Thanks for all the feedback, everybody. This was a really exciting discovery for me. I was eager to get a sanity check! A botanist familiar with Silphium said that he thinks that it is indeed a hybrid. Several of them actually. I counted half a dozen plants last night with intermediary characteristics, all of them in proximity to the S. brachiatum plant which tells me that was the mother. I won't say I'm worried about hybridization, but I'll be more alert in the years to come as I have an ever increasing population of Silphiums coming up from seed throughout my large prairie beds. I directly planted 11 different Silphium species into my garden. If 2 hybridized, I'm sure others will too. Hell, maybe they already have? I guess I need to go check each & every one of the 100+ Silphiums back there. LOL. Thanks, Dennis in Cincinnati