Kerria japonica

Kerria japonica, also known as the Japanese marigold bush or miracle marigold bush in the northern New England area and as yamabuki (山吹) in Japan, is a deciduous shrub in the rose family Rosaceae, native to China, Japan and Korea. It is named after William Kerr, who introduced the cultivar 'Pleniflora'. It is the sole species in the genus Kerria; its genus name is also used as a common name (kerria).

Description
Kerria japonica grows to  tall, with weak arching stems often scrambling over other vegetation or rocks. In the wild it grows in thickets on mountain slopes. The leaves are alternate, simple, 3–10 cm long, with a doubly serrated margin. The flowers are golden yellow, with five petals, and evenly-spaced along branches of new green growth. The fruit is a dry single-seeded achene 4–4.5 mm long.

Cultivation and uses
Kerria is valued in gardens for its golden yellow flowers, which appear in the spring. It is best grown with some shade from full sunlight to avoid blanching the flowers, and needs to be pruned after flowering to maintain health and vigour. Two cultivars have gained the Royal Horticultural Society's Award of Garden Merit, K. japonica 'Golden guinea' and the double-flowered K. japonica 'Pleniflora', commonly known as bachelor's buttons.

Pests and diseases
Since 2014 the UK's Royal Horticultural Society has been receiving reports from gardeners and horticulturalists of damage to plants of the shrub Kerria japonica. Symptoms include multiple red spots on leaves, and lesions on the stems, resulting in defoliation and eventual death. It has been determined that this infection is caused by the fungus Blumeriella kerriae, which is specific to the kerria. This highly contagious disease, known in English as kerria twig and leaf blight, was known in the U.S. but has not previously been observed on British plants. It is regarded as a serious threat to the cultivated kerria plants, which are popular garden shrubs.

References

External links

Category:Kerrieae
Category:Flora of Japan
Category:Flora of China
Category:Flora of Korea
Category:Plants described in 1771