@markyscott
" And Winged elm can hybridize with American, which is also native to our area, because they're both spring flowering elms. So there are many potential variants and crosses that can occur, I think, which can make identification a bit tough."
From all of the scientific papers I have read on American (White or Water) Elms is they are tetraploid, (they have 2x the number of chromosomes), that is why ALL of the attempts to cross them with other species has failed. There is some recent speculation that "some smaller percentage of American Elms" are diploid that could allow them to cross with other species, but that would open an argument that it might be yet another species other than American Elm.
I have found a number of highly credible papers over the years from scientists and Governments on both sides of our borders that all basically agree that American Elms are tetraploid. Something they found when they were trying to cross the species to obtain DED resistant strains... and, only one "grower/nursery" claimed that they had successfully crossed an American Elm with another species, but the speculation was that it was actually another native species (I think a Slippery Elm), not a true American Elm, partially because the cross was never able to have been duplicated again, or since.
The reason that I personally believe that American Elms are indeed tetraploid, is that there was a HUGE effort to find a DED replacement for the Elms in Canada, and there was a great deal of resources that went into the projects. IMHO, if scientists (inside and outside of the Governments Programs and Universities) could not cross the elms within laboratory conditions using highly effective techniques, I'm pretty sure that it can't be done... especially in an "uncontrolled" environment. And IF it were possible to cross them in a rather uncontrolled environment, I'm pretty sure the nurseries on both sides of the border SK, MB, ND, MN, would have managed to get it done, because that would have been "really big business" for them if they had succeeded... and I know a lot of effort was put into getting a DED strain. (Mostly, attempts to cross American Elm with the highly DED resistant Siberian Elms... these attempts all failed, again on the premise of American Elms being tetraploid.)
I have come to believe that American Elms cannot be crossed with any other elm. But, every other native elm has a high likelihood of crossing with other elms (including Siberian Elms).
Today, because of the information you provided on Cedar and September Elms flowering in the fall (neither of which are native here), I guess I'll have to amend my philosophy.
It would be interesting to find out exactly how all of these particulars play out, but I don't have another 100 years left in me to wait around to find out the truth.
In any case, I'm not looking to argue, just thought I'd share some thoughts...
That is a terrific Elm you have there, we simply do not see the winged species here; Americans, Slippery (rarely), the ever invasive Siberians, and a hand full of hybridized Elms from nurseries of course.
