BiologyCBSE Class 11 · Morphology of Flowering Plants

Floral Parts: Aestivation, Androecium, Gynoecium and Placentation

Updated 17 October 2026 · Fact-checked

A flower has four whorls: calyx, corolla, androecium and gynoecium. Aestivation is the arrangement of petals or sepals in the bud (valvate, twisted, imbricate, vexillary). Stamens may be free, fused (monadelphous, diadelphous, polyadelphous) or attached to petals (epipetalous). Carpels may be apocarpous or syncarpous. Placentation is marginal, axile, parietal, free central or basal.

Notice the four whorls from outside in: calyx, corolla, androecium, then gynoecium at the centre, where ovules sit inside the ovary.

Illustration drawn for QuestionBuddy.

Understand Floral Parts, Aestivation and Placentation

Whorls of the flower. Calyx (sepals), corolla (petals), androecium (stamens) and gynoecium (carpels). Flowers may be complete (all four whorls) or incomplete; bisexual or unisexual.

Aestivation (arrangement of sepals or petals in the floral bud):

Valvate: edges just touch without overlapping (*Calotropis*).
Twisted: one margin overlaps the next in a regular direction (China rose, lady's finger, cotton).
Imbricate: margins overlap irregularly, with no definite direction (*Cassia*, gulmohur).
Vexillary: the largest petal (standard) overlaps the two lateral petals (wings), which in turn overlap the two smallest anterior petals (keel): pea and bean flowers.

Androecium. Made of stamens (filament and anther; the anther has pollen sacs where pollen forms). Stamens may be:

Epipetalous: attached to the petals (brinjal).
Epiphyllous: attached to the perianth (lily).
Monadelphous: filaments united in one bunch (China rose), diadelphous: two bundles (pea), polyadelphous: more than two bundles (citrus).
Anthers may be of equal or unequal length.

Gynoecium. Made of one or more carpels (stigma, style, ovary). Apocarpous: carpels free (lotus, rose). Syncarpous: carpels fused (mustard, tomato). Each ovary has one or more ovules attached to the placenta.

Position of ovary (and floral parts).

Hypogynous: ovary superior, other parts below it (mustard, China rose, brinjal).
Perigynous: ovary half-inferior, other parts at the same level at the rim of the thalamus (plum, rose, peach).
Epigynous: ovary inferior, other parts above it (guava, cucumber, ray florets of sunflower).

Placentation (arrangement of ovules within the ovary):

Marginal: placenta along the ventral suture of a one-chambered ovary, ovules in two rows (pea).
Axile: placenta in the axis of a multi-chambered ovary (China rose, tomato, lemon).
Parietal: ovules on the inner wall of a one-chambered ovary (mustard, *Argemone*).
Free central: ovules borne on the central axis without septa (*Dianthus*, primrose).
Basal: placenta at the base of the ovary with a single ovule (sunflower, marigold).

Floral formula and diagrams use symbols: Br (bracteate), K (calyx), C (corolla), P (perianth), A (androecium), G (gynoecium; G-bar inferior, G with underline superior), ⊕ actinomorphic, % zygomorphic.

Draw and label: transverse section of an ovary showing axile placentation. Checklist: locules, septa, central axis with ovules, ovary wall.

Floral Parts, Aestivation and Placentation: key facts

Aestivation: Valvate Calotropis
Twisted China rose, cotton
Imbricate Cassia
Vexillary pea; Bud arrangement
Stamen union: Monadelphous one bundle (China rose)
Diadelphous two (pea)
Polyadelphous many (citrus); Androecium
Ovary position: $H y p o g y n o u s : s u p er i or ∣ P er i g y n o u s : ha l f - in f er i or ∣ E p i g y n o u s : in f er i or$; Examples: mustard, rose, guava
Placentation: Marginal pea
Axile tomato
Parietal mustard
Free central Dianthus
Basal sunflower; Ovule arrangement

Valvate	Calotropis
Twisted	China rose, cotton
Imbricate	Cassia
Vexillary	pea

Monadelphous	one bundle (China rose)
Diadelphous	two (pea)
Polyadelphous	many (citrus)

Marginal	pea
Axile	tomato
Parietal	mustard
Free central	Dianthus
Basal	sunflower

How to answer Floral Parts, Aestivation and Placentation questions

Questions give a flower or description and ask for the type.

1Count loci and look at placental position to decide placentation.
2For aestivation, check overlapping direction.
3For stamens, count bundles.
4For ovary position, compare the level of the ovary with petals and sepals.
5Give an example for every type.

Floral Parts, Aestivation and Placentation in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Vegetable market

Suppose a market has pea pods, tomatoes and mustard siliquae, and a student wants to explain why the seeds sit differently in each.

Name the placentation in each and relate it to the number of chambers.

Try it first, then show the solutionSolution

Pea pod: marginal placentation, one chamber, seeds along the suture.
Tomato: axile placentation, multi-chambered, seeds on the central axis.
Mustard: parietal placentation, a single chamber that later forms two by a false septum, seeds on the wall.

Answer: Marginal (pea), axile (tomato), parietal (mustard).

Memory hook: Pea suture, tomato axis, mustard wall.

Tricks to remember Floral Parts, Aestivation and Placentation

Short memory aids. Say each one aloud once, then use it on a question the same day.

VTIV
Valvate, Twisted, Imbricate, Vexillary.
Use it when: Aestivation
MAP-FB
Marginal, Axile, Parietal, Free central, Basal.
Use it when: Placentation
Hypo, Peri, Epi
Superior, middle, inferior ovary.
Use it when: Ovary position

Floral Parts, Aestivation and Placentation: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Aestivation · 2 marks · Very short answerBoard level

Describe the arrangement of petals in the bud of a bean flower and of a Cassia flower, naming each type of aestivation.

