Hello Blandine,

The thorny stems appear to be a type of Aralia ("Devil's Walking-stick"), though we cannot determine which while the plants are dormant as key features for identification are missing. One species is native and the other is invasive, though both can be aggressive spreaders. The native species does have good wildlife value, but understandably may still be undesirable if located close to a walking path or an area where children might be more likely to run into a spiny clump. Here is a document which details some of the features distinguishing the two species: https://www.nybg.org/files/scientists/rnaczi/Mistaken_Identity_Final.pdf You can either search for "Aralia" to find the entries, or look for pages 8-9 (of the publication; the document-reading program you open it up with might have it as pages 12-13). Here are two other pages that might be useful in making comparisons:

https://www.marylandbiodiversity.com/view/8829

https://www.marylandbiodiversity.com/view/2189

Although removal itself may be challenging because of their vigor, they can be taken out if desired.

Miri