thistle

Article summary

flowerhead , showing arachnoid cobwebbiness on stems and leaves, with ants attending aphids that might be taking advantage of the shelter. Thistle is the popular 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. The spines vary considerably by species. For example, Cirsium heterophyllum has very soft spines, while Cirsium spinosissimum is the opposite. Typically, species adapted to dry environments are more spiny. The term "thistle" is sometimes taken to mean precisely those plants in the tribe Cardueae (synonym: Cynareae), especially the genera Carduus, Cirsium, and Onopordum. However, plants outside this tribe are sometimes also called thistles. Biennial thistles are particularly noteworthy for their high wildlife value, producing copious floral resources for pollinators, nourishing seeds for birds like the goldfinch, foliage for butterfly larvae, and down for the lining of birds' nests.…

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