The world's most widespread invasive species

With its six violet petals, yellow “eye,” and glossy leaves, the water hyacinth makes quite an impression. Also impressive: A cluster of these plants can double in size every two weeks. In fact, the mat of vegetation blanketing a lake can be so thick that it can lock boats in place, block photosynthesis of native aquatic plants, and kill off fish. The world’s most widespread invasive species—more so than even black rats—this pernicious freshwater weed from South America has taken over waterways in nearly every other part of the world. True story: In 1910, the US Congress considered a bill to introduce hippo farming as a way to both eat away at the vegetation—since hippos love consuming these plants—and solve a meat shortage.

The lack of hippo meat in US supermarkets makes it clear the plan went nowhere. But invasive species didn’t go anywhere either, and since 1910, the problems posed by non-native species have only increased. One of the five major drivers of biodiversity loss, invasive species also cost the global economy some $420 billion a year—according to an authoritative 2023 invasive species assessment. That’s why the 2022 Kunming-Montreal Global Biodiversity Framework (think Paris Climate Agreement but for plants and animals) makes fighting them a priority. If nothing changes, scientists estimate that non-native species may increase by more than a third between 2005 and 2050.