What is "double-flowered"

"Double-flowered" describes varieties of flowers with extra petals, often containing flowers within flowers. The double-flowered trait is often noted alongside the scientific name with the abbreviation fl. pl. (flore pleno, a Latin ablative form meaning "with full flower"). The first abnormality to be documented in flowers, double flowers are popular varieties of many commercial flower types, including roses, camellias and carnations. In some double-flowered varieties all of the reproductive organs are converted to petals — as a result, they are sexually sterile and must be propagated through cuttings. Many double-flowered plants have little wildlife value as access to the nectaries is typically blocked by the mutation.