Tamil Nadu Board of Secondary EducationHSC Science Class 11th
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Parts of Flower - Accessory Organs

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  • Accessory organs
  1. Arrangement of whorls
  2. Calyx
  3. Corolla
  4. Perianth
  5. Aestivation


Accessory organs:

1) Arrangement of whorls:

The position of perianth (sepals, petals, tepals) parts relative to one another is called perianth arrangement.

  1. Cyclic or whorled: All the floral parts are arranged in definite whorls. Example: Brassica.
  2. Acyclic or spiral: The floral parts are arranged in spirals on the elongated fleshy torus. Example: Magnolia.
  3. Spirocyclic or hemicyclic: Some parts are in whorls and others parts are in spirals. Example: Annona, Polyalthia.

2) Calyx:

Calyx protects the flower in bud stage. Outermost whorl of flower is calyx. Unit of the calyx is sepal. Normally green in colour.

  1. Fusion:
    a) Aposepalous (polysepalous):
    The flower with distinct sepals. Example: Brassica, Annona.
    b) Synsepalous: The flower with united or fused sepals. Example: Hibiscus.

  2. Duration of floral parts:
    a) Caducous or fugacious calyx:
    Calyx that withers or falls off during the early development stage of flower. Example: Papaver.

    Caducous bud with sepal

    Caducous flower without sepal

    b) Deciduous: Calyx that falls soon after the opening of flower (anthesis) Example: Nelumbo.


    c) Persistant: Calyx that persists and continues to be along with the fruit and forms a cup at the base of the fruit. Example: Brinjal.

    Persistant calyx
    d) Accrescent: Calyx that is persistent, grows along with the fruit and encloses the fruit either completely or partially. Example: Physalis.


  • Shapes of calyx:
  1. The bell-shaped calyx is called Campanulate.
  2. The fruiting calyx is urn-shaped in Withania and it is called urceolate.
  3. In Datura calyx is tube-like and it is known as tubular. the two-lipped calyx is present in Ocimum.
  4. Sometimes calyx is coloured and called petaloid. Example: Saraca and Mussanda.
  5. In Tridax, the calyx is modified into hair-like structures called pappus.




3) Corolla:

Corolla is the most attractive part in majority of the flowers and is usually brightly coloured. Corolla helps to display the flower and attracts pollinators.
1) Fusion:

  1. Apopetalous (polypetalous): Petals are distinct. Example: ­Hibiscus.
  2. Sympetalous (gamopetalous): Petals are fused. Example: D­atura.

4) Perianth:

  • Undifferentiated calyx and corolla in a flower are called perianth.
  • Each member is called a tepal.
  • If the tepals are distinct they are called Apotepalous (Polyphyllous). Example: Allium sativum.
  • Fused tepals are called Syntepalous (Gamophyllous). Example: Allium cepa.
  • Lodicule: Reduced scale-like perianth in the members of Poaceae is called lodicule.

5) Aestivation:

The arrangement of sepals and petals in the flower bud is said to be aestivation.

i. Valvate

ii. Twisted

iii. Imbricate

iv. Quincuncial

v. Vexillary

  1. Valvate: Margins of sepals or petals do not overlap but just touch each other. Example: Calyx in members of Malvaceae, Calotropis, Annona.
  2. Twisted or Convolute or Contorted: One margin of each petal or sepal overlapping on the other petal. Example: Petals of China rose.
  3. Imbricate: Sepals and petals irregularly overlap on each other; one member of the whorl is exterior, one interior and the rest of the three having one margin exterior and other interior. Example: Cassia, Delonix.
    There are 3 types: 1. Ascendingly imbricate; 2. Quincuncial; 3. Vexillary.
  4. Vexillary: Large posterior petals both margins overlap lateral petals. Lateral petals other margin overlaps anterior petals. Example: Pea, Bean.
  5. Quincuncial: It is a type of imbricate aestivation in which two petals are external and two internal and one petal with one margin internal and the other margin external. Example: Guava, Calyx of Ipomoea, Catharanthus.
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