Siouan languages
Siouan or Siouan–Catawban is a language family of North America that is located primarily in the Great Plains, Ohio and Mississippi valleys and southeastern North America with a few other languages in the east.
Siwu language
Siwu has seven oral and five nasal vowels. Several languages of the region have 8- or 9-vowel systems with some form of vowel harmony. In Siwu, noun class prefixes do not harmonize, but root-internally there are some constraints on vowel co-occurrences, attesting to the earlier presence of a system of cross-height vowel harmony (Ford 1973). Siwu is a tonal language with three level tones on the surface: High, Mid, Low. Functional load of tone is high in the lexicon (minimal pairs) as well as in the grammar (tenses marked by tone).