Try it first, then show the solutionSolution

Bean: the largest petal overlaps two lateral petals which overlap the two smallest, so vexillary (1 mark).
Cassia: margins overlap irregularly with no fixed direction, so imbricate (1 mark).

Answer: Bean vexillary; Cassia imbricate.

Example 2: Placentation types · 2 marks · Very short answerBoard level

Name the placentation described: (a) seeds in a pod, in two rows along one edge (b) a single seed at the base of the fruit, as in a sunflower fruit (c) a three-chambered ovary with ovules on the axis where the walls meet. Give a plant for each.

Try it first, then show the solutionSolution

(a) Marginal, pea; (b) basal, sunflower (1 mark).
(c) Axile, tomato or China rose (1 mark).

Answer: Marginal (pea); basal (sunflower); axile (tomato).

Example 3: Staminal union · 3 marks · Short answerHarder board level

Distinguish monadelphous, diadelphous and polyadelphous stamens with examples.

Try it first, then show the solutionSolution

Monadelphous: filaments united in one bundle, as in China rose (1 mark).
Diadelphous: two bundles, as in pea (1 mark).
Polyadelphous: more than two bundles, as in citrus (1 mark).

Answer: One, two or many bundles.

Example 4: Ovary position · 3 marks · Short answerHarder board level

Pistil in a cucumber flower sits below the sepals, petals and stamens, while in China rose it sits above them. Name the two conditions, and the third one between them, with an example of each.

Try it first, then show the solutionSolution

Cucumber: epigynous, ovary inferior (1 mark).
China rose: hypogynous, ovary superior (1 mark).
In between is perigynous, ovary half inferior with other parts at the same level, as in rose or plum (1 mark).

Answer: Epigynous, hypogynous, perigynous.

Example 5: Reading a fruit · 4 marks · Short answerHOTS / competency

A cut ovary shows three chambers, with ovules attached to a central pillar where the walls meet. Identify placentation, give an example, explain how it differs from free central, and say how many placentae could be seen.

Try it first, then show the solutionSolution

Axile placentation (1 mark).
Example: tomato or China rose (1 mark).
Free central has a single chamber without septa, so the ovules sit on a central axis; axile has septa and chambers (1 mark).
Three chambers give three placentae at the axis (1 mark).

Answer: Axile; chambers present; three placentae.

Where students lose marks in Floral Parts, Aestivation and Placentation

The slips examiners see most often, and what to write instead.

Mistake: Imbricate for pea
Vexillary forgotten.
Wrong working
Pea aestivation is imbricate.
Right working
Pea is vexillary.
Do this: Standard, wings, keel.
Usually costs: 1 mark.
Mistake: Axile in mustard
Chambers confused.
Wrong working
Mustard has axile placentation.
Right working
Mustard has parietal placentation.
Do this: One chamber = parietal.
Usually costs: 1 mark.
Mistake: Perigynous equals inferior
Position mixed.
Wrong working
Perigynous ovary is inferior.
Right working
Perigynous ovary is half-inferior.
Do this: Epigynous is inferior.
Usually costs: 1 mark.

Exam tips

Learn one example for each type.
Draw a quick sketch of placentation types.
State the number of chambers in placentation answers.
Use consistent terms for the position of the ovary.

Practice questions on Floral Parts, Aestivation and Placentation

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The largest petal overlapping the two lateral petals in the bud is seen in
(a) Calotropis (b) cotton (c) bean (d) Cassia
Hint
Standard, wings, keel.
Answer
(c).
Q2 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Parietal placentation occurs in a one-chambered ovary.
Reason (R): Ovules are borne on the inner wall of the ovary.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Wall placenta.
Answer
(a).
Q3 · 2 marks · Very short answerHarder board level
What is epipetalous? Give a plant. How does it differ from epiphyllous?
Hint
Where are stamens attached?
Answer
Stamens attached to petals, as in brinjal; epiphyllous stamens are attached to the perianth, as in lily.
Q4 · 4 marks · Case-basedHarder board level
Read and answer.
Suppose a flower has five petals in which the largest overlaps two side petals that overlap the two smallest, ten stamens in two bundles (9+1), and a one-chambered ovary with ovules in two rows along one suture.
(a) Name the type of aestivation. (1)
(b) Name the stamen union. (1)
(c) Name the placentation. (1)
(d) Name the likely family character and flower. (1)
Hint
Pea type, with one exception.
Answer
(a) Vexillary. (b) Diadelphous. (c) Marginal. (d) A pea-like flower of the legume family (Fabaceae).
Q5 · 3 marks · Short answerHOTS / competency
Suppose a student claims all syncarpous ovaries have axile placentation. Disprove the claim with an example and explain how syncarpous differs from apocarpous.
Hint
Mustard is syncarpous.
Answer
Mustard has fused carpels (syncarpous) with parietal placentation, so the claim fails. Syncarpous carpels are fused; apocarpous carpels are free (lotus, rose).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Placentation in pea?Show answer
Marginal.
2.Placentation in sunflower?Show answer
Basal.
3.Which flower is diadelphous?Show answer
Pea.
4.Ovary position in guava?Show answer
Inferior (epigynous).
5.Apocarpous example?Show answer
Lotus.
6.Vexillary parts?Show answer
Standard, wings, keel.

Floral Parts, Aestivation and Placentation: frequently asked questions

What is aestivation?

Arrangement of sepals or petals in the bud.

What is placentation?

Arrangement of ovules within the ovary.

What is a carpel?

Unit of gynoecium: stigma, style and ovary.

What is the androecium?

The whorl of stamens.

What is epigynous?

A flower with an inferior ovary.