carduus crispus,
welted thistle European biennial introduced in North America having flower heads in crowded clusters at ends of branches
carduus nutans,
musk thistle,
nodding thistle Eurasian perennial naturalized in eastern North America having very spiny white cottony foliage and nodding musky crimson flower heads; valuable source of nectar
Thistle is the common name of a group of flowering plants characterised by leaves with sharp prickles on the margins, mostly in the family Asteraceae. Prickles often occur all over the plant - on surfaces such as those of the stem and flat parts of leaves. These are an adaptation that protects the plant against herbivorous animals, discouraging them from feeding on the plant.