Upright shrub to 3 m tall, semi-evergreen in mild conditions. Twigs green to yellow-green into their second year, glabrous, four-angled; pith chambered. Leaves long-elliptic to lanceolate, 3–15 × 1–4 cm, apex acuminate, base cuneate; margin serrate or entire in the lower half; both surfaces glabrous; petiole 6–12 mm, glabrous. Flowers in mid spring, singly or in 2s or 3s (rarely 4s) at each leaf axil. Calyx lobes broadly ovate or elliptic, 2–4 mm long, ciliate. Corolla deep yellow, c. 3 cm wide, with narrowly oblong, revolute lobes. Fruit capsule 10–15 mm long. (Chang, Qiu & Green 1996; Bean 1981).
Distribution China Anhui, Fujian, Hubei, Hunan, Jiangsu, Jiangxi, NW Yunnan, Zhejiang
Habitat Ravines, streamsides, woodland fringes near rivers.
USDA Hardiness Zone 5-6
RHS Hardiness Rating H6
Conservation status Not evaluated (NE)
Forsythia viridissima is one of the commonest species in China, where it is also widely cultivated except in the far south of the county (Chang, Qiu & Green 1996). The Scottish plant hunter Robert Fortune first saw it as a garden plant in the coastal zone of Zhoushan (Wikipedia 2021) in 1844–5, and sent a plant to the Royal Horticultural Society in a Wardian case, which flowered in 1847 (Bean 1981). It is likely to have been represented in cultivation for a long time as a single clone descended from this plant, as the species was believed to be universally ‘pin-eyed’ (in contrast to the common clone of F. suspensa in Europe at this stage, which was ‘thrum-eyed’) (Bean 1981).
This forsythia is slightly less hardy than F. suspensa or than its Korean cousins (Wyman 1961), and was considered a failure at the Arnold Arboretum in coastal Massachusetts in the 1940s. In very mild conditions it can be semi-evergreen (Bean 1981), but it can also show the best autumn colours in the genus, in a range from lemon-yellow to purple. It is often one of the last of the genus to come into flower in the spring. The greenish colour of the young shoots, persisting even in full sun and lasting into their second year, is distinctive.
Forsythia viridissima was first experimentally hybridised with F. suspensa by Thomas Meehan in Philadelphia in the 1860s (Bean 1981). Similar hybrids (F. × intermedia) began to be sold in Germany around the turn of the 20th century, and quickly eclipsed F. viridissima itself as a garden plant. The species has also been sparing in its production of ornamental sports; forsythias such as ‘Broxenensis’ are sometimes placed under F. viridissima but really belong with F. koreana, which was often treated as a variety of this species. The gold-variegated ‘Variegata’ mentioned in the Dictionary of Gardening in 1951 (volume 2, p. 830) has either been lost to cultivation (Hatch 2021–2022) or was really F. koreana ‘Variegata’.
Synonyms / alternative names
Forsythia viridissima 'Klein's Autumnal'
A dwarf selection which flowers again in autumn in the conditions of the southern United States, albeit sparingly (Dirr 2009). It was selected by Theodore Klein at Yew Dell Farm, Kentucky, and is still grown in a few American collections. ‘Klein’s Autumnal’, represented at the Morton Arboretum in Illinois, seems likely to be the same thing, though Laurence Hatch (Hatch 2021–2022) states that this is an F. × intermedia selected for autumn colour. In the continental climate of the Dawes Arboretum in central Ohio, a plant grown as ‘Klein’ shows indifferent autumn colour, a greeny-yellow tinged with purple (Dawes Arboretum 2022).