Bicoloured flowers are most common in plants that have been highly bred such as camellias, dahlias, roses and tulips. This often happens because the genes for flower colour in these plants can be quite unstable. This instability can also produce indiscriminate blotching and streaking of flowers.

Bicoloured flowers are usually seen as a randomly-occurring abnormality.

It is likely that these flowers result from a mutation in the initial development of the flower, probably when it comprises only two cells. At this stage, the genes that control flower colour in one cell experience a change. As the cells multiply, half are of the normal colour and half are the mutated colour. Because the process is random, it can change and sometimes the bicoloured flower display will not recur in subsequent years.

Many annuals, bulbs, herbaceous perennials and shrubs are affected. The following plants are a sample of many that are cultivated for their bicoloured flowers:

Impatiens F1 hybrid ‘Tutu Red Bicolor’: early flowering bright-red double and semi-double flowers highlighted with patches of snowy-white. Seed raised and bred for bicoloured flowers.
Pelargonium ‘First Blush’: regal pelargonium with white flowers each with a spreading blaze of red across the upper petals.
P. ‘Rouletta’: ivy-leaved pelargonium with semi-double, bicoloured light crimson flowers in clusters. Height 60cm (2ft).
Camellia japonica ‘Lavinia Maggi’ AGM: formal double white flowers with red and pink stripes, in early spring.
Cytisus ‘Zeelandia’: with creamy-white and lilac-pink in clusters, late spring and early summer. Height 1.5m (5ft).
Dahlia ‘Twynings Smartie’ AGM: single flowers have cerise and white petals.
Lupinus ‘The Chatelaine’: racemes of bicoloured pink and white flowers in early and mid-summer. Height 90cm (3ft).
Phlox maculata ‘Natascha’: an early phlox cultivar with white petals striped magenta. Height 90cm (3ft).
Rosa gallica var. officinalis ‘Versicolor’: very fragrant pale-pink flowers are striped reddish-pink. Height 80cm (32in).
R. ‘Ferdinand Pichard’: fragrant pale pink blooms with pink and red stripes produced from summer to autumn. Height 1.5m (5ft).
Salvia microphylla ‘Hot Lips’: shrubby aromatic evergreen with bicoloured red and white flowers from summer to autumn. Height 90cm-1.2m (3-4ft).
Tulipa ‘Estella Rijnveld’: a Parrot Group tulip producing fringed white-flamed red flowers in late spring. Height 55cm (20in).

Recently introduced shrubs:

Buddleja ‘Bicolour’: with pink and orange flowers in panicles, during summer.
Mahonia ‘Cabaret’: with yellow and orange flowers in panicles, late winter and early spring.