Short answers, pulled from the story.
Cirsium thistles have a pappus of feathered, branching hairs on their seeds, distinguishing them from related genera such as Carduus, Silybum, and Onopordum, which have simple unbranched hairs. This feathered pappus allows Cirsium seeds to disperse farther on the wind. The lectotype species of the genus is Cirsium heterophyllum.
Cirsium contains 493 accepted species. The genus is mostly native to Eurasia and northern Africa, with about 60 species from North America. Several species have been introduced outside their native ranges.
Cirsium vulgare is listed as a noxious weed in nine US states because it is a non-native invasive species there, sometimes called bull thistle. At the same time, a UK study by the AgriLand project ranked it in the top ten for nectar production, and a separate British study ranked it third for nectar sugar output per floral unit at 2,323 micrograms. It also supports the larvae of the Painted Lady butterfly Vanessa cardui and provides seeds for birds including the European goldfinch Carduelis carduelis.
The Painted Lady butterfly Vanessa cardui uses Cirsium vulgare as a larval food plant. The monarch butterfly Danaus plexippus relies on tall thistle, Cirsium altissimum, as a nectar source during its migration, a connection highlighted by the Xerces Society.
Cirsium comes from the Greek word kirsos, meaning swollen vein, which is the ancient Greek word for thistle. The name reflects the historical association between the plant and swollen veins.
Cirsium oleraceum, the cabbage thistle, is cultivated as a food source in Japan and India. Cirsium setidens, known as gondre, is used as a vegetable in Korean cuisine. Cirsium monspessulanum, Cirsium pyrenaicum, and Cirsium vulgare have traditionally been eaten in rural areas of southern Europe.