About Trimeresurus gracilis Oshima, 1920
Trimeresurus gracilis is a small pit viper with a maximum total length of 60 cm (24 in). Its scalation pattern includes 19 or 21 rows of dorsal scales at midbody, 144–149 ventral scales, 43–53 subcaudal scales, and 7–8 supralabial scales. This species is endemic to Taiwan, where it occurs only at elevations above 2,000 m (6,600 ft) above sea level. The species' given type locality is "Mt. Noko, Nanto"; Zhao and Adler (1993) identified this location as "Mt. Nôkô, Nanto Co., central Formosa", which corresponds to Mount Nengkaoshan, Nantou County, Taiwan. One phylogenetic study found results that contradicted a common prior inference of a close relationship between Trimeresurus monticola and Trimeresurus okinawensis. Instead, the study suggested that T. okinawensis and T. gracilis share a sister relationship. The phylogenetic relationships uncovered in this study also indicate that the genus Trimeresurus dispersed into the Ryukyu region at least three separate times. The study also notes that Trimeresurus flavoviridis and Trimeresurus tularensis, both found in the central Ryukyus, were previously more widespread and diverse across surrounding regions than they are today.
