Occidozyga obscura comb. nov. to be listed as Endangered (EN) [IUCN Red List criteria A2cd].

The type specimen of Occidozyga obscura comb. nov. was collected by John Reeves (1774–1856) but the exact type locality was not given in the original description (Gray 1831). Zhao & Adler (1993) speculated that the type specimens may be from somewhere in southeastern China, especially Macao or Canton (= Guangzhou) in Pearl River Delta, where John Reeves lived and worked in.

Moreover, there were two historic species currently regarded as synonymies of O. lima, namely Oxyglossa lima var. chinens and Osteosternum amoyense (Stejneger 1925; Smith 1931; Pope 1931). The type locality for Oxyglossa lima var. chinens is Lilong, Canton (= Lilang, Shenzhen, Guangdong), and for Osteosternum amoyense is Amoy (= Xiamen, Fujian). During our field surveys, we are unable to observe any frogs that resembled these two historic species from Shenzhen or Xiamen, possibly due to the dramatic urbanization of these two cities. Nevertheless, according to their original descriptions and distributions, we propose to transfer these two taxa to be the synonymy of Occidozyga obscura comb. nov.

Holotype.SYS a008846, adult male, collected on 18 July 2021 by Zhi-Tong Lyu from Mt Wugongling (22.5914 N, 114.4927 E), Shenzhen City, Guangdong. Paratypes. Seven adult males and three adult females. Male SYS a008847 CIB 118529, collected at the same time as the holotype; males SYS a005589–90, collected on 15 November 2016 by Zhi-Tong Lyu and Jian Wang from Mt Wugongling; males SYS a007372–7373, and females SYS a07374–7375, collected on 5 September 2018 by Jian Wang and Hong-Hui Chen from Qi’ao Island (22.4140 N, 113.6446 E), Zhuhai City, Guangdong Province, China; female SYS a004650, collected on 14 April 2016 by Jian Wang from Mt Yunkai (22.2786 N, 111.1886 E), Xinyi City, Guangdong; males SYS a007657–7658, collected on 8 April 2019 by Jian Wang from Mt Yunkai.

Five adult males and five adult females. Male SYS a005543 and female SYS a005542, from Mt Jiaoyiling (21.1592 N, 110.3093 E), Zhanjiang City, Guangdong; female SYS a005267, from Mt. Diaoluo (18.6408 N, 109.9317 E), Lingshui Li Autonomous County, Hainan; males SYS a005436–5437, 5440–5441 and females SYS a005438–5439, 5442, from Mt Bawangling (19.0944 N, 109.0491 E), Changjiang Li Autonomous County, Hainan.

The specific name lingnanica refers to the lingnan region, a geographic area covering Guangdong, Guangxi, and Hainan in southeastern China, where this new frog species occurs in. This specific name is also dedicated to the former Lingnan University (1888–1952) that was incorporated into Sun Yat-sen University after 1953.

“Lingnan floating frog” in English / “岭南浮蛙 (lǐng nán fú wā)” in Chinese.

(1) Body stocky, size small, SVL 19.9–22.1 mm in males (n=8) and 26.8–28.8 mm in females (n=3); (2) snout short triangular shaped; (3) nostrils located laterally; (4) eye orientation laterally; (5) canthus rostralis visible, rounded; (6) loreal region vertical, not concave/convex; (7) tongue wide and swollen, unnotched, rounded distally, lingual papilla absent; (8) vomerine ridge and vomerine teeth absent; (9) supratympanic fold distinct and raised, slightly curved on the temporal region; (10) tympanum hidden, edge invisible; (11) relative finger lengths II=I<IV<III, relative toe lengths I<II<V<III<IV; (12) fingers without webs, toes with two third webs; (13) heels not meeting, tibio-tarsal articulation reaching at the posterior margin of supratympanic fold; (14) tarsal fold absent.

Occidozyga lingnanica sp. nov. has been long-term misidentified as O. martensii, however, it differs from the latter by a combination of the following morphological characters: tympanum hidden, edge invisible (vs. tympanum edge raised), relative finger lengths II=I<IV (vs. II=IV<I), relative toe lengths V<III (vs. III<V), tarsal fold absent (vs. present), tibio-tarsal articulation reaching the posterior margin of supratympanic fold (vs. reaching the region of eye).

Occidozyga lingnanica sp. nov. can be distinguished from the remaining three known congeners in Clade VIII (Fig. 1) by the canthus rostralis rounded (vs. absent in O. magnapustulosa), loreal region oblique, not concave or convex (vs. slight convex in O. magnapustulosa and O. swanbornorum comb. nov.), relative finger lengths II=I<IV (vs. II<IV<I in O. myanhessei comb. nov., IV<II<I in O. swanbornorum comb. nov.), tarsal fold absent (vs. present in O. magnapustulosa and O. myanhessei comb. nov.).

