What Makes a Plant a Weed?

Research into the invasive Jerusalem artichoke reveals characteristics that contribute to making a plant a weed.

| Fall 2018

  • artichoke
    Jerusalem artichoke is a remarkaby invasive plant, with a few specific adaptations that make it successful.
    Photo by Getty Images/Ilia Baksheev

  • artichoke

All weeds might be plants, but not all plants act like weeds. What gives certain species the power to outcompete others and thrive in almost any environment? According to research from the University of British Columbia (UBC), the answer is in the genes.

For this study, researchers looked specifically at the Jerusalem artichoke (Helianthus tuberosus), a plant prized for its nutritious tubers, but considered one of the most destructive invasive species in Europe. Not a true artichoke, this North American native was first brought across the Atlantic in the early 17th century for food production, though it was quickly replaced with the potato. Jerusalem artichokes rapidly naturalized along marshes and rivers, and outcompeted native species. The plants spread so quickly that they threatened the productivity of farm fields across the continent; today, some patches of Jerusalem artichoke are dense enough to be mistaken for farm fields.

Not only are such invasions unsightly, but they also represent significant financial and environmental costs. The United States alone spends more than $120 billion each year to keep invasive plant, insect, and disease species from overtaking wild spaces.

The UBC research team planted more than 700 invasive and noninvasive artichokes for study in a controlled plot at the university’s Vancouver campus. As the plants reached maturity, the researchers recorded their characteristics, seeking commonalities among the varieties that spread the farthest. The researchers found that tuber production was a defining characteristic for the most invasive subspecies.

The trait for increased tuber production also evolved independently at least four times in the test population. Increased tuber production meant that most offspring of the most invasive plants were clones of their parents, so they retained the tuber-production mutations and passed them to their own offspring. In optimal conditions, the test plants rapidly refined their responses to environmental stimuli, adapting more quickly to new circumstances than established species and outcompeting those species.

It’s still unclear why certain species evolve invasive traits more often than others, but these findings clarify some of the traits that make weedy plants successful. Such plants evolve quickly in response to the environment and may carry several genes with the potential to activate the trait that allows them to outcompete other species. The research paper was published in Nature in spring 2018; search for “evolution of invasiveness by genetic accommodation” to read it.



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