Macro-Siouan languages
In the 19th century, Robert Latham suggested that the Siouan languages are related to the Caddoan and Iroquoian languages. In 1931, Louis Allen presented the first list of systematic correspondences between a set of 25 lexical items in Siouan and Iroquoian. In the 1960s and 1970s, Wallace Chafe further explored the link between Siouan and Caddoan languages. In the 1990s, Marianne Mithun compared the morphology and syntax of all the three families. At present, the Macro-Siouan hypothesis based on relations among Siouan, Caddoan, and Iroquoian is not universally accepted as proven.
Quapaw language
The Quapaw language does not conform well to English language phonetics, and a writing system for the language has not been formally adopted. All of the existing source material on the language utilizes different writing systems, making reading and understanding the language difficult for the novice learner. To address this issue, an online dictionary of the Quapaw language is being compiled which incorporates all of the existing source material known to exist into one document using a version of the International Phonetic Alphabet which has been adapted for Siouan languages.