Perennial herb or shrub to 6 m or more tall with woody stems. Leaves more than 0.5 m long, divided 2-3 times, with up to 15 ovate to elliptic, toothed leaflets. Flowers erect or hanging down, ray florets yellow, sometimes with a red tip, ligulate florets mostly lilac but occasionally white or pink.
Guatemala to Colombia
The distinction between this species and D. excelsa Benth. is not always clear. The botanical revision of Sorensen notes the 3-7 primary leaf divisions of D. excelsa and 9-15 primary leaf divisions of D. imperialis. This suggests that plants cultivated in Melbourne (at least) are D. excelsa, although the horticultural literature has long treated D. imperialis, with bell-shaped nodding flowers, as the common Tree Dahlia.
Quite likely the available tree dahlias are hybrids. Pescott, in his The Dahlia in Australia published c. 1935, refers to a Tree Dahlia with unusual open flowers that were also pinker than those generally seen. It was assumed at that time to be D. imperialis and was named 'Leslie'. Pescott then described breeding experiments by Director J. Cronin at the Royal Botanic Gardens Victoria (Melbourne Gardens), between this 'Leslie' and D. imperialis. The results were superior open flowers varying from white to rich pink and were given names like 'Alba' and 'Occulata' for white flowers, 'Rosea' and 'Carnea' for lilac to pink flowers.
Source: (2002). Dahlia. In: . Horticultural Flora of South-eastern Australia. Volume 4. Flowering plants. Dicotyledons. Part 3. The identification of garden and cultivated plants. University of New South Wales Press.
