[taxon-name: Synersaga] is characterized by the forewing characters: forewing slightly broader distally with round apex, evenly colored, with yellowish brown or blackish ground color; venation with R₃ free or connate with R₄₊₅; M₃ and CuA₂ short-stalked or connate. However, the forewing color patterns of the known species are very similar to each other and they can be differentiated from one another by the shape of the uncus and the caudal processes of the juxta in the male genitalia. The abdominal tergites are densely spinose, and the seventh tergite is uniquely specialized, produced laterally with a sclerotized anterior margin.

[taxon-name: Synersaga bleszynskii] (Gozmány, 1978: 143) China

TL (Type locality): Chekiang, China. Type in HMNH.

Fig.: ^{Gozmány (1978}, Taf. 8, 37, Fig. 86; Park (2000, Figs 20, 20a)

[taxon-name: Synersaga caradjai] (Gozmány, 1978: 143) Taiwan

TL: Kosempo, Taiwan. Type in HNHM.

Fig.: ^{Gozmány (1978}, Taf. 8, 37, Fig. 85)

[taxon-name: Synersaga kuni] Park, 2007: 206 Vietnam

TL: Cuc Phoung, N. Vietnam. Type in KNA.

Fig.: ^{Park et al. (2007}, Figs 8, 17, 17a)

[taxon-name: Synersaga mondulkiriensis] sp. n. Cambodia

TL: Mondulkiri, Cambodia. Type in UIK.

Fig.: Park & Bae (2012, Figs 4–12 )

[taxon-name: Synersaga nigriptera] Park, 2007: 208 Vietnam

TL: Babe, N. Vietnam. Type in KNA.

Fig.: ^{Park et al. (2007}, Figs 9, 18, 18a, 22)

[taxon-name: Synersaga phuruaensis] Park, 2009:2 Thailand

TL: Loei, China. Type in OPU.

Fig.: ^{Park (2009}, Figs 4-6, 8, 8a, 10)

[taxon-name: Synersaga pseudocathra] (Diakonoff, 1951: 76)^* Myanmar

Ark. Zool. 1951, 3: 76. TL: Kambaiti, Myanmar. Type in NRS.

Fig.: ^{Diakonoff (1951}, Figs 13 (male), 15 &16 (female))

Holotype ♂ – Cambodia, Prov. Mondulkiri, Seima Biodiversity Conservation Area, [dwc:verbatimCoordinates: 12°57'N, 107°10'E], 3–8 July 2009 (Bae & Chae), gen. slide no. CIS-6072/Park. Paratype – 3♂, 1♀, same locality, 7 Oct. 2010.

This new species is similar to [taxon-name: Synersaga pseudocathara] from Myanmar, and [taxon-name: Synersaga kuni] and [taxon-name: Synersaga nigriptera] from Vietnam in the external and male genitalic characters. It can be distinguished from them by the shape of cucullus and the caudal processes of the juxta in the male genitalia. The caudal processes of the juxta of the new species are similar to those of [taxon-name: Synersaga nigriptera], but longer and arched inwardly, and the distal portion of the cucullus is more or less clavate.

Adult (Figures 1, 2, 3). Wingspan, 17–18 mm. Head and thorax dark fuscous dorsally. Antenna dark fuscous throughout, relatively thick. Second segment of labial palpus fairly thickened, dark fuscous on outer surface with orange white apex, orange white on inner surface; 3^rd segment slender, as long as 2^nd segment, orange white all around. Forewing covered with dark fuscous scales throughout; two blackish discal spots well developed: one in middle, the other larger one at end of cell; apex rounded; termen slightly concave medially; venation with R₁ arising from middle of cell; R₂ nearer to R₃ than R₁ at base; R₃ free; R₄ and R₅ stalked for basal 3/5 length; R₅ reaching just beyond apex; M₃ arising from half between M₂ and CuA₁₊₂ at base; CuA₁ and CuA₂ stalked for basal 1/5. Hindwing broader than forewing, pale brownish orange; apex more or less obtuse; termen sinuate; fringe concolorous, with narrow orange white basal line; venation with M₃ and CuA₁ short stalked. Hind tibia clothed with orange gray scales.

Male genitalia (Figures 4, 5, 6, 7). Uncus broad, short, obtuse, not exceeding basal stalk of gnathos, with small median lobe on caudal margin. Median process of gnathos strongly bent beyond middle, with acute apex. Valva broad basally, with triangular process near base on costa; costa gently concave; ventral margin gently arched outward in basal half; cucullus elongate, broadly expanded with round outer margin; dense long setae in basal half of cucullus, fairly setose beyond. Juxta with caudal processes long, gently arched inward, while the processes in [taxon-name: Synersaga nigriptera] nearly straight, clavate. Aedeagus gently curved, shorter than valva+cucullus, with finely dentate along ventral and dorsal margins apically; cornuti consist of a series of numerous needle-like cornuti. Abdominal segments in Figures 8 and 9.

Female genitalia (Figures 10, 11, 12). Similar to those of [taxon-name: Synersaga nigriptera]. Caudal margin of eighth abdominal sternite with deep Y-shaped medial emargination. Dorsal surface of ostial plate with dense spinules; caudal margin of ostium bursae concave. Antrum weakly sclerotized, cup-shaped. Ductus bursae coiled twice, slightly longer than corpus bursae, nearly same width throughout, with several needle-like spines internally. Corpus bursae elongate; signum a semiovate plate denticulate throughout.

Cambodia (Mondulkiri).

The species name is derived from the type locality.