To say that the taxonomy of this species is confusing would be an under statement! Flora of the Great Plains says that Silphium speciosum = Silphium integrifolium. WSSA says Silphium speciosum = Silphium asperrimum, but the National List of Scientific Plant Names says that Silphium asperrimum = Silphium radula. The final result of all of this is that you should look at both pages 214 and 217 in Nebraska Weeds when making a determination.