Thank you all very much! It is effectively Epimedium perralchium, called Frohnleiten in german language. It is because of I did not move from my conviction of the plant being a Brassicaceae that I wasn't able to identify it. Now I acknowledge that, apart from the four petals and the silicula-shaped fruits, it made a very doubtful Brassicaceae. I have seen it already a few times about Winterthur, standing 12-16 inches hihg. It is used as a gardening plant here.

Well from what I have read, the native Carolina buckthorn (Rhamnus caroliniana) has showy fall foliage. The buckthorn around my house is a soft brown with maybe a hint of orange. Very plain and ugly. However, the leaves look longer than the non-native Rhamnus cathartica and much more like Rhamus caroliniana. I am now pretty sure it is the native. Thanks everyone who replied, especially esh_ga! Now I will have another topic of discussion with my dad next time he comes over and we walk around in the woods. So the final verdict is: 1. Carya Tomentosa (mockernut hickory) 2. Sambucus canadensis (elderberry) 3. Sassafras albidum 4. Rhamus caroliniana (buckthorn) Never thought you guys would nail it this fast when I was taking pics yesterday :)

i found them very short lived in z5 MI .. so i would NOT mess with success ... and go digging them up ... and by short lived.. i mean a few years.. until the one bad winter ... they are.. most likely.. irrelevant to each other.. so do nothing different than you would for one.. do NOT double fert for example ... i think one of mine was killed.. by a very mild MI winter .... and late fert'g.. and it did not harden off properly before the reality of a MI winter set in ... and then repeated freeze/thaw.. killed it ... ken

Thanks Steve for all that information