I have Echinacea tennesseensis (sp) in a separate bed by itself. It drops seed every year and I get new sprouts which are true to the mother plant.
Elsewhere in my yard I have Echinacea purpurea cultivars Magnus, Doppledecker, and Prairie Splendor.
This year, the E. tenn. sprouts have varied. Some are true to the mother and some have already grown into what appears to be a possible cross between the other Echinaceas. Is this even possible? There is not any way that the seeds from the other Echies could have gotten into this isolated, raised bed.
Yes, at least they are in the same genus, so it's likely possible (however generally speaking, interspecies hybridization is a lot less common than people like to think). So, yes, it could be, assuming you are seeing truly intermediate characteristics between the two species (not just in flower form but in other characteristics as well).
Without knowing more about your seedlings, it's hard to discount that your various named cultivars of E. purpurea may also have seeded out into various somewhat different forms (as only a clone of any of these would be guaranteed to come true) and that the seeds were blown around by the wind. (I think you'd be amazed at how seeds can be blown around and redistributed by the wind - I've had 3 native species show up in my urban yard, where I don't know of any populations nearby, nor does anyone else in the neighborhood grow them, or much of anything else).
Hmmm well I had forgotten about that 30 mph wind we had ALL summer long last year. That could very well explain it.
I do see some of the traits of the E. tenn. in the offspring, though. These are taller, with wider leaves, but they have space between the petals, ragged edges on the petals, and the petals are sort of cupped around the center, but not as drastically as the true E. tenn. I will see if I can get pictures.