Hello Tanja,

I am not a specialist in Morchella - so please take my answer with caution.

Anyway, I think that your collection should be Morchella vulgaris - this is the form that is dealt with as M. spongiola in the paper of Kellner & al., as one of three species of the Morchella esculenta-complex growing in Central Europe. M. vulgaris is darker and longer staying dark compared with exculenta (crassipes) and americana (esculenta) - and the species with the least tree specifity (esculenta mainly growing with Fraxinus and americana with Populus).  Thanks to Pierre-Arthur Moreau who gave me some information.

I am looking forward to other opinions.

Best regards from Lothar