In
flowering plants, 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
pollinators, 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
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.
Corona :
A. inferior ovaryB. The
calyx is a crown-shaped
pappus, called a
corona.
C. Anthers are united in a tube around the style, though the filaments are separate.
D. A ligulate petal extends from the tubular corolla.
E. style and stigmas An additional structure in some plants (e.g.
Narcissus,
Passiflora (passion flower), 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. The
pappus of
Asteraceae, considered to be a modified calyx, is also called a corona if it is shaped like a crown. == References ==