Complex sentence: The perianth (sometimes called perigonium or perigon) is the non-reproductive part of the flower, and structure that forms an envelope surrounding the sexual organs, consisting of the calyx (sepals) and the corolla (petals).
Split into simpler sentences: The perianth (sometimes called perigonium or perigon) is the non-reproductive part of the flower, and structure that forms an envelope surrounding the sexual organs. In flowering plants, the perianth, also called the perigonium, consists of the calyx (sepals) and the corolla (petals).