Tom's Blog: Four Rudbeckia species

In our area there are four species of Rudbeckia that might be present in a remnant or restoration. Also, Ratibida pinnata is generally present and may sometimes confuse things. These species are commonly called coneflowers or black-eyed Susans. In the field it may be difficult to decide which is which. Because most of these species are planted in native plant gardens, there are numerous cultivars, often with additional names (for instance Rudbeckia hirta ‘Autumn Colors’ ‘Indian Summer’). Many of the commercial plant and seed companies don’t provide enough detail to permit easy identification.

Ratibida (yellow or gray headed coneflower) is the most straightforward to distinguish. Its ray flowers always hang down and its disk flowers are tall and compact, providing a characteristic flower structure.

Rudbeckia laciniata (cut-leaf coneflower) can be distinguished from the other Rudbeckia species because its disk flowers are yellowish or grayish-green rather than purple. Also, it lives in moist places and shores and its lower leaves are pinnately divided. Although laciniata is listed in Czarapata’s book as a potentially invasive species in the upper Midwest, we have never seen any evidence of it getting “out of hand” at Pleasant Valley Conservancy. It was already present in our wetland when we first started restoration, and has never “taken over”. It is a tall plant and provides a nice backdrop in the wet prairies.

Rudbeckia triloba (brown-eyed Susan) is easily distinguished because its lower leaves are tri-lobed. Also, its flowers are smaller, with the ray and disk flowers both shorter than the other species.

Rudbeckia triloba is a short-lived perennial which establishes well and readily self-seeds. Once planted in a prairie it should continue as a colorful species for many years, even though it may move around. Some Wisconsin “purists” question whether it is “native” to our region, since it can often be found in disturbed habitats. However, our experience at Pleasant Valley Conservancy is that it is well behaved, and provides an attractive color late in August when many other species are starting to fade. It also does well in the more sunnier areas of the savannas.

Finally, we need to separate hirta from subtomentosa. hirta has a simple narrow leaf, whereas subtomentosa has a dissected leaf, as shown in the photos. As always with leaf shape, the lower leaves tend to be more reliable than the upper ones. Even then, leaf shape can often vary, so that this character is not always reliable. The best character, from my observations, is the stem. hirta’s is stiff and hairy, whereas subtomentosa’s is smooth and glabrous. Run your hands up the stem and feel the difference.

Rudbeckia hirta (black-eyed Susan) is an annual, biennual, or short-lived perennial. Some botanists consider it an “aggressive weed”, but you will find it in almost every planted prairie in southern Wisconsin. It is very reliable in a prairie planting, easy to establish and provides guaranteed color by the second growing season. A single patch may not persist but it seeds well and should remain as a long-lived member of the prairie.

R. subtomentosa (sweet black-eyed Susan) is a long-lived perennial. At Pleasant Valley Conservancy we never knew we had this species until it was recently pointed out to us by a visitor. Sure enough, we found quite a bit of it in the Barn Prairie as well as in the wet prairie nearby. Where did it come from? Seed heads of these two species will be quite similar, and it seems likely that seeds of both species could easily end up in a single mix. So we undoubtedly planted it accidentally. According to the Herbarium records, it is found mainly in southwestern Wisconsin, along the lower Wisconsin and Sugar rivers. However, with so much prairie planting going on these days in Wisconsin, I suspect those restrictions will no longer apply.