Viburnum opulus (Guelder Rose, Water Elder, European Cranberrybush, Cramp Bark, Snowball Tree) is a species of Viburnum, native to Europe and Asia.
It is commonly grown as an ornamental plant for its flowers and berries, growing best on moist, moderately alkaline soils, though tolerating most soil types well. Several cultivars have been selected, including 'Roseum' (synonym 'Sterile', 'Snowball'), in which all the flowers are only of the larger sterile type, with globular flower heads. There is some confusion, as there are a few other bushes, including other members of the Viburnum genus, also referred to as "snowball bush". The shrub is also cultivated as a component of hedgerows, cover plantings, and as part of other naturalistic plantings in its native regions.
It is naturalised in North America, where it has been misleadingly re-named as "European Cranberrybush" (it is not a cranberry). The fruit is edible in small quantities, with a very acidic taste; it can be used to make jelly. It is however very mildly toxic, and may cause vomiting or diarrhea if eaten in large amounts (Plants for a Future). This can be reduced by drying the bark first. The dried bark is used in a tincture, known as "Cramp Bark," to alleviate painful menstrual cramps.
The Viburnum opulus (Kalyna) is the National symbol of Ukraine.