Which Black Eyed Susan is Which?
Do you want a black eye? Black eyed Susan, that is. Or is that a brown eyed Susan? The other day someone asked me how to differentiate this group of plants that, at first glance, look so much alike. Today, I will attempt to tackle that question here.
Those who know me know that I get really frustrated with common names for plants. Depending on where you live, the name black eyed Susan is used for a number of different yellow flowers with a dark center. The most common ones, at least here in southern Ontario, are Rudbeckia hirta (which I call black eyed Susan), Rudbeckia triloba (brown eyed Susan) and Rudbeckia fulgida (orange coneflower). However, these plants also come with a lot of other names that you might know them by, just to keep things confusing. For example:
Rudbeckia hirta (Black Eyed Susan) is also called Bristly Coneflower, Brown Betty, Brown-eyed Susan, Common Black-eyed Susan, English Bull’s Eye, Gloriosa Daisy, Golden Jerusalem, Poor-land Daisy, Yellow Daisy and Yellow Ox-eye Daisy.
Rudbeckia fulgida (Orange Coneflower) is also known as Black Eyed Susan, Brilliant Coneflower, Brown Eyed Susan, Orange Rudbeckia, Perennial Black-eyed Susan, Showy Black-eyed Susan and Showy Coneflower.
Rudbeckia triloba (Brown Eyed Susan) also goes by the names Thin-leaved Coneflower, Three-lobed Coneflower and Three-lobed Rudbeckia.
But it’s not just the names that can be confusing. To the uninitiated, these 3 flowers look very similar. And the descriptions you read about them don’t always help, simply because there can be so much variability within each species that, until you get to know the plants, the descriptions seem to overlap.
Rudbeckia hirta – Black Eyed Susan
Let’s start with Rudbeckia hirta, Black Eyed Susan. For me, the main differentiating characteristic is the fuzzy leaves and stems – fuzzy enough that the leaves actually appear to be a lighter colour than the other Rudbeckias. But fuzziness is a relative characteristic as all 3 have a certain amount of hairiness to the leaves and stems. Once you see the leaves side by side, however, you will easily tell them apart in the future (most of the time).
R. hirta leaves tend to be strap-like and, on average, tend to be longer and narrower than the other two. And they are ALMOST ALWAYS very hairy.
This plant is quite variable in its nature, though. It may be an annual, a biennial or even a short-lived perennial in some cases. And the genetic variability within the species can result in individuals with different petal shapes, different leaf shapes and sizes, and even a range of hairiness of the stem and leaves. But on average, the leaves and stems have a pale fuzzy appearance. If it’s late in the season, they also tend to die off in early fall (at least the annual and biennial ones do) whereas R. fulgida and R. triloba tend to stay green well into the late fall, even after the flowers have finished.
Rudbeckia hirta does well in full sun to part shade in just about any dry to moist, reasonably fertile, well-drained soil. This plant will grow to a little over 3’ tall and in the wild is found in fields, open woods and along roadsides.
R. hirta Native Range:
Rudbeckia fulgida – Orange Coneflower
This shorter statured plant is an extremely popular garden perennial, mainly because once it starts blooming it tends to put on a non-stop show for months. In most years in my southwestern Ontario garden, it starts to flower in late June or early July and keeps going till frost – sometimes as late as November, though after the drought we had here this year, they’ve pretty much finished blooming in mid-September.
A very common cultivar (or nativar, if you prefer) is Goldsturm. There are also even shorter cultivars, usually with the word “Little” somewhere in the name. The straight species typically grows 2-3’ tall, as does the Goldsturm variety. Most of the others are only 1-2’ tall. I have yet to find a definitive article on how Goldsturm is different from the true species. If you have the scoop on this, please let me know.
The leaves on R. fulgida tend to be much wider than on R. hirta and usually have fairly large serrations along the edges, especially on the lower leaves. As you can see in the photos, though, they may have no serrations at all. And though they may feel somewhat rough and hairy, they are not nearly as hairy (on average) as R. hirta.
One thing is for sure – R. fulgida produces a much denser mass of colour than R. hirta, and for a much longer period of time, though R. hirta always starts flowering a couple of weeks before this one does. It’s not that fussy about where it grows – it will do well in moist to dry, sandy to clay soils in full sun to part shade. I have a patch that is in full, light shade and it is doing just fine.
R. fulgida Native Range:
Rubeckia triloba – Brown Eyed Susan
Not native in Ontario, this nonetheless very popular short-lived (typically 2-3 years) perennial is the tallest of the 3 plants discussed here – in ideal conditions (full sun, moist loamy soil) it can get upwards of 5’ in height, though one writer indicated his plant hit 8’ tall!
The easiest way to differentiate R. triloba from the other two is to take a look at the leaves near the base of the plant. These are what give this plant its specific epithet (or species name) – triloba. The lower leaves have 3 (occasionally 2) lobes, as seen in the accompanying photo. The upper leaves look quite similar to R. fulgida, with the same variability in hairiness and serrations.
The other telltale difference is that R. triloba also tends to have a fairly reddish stem – sometimes it may be a deep solid burgundy colour, but on other plants it may be more of a striped stem. The stems are almost always fairly hairy.
Rudbeckia triloba is probably the fussiest of the 3 for growing conditions, but it is still quite versatile. It prefers moist to mesic loamy or sandy-loam soils, though some clay is tolerated. Like Rudbeckia fulgida, it blooms from July to first frost.
R. triloba Native Range:
If you have a native plant gardening related topic that you would like to know more about, let me know and I will add it to my growing list (pun intended). If it’s something I get multiple requests for, or is simply something that strikes my fancy, it will surely move up the priority list.
Happy Native Plant Gardening.