Ethnologue, whose classification is based on studies of mutual intelligibility and lexical similarity from a multitude of sources, classifies the varieties of Akan as dialects of the overarching Akan language, which belongs to the Central Tano language family. Glottolog makes basically the same analysis, with the exception that the Akan dialect continuum is labeled "Akanic". According to work done by P. K. Agbedor, Fante, Twi (Bono, Asante and Akuapem), Sefwi, Wassa, Asen, Akwamu, and Kwahu belong to Cluster 1 of the speech forms of Ghana, defined as in Ethnologue by the level of mutual intelligibility. Cluster 1 may better be termed r-Akan, which do not have /l/ as a phoneme, while l-Akan refers to the Akan cluster comprising Nzema, Baoulé, Anyin and other dialects spoken mainly in the Ivory Coast, which have /l/ in place of /r/. Phonology The Akan dialects contain extensive palatalization, vowel harmony, and tone terracing. Consonants Before front vowels, all Asante consonants are palatalized (or labio-palatalized), and the stops are to some extent affricated. The allophones of are quite complex. In the table below, palatalized allophones which involve more than minor phonetic palatalization are specified, in the context of the vowel . These sounds do occur before other vowels, such as , though in most cases not commonly. In Asante, followed by a vowel is pronounced , but in Akuapem it remains . The sequence is pronounced . A word final can be heard as a glottal stop . There is also a nasalization of and of as and , when occurring before nasal vowels. The transcriptions in the tables below are in the order /phonemic/, [phonetic]. Note that orthographic is ambiguous; in textbooks, = may be distinguished from with a diacritic: . Likewise, velar () may be transcribed . Orthographic is palatalized . Vowels The Akan dialects have fourteen to fifteen vowels: four to five "tense" vowels (advanced tongue root, or +ATR), five "lax" vowels (retracted tongue root, or -ATR), which are adequately but not completely represented by the seven-vowel orthography, and five nasal vowels, which are not represented at all. All fourteen were distinguished in the Gold Coast alphabet of the colonial era. An ATR distinction in orthographic a is only found in some subdialects of Fante, but not in the literary form; in Asante and Akuapem there are harmonic allophones of , but neither is ATR. The two vowels written e ( and