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 are an adaptation that protects the plant from being eaten by 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. The comparative amount of spininess varies dramatically by species. For example, Cirsium heterophyllum has minimal spininess while Cirsium spinosissimum is the opposite.
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adaptation amount asteraceae characterised cirsium clasping common comparative cup dramatically eaten family feathery flat flower flowering group heads herbivores heterophyllum involucre leaves margins minimal name occur pappus parts plant plants prickles protects ripe shape sharp species spininess spinosissimum stem subtends thistle thistle's thistle-down typically urn varies
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