Calothamnus is a genus of shrubs in the family Myrtaceae and is endemic to the south-west of Western Australia. They are commonly known as one-sided bottlebrush, although the name is not accurate because some species have flowers in cylinders or scattered around the stems. The flowers of Calothamnus quadrifidus are on one side of the stem, so the name one-sided bottlebrush is appropriate for that species. Calothamnus species are generally medium to tall woody shrubs with crowded leaves.