Family Viperidae Oppel, 1811 (3 species)

Viperini Oppel, 1811: 47, 50 (type genus Vipera Laurenti, 1768: 99).

A note on Trimeresurus spp. in Singapore

Since the early description of arboreal Asian vipers, much confusion concerning their species delimitation and taxonomy has resulted due to substantial similarities and overlap in colour pattern, specifically amongst green forms. In Singapore, several species of Trimeresurus have erroneously been documented, mainly T. erythrurus, T. fucatus, T. gramineus, T. popeiorum, and T. sumatranus. Trimeresuru s hageni was first recognised as T. sumatranus (Boulenger 1896). Lidth de Jeude (1886) separated T. hageni from T. sumatranus, but the designation was not formally recognised (e.g., Boulenger 1896) until Brongersma (1933) provided a more thorough examination. In addition, Trimeresurus sumatranus was also a junior synonym of Tropidolaemus wagleri (Vogel et al. 2007).

Previously, most populations of green vipers from India to Indonesia were recognised as T. gramineus (Vogel et al. 2004) until they were split into separate species based on differences in hemipene structure (Pope & Pope 1933). Cantor (1847c) first reported “ Trigonocephalus gramineus ” (T. albolabris) and “ T. gramineus Var. ” (= T. sabahi) from Singapore. After Pope & Pope’s (1933) division of T. gramineus, populations from northeastern India, east to Hong Kong, and south to Indonesia were recognised as T. albolabris and T. popeiorum (Smith 1937), with populations in the Malay Peninsula assigned to T. popeiorum. Later, Vogel et al. (2004) split T. popeiorum into T. fucatus and T. nebularis. Much recently, T. fucatus along with three conspecifics were all placed into T. sabahi (Wostl et al. 2016). Therefore, T. gramineus var. from Cantor (1847c), and T. gramineus from Blanford (1881) and Hanitsch (1897) are T. sabahi. Trimeresurus erythrurus was also split from T. gramineus (Boulenger 1912; Pope & Pope 1933), so the specimen mentioned by Blanford (1881) stored at the Raffles Museum likely also represents T. sabahi. As T. sabahi from Peninsular Malaysia (Tweedie 1983; Vogel et al. 2004), Borneo (Stuebing et al. 2014), and Sumatra (David & Vogel 1996; David et al. 2009) all occur only at montane elevations, it is unlikely that the specimens came from Singapore or that they belong to T. sabahi. Therefore, we must assume that T. gramineus from Singapore actually represent T. hageni or juvenile T. wagleri, despite sexual dimorphism in T. wagleri being well-known by that time.

Confusion arises from a letter from Ridley (1933) who wrote that “ L. gramineus, the plain green species, was the commonest poisonous snake in Cantor’s time-1840 to 1852”. Ridley (1933) also declared that he found it commonly in open, grassy fields, and that it was more common in NHMUK collection than T. wagleri. In describing the habits of T. wagleri, Ridley (1933) only mentioned that of adult females, pointing out how their black-and-yellow colouration is an adaptation for background matching in “sun-flecked foliage”. Ridley (1933) then went on to say that “[i]n my day L. gramineus had nearly disappeared, while L. wagleri was very common”. The disappearance of “ L. gramineus ” Ridley (1933) contributed to “burning of the open country”. The confusion stems from T. hageni being a forest-dwelling species (Tweedie 1983; David & Vogel 1996), and there being only two specimens of T. hageni at NHMUK from Singapore. Regardless, Singapore’s viperid species consist of T. hageni, T. purpureomaculatus (not discussed above), and T. wagleri.