Cirsium is a genus of perennial and biennial flowering plants in the Asteraceae, one of several genera known commonly as thistles. They are more precisely known as plume thistles. These differ from other thistle genera in having feathered hairs to their achenes. The other genera have a pappus of simple unbranched hairs.
Cirsium
Cirsium arizonicum (Arizona thistle)
Cirsium canum (Queen Anne's thistle)
Bumblebee on thistle flowerhead (Cirsium arvense)
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 can also occur all over the plant – on the stem and on the flat parts of the leaves. These prickles protect the plant from herbivores. Typically, an involucre with a clasping shape similar to a cup or urn subtends each of a thistle's flower heads. The typically feathery pappus of a ripe thistle flower is known as thistle-down.
Milk thistle flowerhead
Cirsium arizonicum, showing arachnoid cobwebbiness on stems and leaves, with ants attending aphids that might be taking advantage of the shelter.
Thistles on Calton Hill in central Edinburgh, Scotland, 2023
Carduus nutans in the early morning light.