The perianth ( perigonium, perigon or perigone in monocots) is the non-reproductive part of the flower, and structure that forms an envelope surrounding the sexual organs, consisting of the Sepal (sepals) and the Petal (petals) or Tepal when called a perigone. The term perianth is derived from Greek language (, "around") and (, "flower"), while perigonium is derived from () and (, "seed, sex organs").
In the and Marchantiophyta, the perianth is the sterile tubelike tissue that surrounds the female reproductive structure (or developing sporophyte).
Flowering plants
In
, the perianth may be described as being either
dichlamydeous/
heterochlamydeous in which the calyx and corolla 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, known as
sepaloid, it may also be brightly coloured, and is then described as
petaloid. When the undifferentiated tepals resemble petals, they are also referred to as "petaloid", as in petaloid monocots or liliod monocots, orders of monocots with brightly coloured tepals. The corolla and petals have a role in attracting
, but this may be augmented by more specialised structures like the
corona (see below).
When the perianth 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.
Both sepals and petals may have stomata and veins, even if vestigial. In some taxa, for instance some and Nymphaeaceae, the perianth is arranged in a spiral on nodes, rather than whorls. Flowers with spiral perianths tend to also be those with undifferentiated perianths.
Corona
An additional structure in some plants (e.g.
Narcissus,
Passiflora, some
Hippeastrum,
Liliaceae) is the
corona (paraperigonium, paraperigon, or paracorolla), a ring or set of appendages of adaxial tissue arising from the corolla or the outer edge of the stamens. It is often positioned where the corolla lobes arise from the corolla tube.
There can be more than one corona in a flower. The milkweeds (
Asclepias spp.) have three very different coronas, which collectively form a flytrap pollination scheme. Some passionflowers (
Passiflora spp.) have as many as eight coronas arranged in concentric whorls.
[Engler and Prantl Naturlichen Pflanzenfamilian Band 21 page 503 (figure 232b)]
The pappus of Asteraceae, considered to be a modified calyx, is also called a corona if it is shaped like a crown.[
]
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