Forsythias, with their elegant sprays of four-petalled, yellow flowers clustered along leafless, pimply branches are common sights in British gardens in early spring. Today, forsythias have become horticultural clichés but before the early twentieth century, they were rare shrubs, sought after by gardeners eager to impress their peers. The genus comprises nine species (all but one from east Asia), two (Forsythia suspensa and Forsythia viridissima) are frequently planted, along with their hybrid, Forsythia x intermedia.
Syringa suspensa was discovered in China by Carolus Linnaeus's pupil Carl Thunberg in the mid 1770s. In 1804, it was transferred to the genus Forsythia, which was named in honour of the Scottish botanist, royal gardener and founding member of the Horticultural Society of London, William Forsyth.
By the 1840s, Forsythia suspensa was growing in Britain but Forsythia viridissima proved a more popular nineteenth-century garden plant. Forsythia viridissima was discovered by the Scottish plant collector Robert Fortune in 1844 on his first botanical expedition to China. Fortune, sponsored by the Horticultural Society, became famous for filling British gardens with Chinese ornamentals. John Lindley, in 1846, formally described Fortune's discovery, and included quotes from Fortune's journal: 'it [Forsythia suspensa] is a great favourite with the Chinese, and is generally grown in all the gardens of the rich ... wild amongst the mountains of the interior in the province of Chekiang [Zhejiang] ... I thought it even more ornamental ... than when cultivated in the fairy gardens of the Mandarins'.
The hybrid Forsythia x intermedia was discovered by Hermann Zabel in 1878 among forsythia seedlings growing in the municipal gardens of Münden, Germany. During the twentieth century, this hybrid proved to be a horticultural success, and numerous popular cultivars, e.g., 'Arnold Giant' and 'Spectabilis', were selected from it.
Forsythias display heterostyly, a mechanism by which some plants prevent themselves being self-pollinated. Individuals in a population have male anthers at the ends of long filaments, and female stigmas on the ends of short styles. Other plants, in the same population, have short filaments and long styles. Consequently, long-styled plants can only be pollinated by short-styled plants and vice versa. Darwin described this phenomenon in forsythia, and even corrected Joseph Hooker, Director of Kew, who believed forsythias had separate male and female plants. Since most forsythias in gardens are cultivars propagated as clones, it is rare to find both flower types; short-styled forms are more common than long-styles forms.
de Wolf GP and Hebb RS 1971. The story of Forsythia. Arnoldia 31:41-63.