Not sure what the common name in Europe would be, but I am guessing the walnut you're growing would be what we call English or White Walnut?
The trees is a Canadian type, I got from UK.
The link shows the diferente available to me here.
http://www.walnuttrees.co.uk/WTC_leaflet_webversion.pdfHow ever I'm trying to grow some from nuts, and the mother tree from those is probably black walnut.
It was planted by a sailor(seaman) in 1890-1900, and he brought it back from the US.