Tom's Blog

Monday, August 24, 2015

What about Rudbeckia triloba?

This is the time of year when Rudbeckia triloba (brown-eyed Susanis in bloom. It is either a biennial or short-lived perennial, and apparently spreads well from seed. It is a nice plant, and blooms at a time when many prairie/savanna plants are finished flowering. Gardeners also like it and it is easy to get started in a native flower garden.

For some reason, this species has a bad reputation among Wisconsin "purists", apparently because it is often found growing in disturbed areas such as roadsides, railroad tracks, stream banks, or even urban settings such as vacant lots. Is it native or introduced? 

Per Swink and Wilhelm (Plants of the Chicago Area): "Although it appears to be native to our area, its occurrence here [disturbed areas] often suggests an escape from cultivation, or at least a history of severe disturbance---not a stable native community."

Per Antonio and Masi (The Sunflower Family in the Upper Midwest): "Brown-eyed Susan has become a late summer garden plant" and "cultivars have been selected for the horticultural trade." 

Per Cochrane and Iltis (Atlas of the Wisconsin Prairie and Savanna Flora): "Considered to be native to our region, although often inhabiting severely disturbed communities."

On the other hand (Minnesota Wildflowers): "While a Minnesota species of special concern in the wild from loss of habitat to agriculture and invasive species, brown-eyed Susan flourishes in gardens across the state."

In order to get an idea of its Wisconsin distribution, I went through the Wisconsin Herbarium website for individual records of this species, with special attention to early collections (before prairie planting came into vogue). Although many of the collections were from what could be called "disturbed" areas (railroads, roadsides, lakeshores, stream banks), on 8/15/1947 Phillip Whitford found it in a "prairie relic" by Oak Hills Cemetery, Black Earth. 

Note that there are other "native" species that are found in "disturbed" areas. For instance, spiderwort (railroad ballast), flowering spurge (roadsides), glade mallow (roadsides and stream banks), black-eyed Susan (roadsides), and prairie dock (roadsides). 

Species that grow in disturbed areas are often thought to be invasive. However, there is no evidence that Rudbeckia triloba is invasive. We first planted this as a desirable species for open oak savannas around the year 2000. It has been in our prairie/savanna species list since 2002 but has never "taken over" any area in which it is growing. It is an attractive plant that makes a nice contribution to the late summer savannas and prairies. We don't mind that it is also grown in gardens. Dozens of other prairie and savanna forbs are also grown in gardens. 


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