There are many assumptions about the origin that small citrus unshu of China was imported to Yatushiro, Higo Province (today's Yatsushiro City, Kumamoto Prefecture) about 800 years ago and planted in Arida, Kishu (today's Arida District, Wakayama Prefecture) and thus named as "Kishu" because it grew to be a big industry there, and other assumptions say that citrus unshu (mikan) grew wild in Kishu and so on.
約800年前に中国原産の小ミカンが肥後国八代（現熊本県八代市）に伝わったのが元であり、それが紀州有田（現和歌山県有田郡）に移植され一大産業に発展したことから「紀州」の名が付けられたとの説の他、元々紀州有田に自生していたという説等がある。