Thistle is the common name of a group of flowering plants characterised by leaves with sharp spikes 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.