Unfortunately both Plantnet and Vicflora separate Onopordum from all the rest of the thistles on the basis that the top of the receptacle at the base if the florests is smooth, while in the other thistles it has bristles or scales. Not a character most people think to look at. Cirsium vulgare flower heads are 12-50 mm wide, while those of Onopordum acanthium are 35-50 mm wide. The leaves of Onopordum acanthium are grey-green, the upper surface sparsely woolly. The leaves of Cirsium vulare are dark green and covered with small prickles. The stems of Cirsiu,m vulgare are cobwebby, while those of Onopordum acanthium are woolly or densely cobwebby, with wings about 10 mm wide. Neither Plantnet nor Vicflora mention any branching of the stems, which suggest that they do not branch. Looking at what I can see of these characters in the photos, I am inclined to agree with Mike.