Sunday, August 22, 2021

Plant Profile: Brown-eyed Susan

 Flowers of brown eyed Susan with yellow petals and dark brown, mounded centers.


Brown-eyed Susan, Rudbeckia triloba, is a rare find in the wild. Although this native annual or short-lived perennial grows throughout the eastern U.S., it reaches the northwest limit of its natural range in Minnesota. Here it’s a state-threatened species, documented in open woods and floodplain forests in a handful of counties in the southeast part of the state. Both habitats continue to lose ground due to land conversion and invasive plants such as common buckthorn, making a natural population of brown-eyed Susan an exceptional discovery.

Although wild populations of brown-eyed Susan are hard to find, intentional plantings are not. This late-summer bloomer is popular in gardens and naturalized landscapes across the state. It’s in its peak season of flowering in late summer, an ideal time to look for and identify this plant.

How to Identify Brown-eyed Susan

Brown-eyed Susan is easiest to recognize by its profusion of 1- to 2-inch-wide flower heads. Each head is a collection of small flowers called florets. The center of the head, called the disk, is a button-shaped, mounded or conical structure bearing dark purple to brown disk florets. Around the disk are 6-13 ray florets, small flowers bearing a single, yellow-orange, petal-like ray. The rays are grooved along their length and have small notches at their tips. Flowering is from August into October (2, 3, 4).

Brown-eyed Susan can also be identified by its leaves and stems. It’s a tall plant, commonly 2-4 feet but up to 5 feet, with reddish, bristly stems. The leaves are also bristly on both surfaces. The lower leaves often have three lobes, the source of the specific name triloba and another common name, three-leaved Rudbeckia. (The latter is a misnomer; lower leaves are three-lobed but are not divided into three leaflets.) The lobed, lower leaves are stalked, whereas the upper leaves are lance-shaped or elliptic with short or no stalks. Because the plant tends to branch widely, it can look bushy, but smaller plants have fewer branches.

As noted above, natural habitats are low, open woods and floodplain forests, but brown-eyed Susan also grows in the moist soils of thickets and stream banks (4). Favorable garden locations should provide sun to part shade and moist, loamy soils.

Look-Alikes

Black-eyed Susan (Rudbeckia hirta) and orange coneflower (Rudbeckia fulgida) are the most common look-alikes. Compared to either species, brown-eyed Susan is taller and more branched with reddish-green stems. Its flower heads are 1-2 inches across, smaller than other Rudbeckia species. Brown-eyed Susan also blooms later and longer into fall.

Sweet Coneflower (Rudbeckia subtomentosa) is also like Brown-eyed Susan. Its natural range barely extends into southeastern Minnesota from its broader range to the south and east. Like Brown-eyed Susan, it is a tall plant – up to 6 feet – and some of its leaves may be three-lobed. However, its flower heads are wider, 2-3 inches across, and both the leaves and the bracts below the heads are described as being dotted with glands (2). This may require a magnifying lens to see. Although rare in the wild, sweet coneflower is planted in gardens.

Wild golden glow (Rudbeckia laciniata), another look-alike, grows 5-10 feet tall in moist thickets, woodland edges, swamps and floodplains (2). Unlike brown-eyed Susan, its flower heads are 2-3 inches across. Its leaves are much larger – up to 10 inches long with three to seven deep lobes. For that reason, wild golden glow is also called cut-leaf coneflower.

Below are photographs of brown-eyed Susan and two of its look-alikes, black-eyed Susan and orange coneflower.

Brown-eyed Susan, Rudbeckia triloba. Stems are widely branched, reddish-green, and bristly. Flower heads are 1-2 inches wide. Bracts are hairy-bristly, tapered, and of unequal length. Lower leaves are three-lobed and coarsely toothed (2). 




Black-eyed Susan, Rudbeckia hirta. Plants are up to 3 feet tall with few branches. Flower heads are 2-3 inches wide with numerous, densely hairy, tapered bracts. Stems are green and densely hairy (hirta is from the Latin prefix hirt, meaning hairy or rough). Leaves are densely hairy on both surfaces, lance-elliptic, and with edges that are smooth or finely toothed.




Orange Coneflower, Rudbeckia fulgida, is native to the eastern U.S. but not Minnesota (5). It is common in gardens. Plants are up to 3 feet tall and somewhat branched. Flower heads are 2-3 inches wide with bracts that are more sparsely hairy than either Brown-eyed or Black-eyed Susan. Stems are green and bristly-hairy. Largest leaves are coarsely toothed but not lobed. Cultivars of Orange Coneflower may have slightly different characteristics. 



References

(1) Minnesota Department of Natural Resources, Division of Ecological and Water Resources. 2018. Rare Species Guide: an online encyclopedia of Minnesota's rare native plants and animals [web application]. Minnesota Department of Natural Resources, St. Paul. www.dnr.state.mn.us/rsg. Accessed August 19, 2021.

(2) Minnesota Wildflowers. Webpages for Rudbeckia triloba, R. hirta, R. laciniata, and R. subtomentosa accessed August 19-21, 2021, at  https://www.minnesotawildflowers.info/.

(3) Brown-eyed Susan, Rudbeckia triloba. Wisconsin Horticulture, Division of Extension, University of Wisconsin-Madison. Website accessed August 19, 2021, at https://hort.extension.wisc.edu/articles/brown-eyed-susan-rudbeckia-triloba/

(4) Tallgrass Prairie Wildflowers: A Field Guide. 1995. Text by Douglas Ladd, Photos by Frank Oberle. Published by Falcon Publishing, Inc., in cooperation with The Nature Conservancy.

(5) USDA, NRCS. 2021. The PLANTS Database (http://plants.usda.gov, 08/21/2021). National Plant Data Team, Greensboro, NC USA. [Web page for Rudbeckia fulgida accessed 8/21/21 at https://plants.usda.gov/home/plantProfile?symbol=RUFU2.]


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