Ulmus pumila and U. minor hybridize freely, there's lots of literature on this.  Therefore, in any area where both occur there will be many hybrids, and backcrosses of hybrids. Individual elms in such areas will have mixtures of characteristics.  You'll find morphological 'pumila' that nevertheless have these corky 'wings' on twigs,  you'll also find morphological 'minor' that nevertheless have small buds.  These individuals cannot be assigned to any nominate species.  DNA sequencing shows individuals to be complex mixtures (e.g. Biological Invasions 15(12) · December 2013).  Indeed, where hybridization is so frequent, it's an open question whether nominate species like 'minor' or 'pumila' are really phylogentically distinct.  Incidentally, these corky outgrowths are common on U. minor in the areas I know (France, Germany, UK).  

Dear Friend：

I am not a researcher on forestry. but I got the following information for you. The Siberian Elm cultivar Ulmus pumila 'Harbin' is an older Manchurian selection.

Kindly

Li Kangmin

emeritus Prof 

CAFS

Here in Czechia Ulmus minor creates outgrowths on branches pretty often.

Yours sincerely,

Ondrej Vitek

Thanks everyone who answered!

Andrei, I agree with your statement. In Ukraine Ulmus minor forms outgrowths on branches too. But in these exemplars elm –  the buds is smaller than that of Ulmus minor (2.2-3 mm), and only 4 renal scales, as in Ulmus pumila. Maybe it's a hybrid?

Sincerely yours

Ivanko Irina

Sorry, I´m not Botanist,

Aurelio

Aurelio, thank you for your interest and attention. But botanists are silent!

Irina

It should be Ulmus minor, in case of hybrid, at least one of the parents

Ulmus pumila and U. minor hybridize freely, there's lots of literature on this.  Therefore, in any area where both occur there will be many hybrids, and backcrosses of hybrids. Individual elms in such areas will have mixtures of characteristics.  You'll find morphological 'pumila' that nevertheless have these corky 'wings' on twigs,  you'll also find morphological 'minor' that nevertheless have small buds.  These individuals cannot be assigned to any nominate species.  DNA sequencing shows individuals to be complex mixtures (e.g. Biological Invasions 15(12) · December 2013).  Indeed, where hybridization is so frequent, it's an open question whether nominate species like 'minor' or 'pumila' are really phylogentically distinct.  Incidentally, these corky outgrowths are common on U. minor in the areas I know (France, Germany, UK).  

Thank you, dear colleagues.

To be honest, I first saw such specimens in urban conditions among thickets of Ulmus pumila. U. minor in the steppe zone in dry conditions of the steppe (along forest edges, on slopes) almost never forms such pronounced corky outgrowths. There may only be mild growths. In the classical Ulmus suberosa (photo) in the natural environment, corky outgrowths are very large. I will seek literature on this issue and contact my geneticists. We have fenced the thickets and will follow the trend.

Irina

Sorry for late reply. I was away from civilization. Ulmus suberosa is absent in the research area and adjacent territories. It is not found in our city at all. But, according to personal observations, in the Dnipropetrovsk region in the last 5-7 years Ulmus suberosa increases its number. It began to grow along rural roads, on the fringes of outer artificial woods.