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sympetalous(of flowers) having a structure in which the petals are fused to form a tube-like shape, as in the primrose and convolvulus. Other flowers, such as the buttercup and tulip, have petals which are completely free, i.e. polypetalous.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005