For the remaining 13 congeners, Occidozyga lingnanica sp. nov. distinctly differs from O. lima, O. obscura comb. nov., and O. berbeza by the tongue wide and swollen (vs. narrow and slender); from O. rhacoda by the dorsolateral fold absent (vs. present); from O. shiwandashanensis by the tarsal fold absent (vs. present); from O. celebensis, O. laevis, and O. sumatrana by the eye orientation laterally (vs. vertically); from O. baluensis, O. floresiana, and O. semipalmata by the canthus rostralis rounded (vs. absent); from O. diminutiva and O. tompotika by the supratympanic fold curved (vs. straight).

SYS a008846, adult male (Fig. 5). Body stocky, small-sized, SVL 21.4 mm. Head longer than wide (HDW/HDL 0.97), plat above; pineal ocellus distinct; snout short triangular shaped, distinctly protruding beyond lower jaw, tip of snout rounded in dorsal view and profile; canthus rostralis rounded, loreal region oblique, not concave or convex; nostril rounded, laterally, not raised, at the middle between tip of snout and eye; eye orientation laterally, pupil diamond shaped; interorbital space distinctly narrower than internarial distance; tympanum hidden, edge invisible; vomerine ridge and teeth absent; tongue wide and swollen, unnotched, rounded distally, lingual papilla absent.

Forelimbs short, lower arm 15% of SVL and hand 25% of SVL; fingers relatively thin and long, relative finger lengths II=I<IV<III; tips of fingers rounded, not dilated and without disks; fingers without webs and fringes; subarticular tubercles present at the bases of each finger, prominent and rounded; supernumerary tubercles absent; inner and outer palmar tubercles prominent and rounded.

Hind limbs robust, tibia 44% of SVL and foot 63% of SVL; heels not meeting when hind limbs flexed at right angles to the axis of the body; tibio-tarsal articulation reaching at the posterior margin of supratympanic fold when hind limb is stretched along the side of the body; toes distinctly long and thin, relative lengths I < II < V < III < IV; tips of toes rounded, dilated into rounded disks; toes with two third webs, metatarsal web present, distinct lateral fringes on lateral edges of toes I and V; subarticular tubercles rounded, prominent; inner metatarsal tubercle large and long-elliptic, distinctly raised, length triple the width; outer metatarsal tubercle absent; tarsal fold absent.

Dorsal surface relatively rough, large tubercles scattering on skin of dorsum, flanks, and dorsal limbs, not bearing spinules on the dorsal skin; a faint fold across head between orbits; supratympanic fold distinct, raised, extending from the posterior corner of the eye, slightly curved on the temporal region, to the previous shoulder; dorsolateral fold absent. Ventral surface with large flattened tubercles; a fold across breast; dense granules on the ventral tarsi.

In life (Fig. 5), dorsal surface grayish brown with irregular black speckles; dorsal limbs with dark brown transverse bars; mid-dorsal stripe yellowish brown but indistinct; a narrow transverse bar between orbits; supratympanic fold dark brown. Pupil bordered with yellow; iris brown with irregular dark or light speckles. Skin of throat dark with white mottling; skin of chest and belly uniform creamy white; ventral surface of limbs grayish pink with dark speckles. Nuptial pad light yellow, slightly transparent.

In preservative, dorsum light gray; black speckles on dorsum and transverse bars on limbs light brown; mid-dorsal stripe grayish white and more distinct; nuptial pad light gray, slightly transparent; ventral surface grayish white; mottling on throat gray white.

The measurements of the type series are given in Table 4. All individuals were similar in morphology. Dorsal coloration varies in life, from light brown, yellowish brown, to dark brown (Figs 5, 6); mid-dorsal stripe varies among individuals, distinct (Figs 4C, 6C), indistinct (Fig. 5), or absent (Figs 4D, 6A, B, D–F); an irregular orange marking on the occipital region in some individuals (Fig. 6F).

Male with a single subgular vocal sac; in breeding season, a single, light yellow, swollen, and granular nuptial pad on the dorsal surface of finger I, nuptial spinules invisible. Males (SVL 19.9–22.1 mm) distinctly smaller than females (SVL 26.8–28.8 mm) (Fig. 4C, D).

This frog inhabits natural or artificial ponds and paddy fields in hilly regions. Males call in the water surface or waterside grass from dusk to dawn. The breeding season is from May to August (this study; Fei et al. 2009). In southeastern China, Occidozyga lingnanica sp. nov. shares a similar environment to that of Occidozyga obscura comb. nov., but prefers to hilly regions compared with the latter in plain areas.

Occidozyga lingnanica sp. nov. can be recognized from multiple localities in Guangdong and Hainan of southeastern China based on the phylogenetic result in this work (Figs 1, 2). The records of O. martensi from Yunnan, southwestern China require further clarifications with morphological examinations (see Discussion).

Occidozyga lingnanica sp. nov. was previously reported as common and widespread species in southeastern China under the nomen O. martensii. Nevertheless, during our repeated surveys throughout southeastern China, the population quantity of this species is found rapidly declining due to the influence of human activities such as pesticide abuse and urban construction. We recommend Occidozyga lingnanica sp. nov. to be listed as Vulnerable (VU) [IUCN Red List criteria B1b(ii)(iii)].