Australasian Science: Australia's authority on science since 1938

Weeds Still Evolving Invasive Potential

Weeds are still evolving hundreds of years after their introduction to the UK, and are unlikely to have yet reached their full potential as invaders, according to research published in Biological Invasions.

The study was made possible by the centuries-old British tradition of storing plant specimens in herbaria, enabling scientists to track the physical evolution of introduced plant species from the beginning of their invasion to the present day.

The research team, led by Habacuc Flores-Moreno while at The University of NSW, looked at three common weeds – Oxford ragwort (Senecio squalidus), winter speedwell (Veronica persica) and a willow herb (Epilobium ciliatum) – that were introduced to the UK as long as 220 years ago. “We found the weeds are getting better and better adapted to life in their new environment, so they will presumably become even more problematic invaders as time goes on,” says team member Prof Angela Moles.

“The findings are also relevant to Australia because we have weedy species here that are in the same biological families. Our evidence also shows that about 70% of weeds in the state of NSW have undergone substantial changes since they were introduced.”

Flores-Moreno, now at The University of Minnesota, examined changes that occurred in the leaf shape, leaf area and plant height of three weeds over the course of centuries. These characteristics reflect how plants adapt to new water, nutrient and light conditions.

The Oxford ragwort, first recorded in the wild in 1794, underwent about a 20% increase in both leaf area and plant height since its introduction. The leaves of the winter speedwell, first recorded in the UK in 1826, became rounder and 17% smaller, while plant height increased by 14%. And the willow herb Epilobium ciliatum, first recorded in in the UK in 1891, showed a 50% decrease in leaf area.

“The change in the species’ traits seemed to happen in spurts,” Moles said. “And all three invasive species showed evidence of change in at least one trait during the last 50 years. The capacity to keep changing long after being introduced could allow invasive species to spread to more and more diverse environments, leading to novel species interactions.”

Australia has a wide range of other Senecio species present, while Veronica persica and Epilobium ciliatum are present in Australia.