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Wildlife Featured in this article
- Cuban tree frog
- Italian wall lizard
Wildlife stowaways hitchhike on ornamental plants
As the global ornamental plant trade blooms, so does the number of its unintended passengers
In 2016, Silviu Petrovan got an unexpected call from a florist in Sheffield, England. The floral designer asked him to identify a live frog that arrived in a shipment overnight. Petrovan, who studies humans’ effects on biodiversity and has a longstanding fascination with amphibians, first thought it was a prank. But it wasn’t: he was looking at a North Andean tree frog (Dendropsophus norandinus) from Colombia that arrived in England via a shipment of cut roses.
Petrovan wondered, if an animal as delicate as a frog could survive in a bulk flower shipment across the ocean, what other undetected species could travel the world in potted plants or rose bouquets?
In his lab at the University of Cambridge, Petrovan and his collaborators set out to understand the ornamental plant trade and its growing environmental risks. They published their findings in a new paper in BioScience.
To conduct the study, Petrovan’s team aggregated and analyzed import and export data about plants, bulbs, cut flowers and foliage. They also contacted customs agencies around the world and asked for access to data on interceptions of things such as nonnative wildlife in imports of ornamental plants. They only got data on nonnatives intercepted in the United Kingdom and the Netherlands. None of the other countries provided requested interception data. “The lack of available datasets is a major impediment to properly understanding environmental risks,” Petrovan said.
In addition to official data, the team analyzed two unpublished databases of accidentally discovered exotic amphibians and reptiles at flower and plant shops, ornamental plant greenhouses and airports in the Netherlands and the U.K.
“Just the tip of the iceberg”
Their analysis revealed a “considerable volume” of hitchhiker species in ornamental plant imports. In particular, potted olive trees from Italy and Spain have likely introduced various nonnative reptiles, including lizards, gecko and snakes, to the Netherlands and U.K. that may have the potential to wreak havoc on local ecosystems.
“What we’ve found here is likely just the tip of the iceberg,” Petrovan said. In the case of the invertebrate data the researchers received from the two countries, many of the contaminants couldn’t be identified to genus level, a job especially challenging for the often extremely diverse species coming from tropical producer countries. Petrovan noted a lack of resources and expertise needed to deal with the overwhelming volume of plants crossing international borders every day. “Even with the best will from the customs authorities, there are all these kinds of taxonomical baggage and logistical issues that make it difficult,” Petrovan said.

Invasion risk in the United States
According to the study’s global market analysis, the United States is among the top three importers of ornamental plants, including bulbs, live plants and foliage. The U.S. is the top importer of cut flowers, which Petrovan calls “the definition of a short shelf life.” Because of the need for rapid transport and travel through customs, these flowers pose a higher risk for importing hitchhikers compared to similar imports, like many agricultural products.
One example of an invasive species that international trade has already brought to the continental U.S. is the Cuban tree frog (Osteopilus septentrionalis). Research indicates that one of the pathways for Cuban tree frog establishment was horticultural shipments, especially in palm trees. This species, which was introduced to southern Florida in the early 20th century, has been steadily moving northward and causing ecological damage along the way. Cuban tree frogs, which are larger than native tree frog species, prey on native frogs and lizards, and their tadpoles outcompete native tadpoles for space and food. They can also cause power outages in the state by short-circuiting utility equipment.
Managing for the future
Petrovan and his colleagues found that the ornamental plant trade has doubled in value over the last 20 years, clocking in at over $23 billion in 2022. Production has ramped up in tropical areas like South America and East Africa, creating local employment in rural areas, but also additional concerns for biodiversity loss, aquifer depletion and pollution from the use of pesticides, many of which the U.S. and European Union have banned.

In some ways, the environment is at the whims of current trends. People are digging up 100-year-old olive trees from old olive groves in the Mediterranean region and shipping them across Europe, including England, for their popular use as ornamentals. These old trees have gnarled bark and lots of character, which gives them their commercial appeal, but also many hiding places for small vertebrates. The trees also tend to have large root balls that can conceal stowaway critters and are generally difficult for import officials to thoroughly inspect. Consequently, they have introduced the Italian wall lizard (Podarcis siculus) to much of Europe.
“While amphibians and reptiles come with risks, for us, they’re not actually the biggest worry,” said Petrovan. Stowaways like insects, snails, flat worms or any of these creatures’ eggs have a higher chance of becoming problematic, Petrovan said. They’re also both hardier and more difficult to detect.
While future horticultural trends and increasing trade are likely to bring their own ecological challenges, Petrovan emphasized that now is the time to consider how to make the industry more sustainable from an environmental and ecological perspective. Certification programs for suppliers and shifting imports from high-risk, resource-intense products like cut flowers to bulbs or seeds can help manage risks inherent in global plant trade.
Petrovan said that a comprehensive prevention strategy needs to begin with a robust reporting system. “I hope that more countries make these datasets available,” Petrovan said, adding that more investigation is needed on species that aren’t being identified in reports.
Header Image: A flower warehouse in the Netherlands, which is the world’s top exporter of ornamental plants and cut flowers. Credit: Naaldwijk Rijksoverheid