Butler University researchers examined 2,800 dried plants collected around the city before 1940 and compared them with plants found at 16 field sites between 1996 and 2006, an article in the Journal of Ecology reported Friday.
Increasing urbanization, they say, has wrought major changes to Indianapolis's plant species.
Although the city supports about the same number of plant species -- around 700 -- there are fewer native plants and more non-native species, introduced from other parts of the world and spreading on their own, the study found.
Over the past 70 years, Indianapolis's native plants have been lost at a rate of 2.4 species per year, while over the same period 1.4 non-natives arrive each year, the researchers said.
"This study shows that our flora is becoming less distinctive," Rebecca Dolan, director of Butler's Friesner Herbarium, said.
Lost species include Queen-of-the-prairie, a member of the rose family last found growing in the city in 1935, and the Virginia bunchflower.
Foreign arrivals include the invasive Japanese knotweed and Amur bush honeysuckle.
"Japanese knotweed was brought to our area as an ornamental. It spreads readily by seed and by root sprouts, forming thickets that choke out native species," Dolan said. "Amur bush honeysuckle was once promoted by the USDA's Soil Conservation Service for erosion control and wildlife food, but we now know it does neither," she said.
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