By Amy Weiss

Sep 26 2019

Humans have a long history of moving and cultivating plant species. But the scope of this movement increased during post-Columbian colonialism and continues today with global trade.¹ Plants can be introduced to a new area for a number of reasons, but ornamental plants are the most common introduction.¹ While most introduced plants will remain in the garden or field, some use their existing dispersal mechanisms to escape and establish themselves elsewhere. These naturalized populations have the potential to become invasive, with economic or ecological consequences. With climate change, some ornamental plants previously limited by climate factors would be able to establish themselves or spread further than before.  

Strawberry guava (Psidium cattleianum, seen above) was brought to Hawaii from its native Brazil for its ornamental properties and fruit. It is now one of the worst invasive plants on Hawaii, and a serious threat to Hawaii’s native forests, due to a lack of natural enemies.² Besides people enjoying the fruit, non-native birds and pigs also eat strawberry guava; spreading its seeds to new areas of the islands.²

Japanese knotweed (Reynoutria japonica, also known as Fallopia japonica; seen below) was introduced to England and the United States as an ornamental plant from Japan; prized for its flowers and vigorous growth. Over a century later, in the U.K., banks can deny a mortgage if knotweed is found on the property—due to Japanese knotweed’s ability to grow from tiny plant fragments, its rapid growth rate, and its ability to grow through cracks in cement, walls, or floorboards.³ Rob Naczi, NYBG scientist, says that Japanese knotweed is one of the worst invasive species in Northeastern North America and “unless we do something we’ve not yet discovered—[it will] be successful in dominating the state of New York.”³

Click on the herbarium specimens below to see examples of plants that have escaped cultivation.