Calyx: The calyx is usually green, sometimes
colored. It may be regular, symmetrical, or irregular. It may be polysepalous
or gamosepalous. The calyx may be modified into a pappus, as in the Asteraceae
family. One of the sepals may be modified into a large leaf, often yellow or
orange, and sometimes crimson or white, as in the Messinda.
Duration: If the calyx falls off early, it is
known as a caducous calyx, as in poppy. If it falls off when the flowers
wither, it is called a deciduous calyx. If it remains attached to the fruit, it
is known as a persistent calyx. A persistent calyx may have a withered appearance,
as in cotton (Figure 1a), or it may be tender and ripe, as in eggplant (Figure
1b). Or it may be swollen, containing the fruit within, as in balloon vine,
gooseberry (Figure 1c), and wild foxglove. Or it may be somewhat fleshy, as in
hibiscus (Hibiscus sabdariffa) (Figure 1d). Or it may be fleshy,
colored, and completely encircle the fruit, as in duranta (Figure 1f).
Corolla: The corolla is either regular,
unisymmetrical, or irregular. Its petals may be fused or free. The fusion of
the petals may be complete or partial. Therefore, the corolla has many forms.
- Forms of Corollas
Actinomorphic and polypetalous (or
dialypetalous) corolla
Cruciform: Petals are differentiated into a
claw and a limb, and all four petals are arranged in the form of a cross, e.g.,
members of Cruciferae.
Caryophyllaceous: When five petals are clawed and have
their limbs spreading out, e.g., members of Caryophyllaceae.
Rosaceous: When five or more petals are
spreading like that of a rose, e.g., Rosaceae.
Campanulate: Bell-shaped corolla, e.g.,
Campanula, Physalis.
Tubular: Regular, gamopetalous corolla with
their petals fused to form a tube, as in disc florets of Compositae.
Infundibuliform: Regular, gamopetalous corolla with
its petals in the form of a funnel, e.g., members of Convolvulaceae.
Hypocrateriform: Regular, gamopetalous,
salver-shaped corolla, i.e., the basal portion is narrow and tubular with the
abruptly expanding flat apical part, e.g., Clerodendron.
Urceolate: Urn- or pitcher-shaped corolla with a
broad middle part, e.g., Bryophyllum, Petrospora.
Rotate: Regular, gamopetalous, wheel-shaped
corolla with a narrow and short corolla tube, and the limbs of petals being at
a right angle to the tube, e.g., Nyctanthes.
Butterfly-like or papilionaceous: It is an irregular, polypetalous
corolla with its five petals arranged so as to resemble a butterfly. It
consists of a posterior largest ‘vexillurri, two lateral ‘alae,’ and two
anterior fused petals called ‘keel,’ as in members of Papilionaceae.
Ligulate: It is a strap-shaped, zygomorphic,
gamopetalous corolla with a short, narrow tube and strap-like, flat upper
portion, e.g., ray florets of Compositae.
Bilipped or Bilabiate: Zygomorphic,
gamopetalous corolla, in which petals are so fused together that they appear to
be divided into two separate lips, e.g., Adhatoda, Ocimum.
Personate or Masked: It is also a bilabiate corolla, but
here the mouth of the corolla is closed because two lips are very close to each
other, e.g., Linaria.
-Corolla appendages
Sometimes the corolla or perianth is
provided with external growths. In the "Antirrhinum majus,"
the corolla tube extends laterally, forming a pouch-like appendage known as the
"Gibbous" (Figure 5b). In the "Balsam," "Garden
nasturtiums (Tropaeolum majus)," "Prunus," and "Orchids,"
the perianth extends in the form of a tube known as the spur. Hence, the
corolla is known as the spur-like or spur-like corolla (Figure 6a). Sometimes,
when the corolla is split transversely, an additional crown-like or ring-like
structure develops from the corolla or the stamens, sometimes appearing on the
inner wall of the throat. It consists of lobes, scales, or loose or fused hairs
known as the corona. The corona may be distinct, as in the passionflower,
oleander (Figure 6b), and dodder (Cuscuta). In the daffodil (Narcissus), there
is a beautiful, cup-like corona that adds to the flower's beauty and plays a
key role in attracting pollinating insects (Figure 6c).
Aestivation: Aestivation is the arrangement of
either the sepals or the petals in a flower bud with relation to one another,
as vernation proper is the arrangement of young leaves in the vegetative bud.
Aestivation is of considerable
importance in the classification of plants. This may be of the following types:
Floral Leaves in One Whorl:
- Valvate:
Floral leaves in a whorl may just
touch one another at the margins without overlapping, as seen in the family
Anonaceae or the subfamily Mimoseae.
- Contorted or twisted:
When overlapping is regular in one
direction so that one margin overlaps the next member on one side while its
other margin is overlapped by the one before, giving a twisted appearance to
the bud.
This is seen in Malvaceae (China
rose, cotton, etc.) and Apocynaceae (Nerium, Thevetia, etc.).
Floral Leaves Not in One Whorl:
- Imbricate:
When the margins overlap one another
but not in any particular order, as in the subfamily Caesalpinieae. In
imbricate flowers the petals do not actually lie in a single whorl.
- Quincuncial:
The floral leaves are not in a whorl
but spirally arranged. Leaves 1 and 2 are external, 3 is partly external, and 4
and 5 are internal. This is seen in guava (Psidium guyava of Myrtaceae), etc.
- Vexillary:
This is the typical aestivation of
the papilionaceous corolla. The posterior vexillum overlaps the two alae, which
again overlap the paired anterior carina.
Perianth:
In most monocotyledons the calyx and
the corolla are not differentiated, and the general accessory whorls form the
perianth, as seen in Polyanthes, Crinum, etc. This structure plays a crucial
role in the reproductive success of these plants by providing protection and
support for the developing flowers. Additionally, the arrangement of floral
parts can influence pollinator behavior, thereby affecting the plant's ability
to reproduce effectively. The perianth is often brightly colored or petaloid,
as in Gloriosa superba (Liliaceae), Crinum asiaticum
(Amaryllidaceae), etc. The perianth in some members of Amaranthaceae is
membranous and persistent. In Graminaceae the perianth is represented by two
lodicules, as seen in Festuca.
If the perianth members are free from
one another, as in Gloriosa superba, the perianth is termed
polyphyllous. This characteristic can enhance the attraction of specific
pollinators, leading to more effective cross-pollination. Understanding these
variations in floral structure is crucial for conservation efforts and
agricultural practices aimed at improving plant reproduction and biodiversity.
When the perianth members are united, as in Polyanthes tuberosa, the perianth
is gamophyllous.
References
Downie S, Robertson
K. 2016. "Digital Flowers: Floral Formulas". University of
Illinois.
Eames AJ. 1961.
Morphology of the Angiosperms. New York: McGraw-Hill Book Co.
Greyson RI.1994. The
Development of Flowers. Oxford University Press.
Leins P, Erbar C.2010.
Flower and Fruit. Stuttgart: Schweizerbart Science Publishers. .
Prenner G. 2010. "Floral formulae updated for
routine inclusion in formal
taxonomic descriptions".
Taxon. 59: 241-250.
Sattler R. 1973.
Organogenesis of Flowers. A Photographic Text-Atlas. University of Toronto Press
SattlerR.1978.
"'Fusion' and 'continuity' in floral morphology". Notes of the Royal
Botanic Garden, Edinburgh.
36: 397-405.
Sharma OP. 2009. Plant Taxonomy (2nd ed.). Tata McGraw-Hill Education. pp. 165-166.
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