(榕江县水尾水族乡水尾村) Yang'an 阳安 Banliang, Tangzhou township, Sandu County (三都县塘州乡板良村) Tangnian, Tanglian village, Benzhai township, Dushan County (独山县本寨水族乡塘联村塘年寨) Pandong 潘洞 Gaorong, Jiaoli township, Sandu County (三都县交梨乡高戎村) Pandong, Yanghe township, Duyun City (都匀市阳和水族乡潘洞村) Using computational phylogenetics, Castro & Pan (2014) classify the Sui dialects as follows. Pandong was the first branch to split off from Proto-Sui, followed by Yang'an and then Sandong. Within Sandong, the Southern dialect is the most divergent. Sui Pandong 潘洞 dialect (branch) Yang'an 阳安 dialect Sandong 三洞 dialect Southern (core) Western, Central Eastern Vietnam Sui is also spoken in Hồng Quang Village, Chiêm Hoá District, Tuyên Quang Province (62 km northwest of Chiêm Hóa township). In Vietnam, the Sui people () are officially classified with the Pà Thẻn people. The Sui numbered only 55 people as of the 1982 Vietnamese census, and numbered about 100 people as of 2001. Since Pa-Hng (Pà Thẻn) and Tày are also spoken in Hồng Quang Village, many Sui are also fluent in those two languages. The elderly Sui people of Hồng Quang claim that 8 Sui families had migrated to Vietnam from China 100 to 200 years ago, 2 of which have now already assimilated into other ethnic groups. Edmondson & Gregerson (2001) have found that the Sui dialect of Hồng Quang is most similar to the Sandong 三洞 dialect of Sui as spoken in Shǔilóng 水龙, Sandu Shui Autonomous County, Guizhou. Phonology Sui has seven vowels, . Diphthongs are . There are six or seven tones, reduced to two in checked syllables. The tones of the Sandu Sui Autonomous County, Guizhou, listed by conventional tone numbers, are: The alternate checked tone 7 is found on the long vowel . Tone 8 is somewhat variable on a long vowel, appearing in different locations either higher or lower than the short allophone, but always falling, as in tones 2 and 4. In some villages, tone 6 is two phonemes, in native words and in Chinese loanwords. In the village of Ngam, Libo county, tone 1 is low , the others as above. Consonants in parentheses were reported by the 1956 dialectology study Shuiyu diaocha baogao, but not in Li Fang Kuei's 1942 research in Libo County. (Labio-velars were not listed separately, so it's not clear if they also existed.) only occurs phonemically in the Southern Sui dialects. is classed as a labial because it can be followed by a glide . can also