Cirsium vulgare (Bull thistle)
Image credit: Jonathan BorbaIdentification tips
Tip #1: the genus name Cirisium comes from the Greek kirsion, which means swollen vein; an allusion to the use of this plant in antiquity in the treatment of swollen veins. And vulgarum that comes from Latin that means common. This is hard to create some analogy, so you have to decorate it yourself.
Plant shape
2º Identification tip: standing biennial plant with thorns in leaves and stems. In the first year, the plant develops in a rosette in the second year generates branches and flowers. This weed is often confused with Carduus nutans (musk thistle), but the leaves of mature musk thistle plants usually have no hair. Also, Cirsium arvense (Canada thistle) is a perennial plant of rhizomes, and young plants do not develop as a rosette, unlike bull thistle.
Leaves
3º Identification tip: the leaves are arranged alternately, are lanceolate with deeply cut margins and rigid thorns in the lobes. The leaves have many hairs on the top and softer whitish hair below.
Stem
4º Identification tip: the stems have leaves with prickly wings, with rough hairs on the upper surface and softer whitish hair below.
Flowers
5º Identification tip: flowers can be arranged in agglomeration or solitary at the ends of the branches. Reddish-purple coloration and surrounded by bracts with prickly tips.
Seeds
6º Identification tip: the seed is brown with a tuft of long whites to transport it to the wind, favoring the spread of the species.
Seedlings - the terror of all
8º Identification tip: cotyledons are egg-shaped, young leaves develop as a rosette. The leaves are oblong, with small thorns along the shores. From the second true leaf, the subsequent leaves contain many hairs on the upper surface.
Extra references:
https://weedid.missouri.edu/weedinfo.cfm?weed_id=65
https://extension.psu.edu/bull-thistle-identification-and-management