Callistemon is a genus of 34 species of shrubs in the family Myrtaceae, all of which are endemic to Australia. It is sometimes considered a synonym of Melaleuca, and four Callistemon species from New Caledonia were moved to that genus by Lyndley Craven and John Dawson in 1998. Callistemon species are commonly referred to as bottlebrushes because of their cylindrical, brush like flowers resembling a traditional bottle brush. They are found in the more temperate regions of Australia, mostly along the east coast and south-west, and typically favour moist conditions so when planted in gardens thrive on regular watering. However, at least some of the species are drought-resistant.
Bottlebrush seed capsules
Callistemons can be propagated either by cuttings (some species more easily than others), or from the rounded seeds. Flowering is normally in spring and early summer (October–December), but conditions may cause flowering at other times of the year. The obvious parts of the flower masses are stamens, with the pollen at the tip of the filament; the petals are inconspicuous (see picture). Flower heads vary in colour with species; most are red, but some are yellow, green, orange or white. Each flower head produces a profusion of triple-celled seed capsules around a stem (see picture) which remain on the plant with the seeds enclosed until stimulated to open when the plant dies or fire causes the release of the seeds. (A few species release the seeds annually.)
They are relatively slow growing though in time the larger species can grow up to 15 m (49 ft). Some are ground-hugging, and grow to only 0.5 m (1.6 ft). The leaves are linear to lanceolate and they are not deciduous.
They have been grown in Europe since a specimen of C. citrinus was introduced to Kew Gardens in London by Joseph Banks in 1789.
In Australia, Callistemon species are sometimes used as food plants by the larvae of hepialid moths of the genus Aenetus including A. ligniveren. These burrow horizontally into the trunk then vertically down.
In India, bottlebrush plants/trees are grown in gardens. Their leaves have a lovely fragrance which gets released on crushing the leaves with hands.