I have been breaking my head what specie this Helianthus could be.
Since a couple of years it grows in the local nature reserve.
It is one of the latest flowers to bloom making it a valuable food source for insects..
It grows very tall 1,5 to 1,8 m, the leaves feel very coarse.
Flowers are big (7-8cm)

Well, the stem and foliage sure look like "Long leaf sunflowers" or Helianthus longifolius.

http://alabamaplants.com/Yello...

Thanks Dave, but I have the impression that the leaves on mine are broader and bigger, hairier too, the flowers on mine look bigger and fuller and have dark centres, so I'm not sure..maybe it is a natural crossing with another Helianthus sp..or maybe Helianthus longifolius is very variable..

how about helianthus angustifolius

We had a couple other H. augustifolia ids:

The thread "Swamp Sunflower (Helianthus angustifolius)" in Plant ID forum
The thread "Mexican sunflower???" in Plant ID forum

Thanks Ginger and Dave!
Yes, Helianthus angustifolia looks a closer match in the flowers, also its habitat, 'mine' were growing on damp soil, the leaves feel like sandpaper indeed, but then I still think the leaves on mine look bigger and broader than on the pics of H.angustifolia...

Helianthus pauciflorus is possible? The petals and leaves are not quite a match I think, or don't think..

http://homepage.mac.com/chpeir...

http://wisplants.uwsp.edu/scri...

http://luirig.altervista.org/f...

Janet, that looks a perfect match!! I feel it, it is the right one!

Well it does look as close as you can get I think!

I found that because I had saved the Italian site and searched all the species they had listed.

Thanks, Janet, The English popular name; 'Stiff Sunflower' is a perfect description too of its growing habit!