Individuals with lobed leaves are sometimes superficially confused with Ratibida species, particularly with R. pinnata, which does not have the distinctive cylindrical receptacle and disk of R. columnifera. The glabrous stem and peduncles of Rudbeckia triloba, and the greenish to brownish disk of Rudbeckia laciniata may help distinguish them. Sometimes characters of chaff (location and shape) and pappus cannot be avoided. There is no pappus in Ratibida pinnata; in those Rudbeckia species with lobed leaves it is a very short crown.
The rays of Rudbeckia are yellow, but often with some shade of red, orange, or purple on the basal half.
1. Leaves (at least the lower ones) ± deeply lobed (or even compound).
2. Disk yellow or greenish yellow (brownish when dry); stems and pedicels (except immediately below the heads) glabrous or essentially so; largest leaves (often low on plant and seldom collected) 5–7 (–9)-lobed.
2. Disk deep purple-red; stems and pedicels pubescent; largest leaves 3-lobed.
3. Receptacular chaff ± obtuse or rounded and glandular-puberulent at apex; rays yellow throughout.
3. Receptacular chaff (conspicuous among the disk florets) acuminate to a sharp point, glabrous throughout; rays usually with orange base.
R. triloba (in part)
1. Leaves all unlobed.
4. Receptacular chaff acuminate to a sharp awn-like point, glabrous throughout; leaves ± ovate, toothed; pappus a tiny crown.
R. triloba (in part)
4. Receptacular chaff acute to rounded (but not prolonged to a sharp point) and pubescent, minutely ciliate, or glabrous at the tip; leaves various; pappus various.
5. Stems and leaves sparsely pubescent with scattered soft hairs; mid-cauline leaves with narrowly to broadly ovate blades and distinct petioles; pappus a tiny crown; tips of receptacular chaff glabrous or minutely ciliate.
5. Stems and leaves coarsely pubescent with stiff, dense hairs; mid-cauline leaves ± lanceolate to oblanceolate, sessile or tapering into an often winged petiole; pappus none; tips of receptacular chaff pubescent.