Aegopodium podagraria, commonly called ground elder, is a species of flowering plant in the carrot family Apiaceae that grows in shady places. The name "ground elder" comes from the superficial similarity of its leaves and flowers to those of elder (Sambucus), which is not closely related. Other common names include herb gerard, bishop's weed, goutweed, gout wort, snow-in-the-mountain, English masterwort and wild masterwort. It is the type species of the genus Aegopodium. It is native to Europe and Asia, but has been introduced around the world as an ornamental plant, where it occasionally poses an ecological threat as an invasive exotic plant.

This herbaceous perennial grows to a height of 1 metre (3+1⁄2 ft) from underground rhizomes. The stems are erect, hollow, and grooved. The upper leaves are ternate, broad and toothed. It flowers in spring and early summer. Numerous flowers are grouped together in an umbrella-shaped flowerhead known as a compound umbel. This is divided into several individual umbels (known as umbellets). Each umbellet has 15 to 20 rays (pedicels) that are each topped with a single, small, five-petaled white flower. These are visited by many types of pollinating insects.

The fruits, produced in late summer and autumn, are small and have long curved styles.

Aegopodium podagraria is distributed widely in the temperate zone of western Asia and the whole of mainland Europe. It has been introduced elsewhere, including Ireland, the United Kingdom, the United States, Canada, Australia (including Tasmania), New Zealand, and Japan.

In Eurasia, it is used as a food plant by the larvae of some species of Lepidoptera, including dot moth, grey dagger and grey pug, although A. podagraria is not the exclusive host to any of these species.^{[citation needed]}

Seed dispersal and seedling establishment are typically limited by shading, and new establishments from seed are restricted to disturbed areas. However A. podagraria readily spreads over large areas of ground by underground rhizomes. Once established, the plants are highly competitive, even in shaded environments, and can reduce the diversity of ground cover and prevent the establishment of tree and shrub seedlings. Because of its limited seed dispersal ability, short-lived seed bank and seedling recruitment, the primary vector for dispersal to new areas is human plantings as an ornamental, medicinal or vegetable plant, as well as by accidentally spreading rhizomes by dumping of garden waste. It spreads rapidly under favorable growing conditions. Because of this it has been described as a nuisance species, and been labelled one of the "worst" garden weeds in perennial flower gardens.

Aegopodium podagraria has been introduced around the world, including in North America, Australia, New Zealand and Japan, most commonly as an ornamental plant. It readily establishes and can become naturalized in boreal, moist-temperate and moist-subtropical climates. It is an aggressive invader in the upper Great Lakes region and northeastern North America, Australia, Tasmania and New Zealand. It can pose an ecological threat owing to its invasive nature, with potential to crowd out native species. Because of its potential impacts on native communities and the difficulty of controlling it, it has been banned or restricted in some jurisdictions outside its native range, including in Connecticut, Massachusetts, Wisconsin and Vermont in the U.S.

Once established, goutweed is difficult to eradicate. The smallest piece of rhizome left in the ground will quickly form a sturdy new plant. All-green goutweed may be more persistent and spread more rapidly than ornamental, variegated goutweed varieties, making the all-green type particularly difficult to control. And all-green, wild type forms are known to reappear from seeds of variegated varieties.^{[citation needed]}