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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. The term perianth is derived from the Greek peri, meaning around, and anthos, meaning flower, while perigonium is derived from gonos, meaning seed, i.e. sexual organs. In the mosses and liverworts (Marchantiophyta), the perianth is the sterile tubelike tissue that surrounds the female reproductive structure (or developing sporophyte).
In flowering plants, the perianth, also called the perigonium, consists of the calyx (sepals) and the corolla (petals). These may be described as being either dichlamydeous/heterochlamydeous in which the two components are clearly separate, or homochlamydeous, in which they are indistinguishable (and the sepals and petals are collectively referred to as tepals). When the perianth is in two whorls, it is described as biseriate. While the calyx may be green, it may also be brightly coloured, and is then described as petaloid. The corolla and petals have role in attracting pollinators, but this may be augmented by more specilised structures like the corona (see below).
When the corolla consists of separate tepals the term apotepalous is used, or syntepalous if the tepals are fused to one another. The petals may be united to form a tubular corolla (gamopetalous or sympetalous). If either the petals or sepals are entirely absent, the perianth can be described as being monochlamydeous.
|Types of perianth|
Both sepals and petals may have stomata and veins, even if vestigial. In some taxa, for instance some magnolias and water lilies the perianth is arranged in a spiral on nodes, rather than whorls. Flowers with spiral perianths tend to also be those with undifferentiated perianths.
An additional structure in some plants (e.g. Narcissus, Passiflora (passion flower), some Hippeastrum, Liliaceae) is the corona (paraperigonium, or paraperigon), a ring of adaxial tissue arising from the corolla, perianth or filaments. This may consist of separate appendages, or be united. Strap-shaped ligules, as in Asteraceae are an example.
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