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In page Asteraceae:

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Several members of the family are copious nectar producers[6] and are useful for evaluating pollinator populations during their bloom.[citation needed] Centaurea (knapweed), Helianthus annuus (domestic sunflower), and some species of Solidago (goldenrod) are major "honey plants" for beekeepers. Solidago produces relatively high protein pollen, which helps honey bees over winter.[11]