BiologyISC Class 11 · Morphology of Flowering Plants

The Flower: Whorls, Aestivation, Androecium, Gynoecium and Inflorescence

Updated 17 October 2026 · Fact-checked

A typical flower has four whorls: calyx, corolla, androecium and gynoecium. Flowers are classified by symmetry, position of the ovary and number of floral parts; aestivation, stamen cohesion and placentation have defined types. The inflorescence is racemose (unlimited growth) or cymose (limited growth).

Understand Flower, Inflorescence and Floral Formula

Flower. A modified shoot bearing four whorls: calyx (sepals), corolla (petals), androecium (stamens, the male part) and gynoecium (carpels, the female part). *Symmetry:* actinomorphic (radial, as in mustard) or zygomorphic (bilateral, as in pea). *Merism:* trimerous (monocots), tetramerous, pentamerous (dicots). *Position of the ovary:* hypogynous (superior ovary, other parts below it: mustard, China rose, brinjal); perigynous (ovary half-inferior: plum, rose, peach); epigynous (inferior ovary: guava, cucumber, sunflower ray florets).

Aestivation. The arrangement of sepals or petals in the bud: valvate (just touching: Calotropis), twisted (overlapping one side: China rose), imbricate (irregular overlap: Cassia), and vexillary (in pea: standard, wings and keel).

Androecium. Stamens have filament and anther. Cohesion: monadelphous (filaments united in one bundle: China rose), diadelphous (two bundles: pea), polyadelphous (many bundles: citrus). Epipetalous means stamens attached to petals (brinjal), and epiphyllous to perianth.

Gynoecium. Carpels have stigma, style and ovary. Apocarpous (free carpels: lotus, rose) or syncarpous (fused carpels: mustard, tomato). *Placentation* is the arrangement of ovules within the ovary: marginal (pea), axile (China rose, tomato, lemon), parietal (mustard, Argemone), free central (Dianthus, Primrose) and basal (sunflower, marigold).

Inflorescence. In racemose types the main axis keeps growing and flowers open in acropetal succession (older at the base). In cymose types the main axis ends in a flower and growth is limited; flowers open in basipetal succession.

Floral formula. Symbols: Br (bracteate), % (zygomorphic), ⊕ (actinomorphic), ⚥ (bisexual), K calyx, C corolla, P perianth, A androecium, G gynoecium (underlined G̲ for a superior ovary; Ḡ for an inferior ovary). Examples: Fabaceae: % ⚥ K(5) C1+2+(2) A(9)+1 G̲1; Solanaceae: ⊕ ⚥ K(5) C(5) A5 G̲(2); Liliaceae: ⊕ ⚥ P(3+3) A3+3 G̲(3).

Flower, Inflorescence and Floral Formula: key facts

Whorls: $C a l y x ∣ C or o l l a ∣ A n d r oec i u m ∣ G y n oec i u m$; Essential whorls: androecium and gynoecium.
Ovary position: $H y p o g y n o u s : s u p er i or ∣ P er i g y n o u s : ha l f - in f er i or ∣ E p i g y n o u s : in f er i or$; Mustard | plum | guava.
Placentation: Marginal pea
Axile China rose
Parietal mustard
Free central Dianthus
Basal sunflower; Position of ovules in the ovary.
Floral formula (Solanaceae): $\oplus ⚥ K (5) C (5) A 5 G (2) w i t h G u n d er l in e d$; Superior ovary; bracket means united.

Marginal	pea
Axile	China rose
Parietal	mustard
Free central	Dianthus
Basal	sunflower

Flower, Inflorescence and Floral Formula 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.

Describing a pea flower for a herbarium sheet

Suppose a student describes a pea flower: bilaterally symmetrical, bisexual, five united sepals, five petals in three kinds, ten stamens in two bundles, and one carpel with a superior ovary.

Write its floral formula and name the aestivation and placentation.

Try it first, then show the solutionSolution

Symmetry % ; bisexual ⚥ ; calyx K(5); corolla C1+2+(2), that is one standard, two wings and two joined keel petals.
Stamens A(9)+1 (diadelphous); gynoecium G̲1 (superior ovary).
Aestivation vexillary; placentation marginal.

Answer: % ⚥ K(5) C1+2+(2) A(9)+1 G̲1; vexillary; marginal.

Memory hook: Brackets show fusion; + separates groups.

Tricks to remember Flower, Inflorescence and Floral Formula

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

Acropetal: racemose, basipetal: cymose
Racemose flowers open from the base upward; cymose flowers open from the top downward.
Use it when: Inflorescence questions.
Pea-marginal, mustard-parietal
Learn one plant for each placentation type.
Use it when: Placentation matching.

Flower, Inflorescence and Floral Formula: solved examples

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

Example 1: Placentation in mustard · 1 mark · MCQBoard level

The placentation in mustard is:
(a) marginal
(b) axile
(c) parietal
(d) basal

Try it first, then show the solutionSolution

Mustard has a parietal placentation.

Answer: (c) parietal

Example 2: Whorls of a flower · 3 marks · Short answerBoard level

Name the four whorls of a typical flower and state which are essential and which are accessory.

Try it first, then show the solutionSolution

Calyx (sepals), corolla (petals), androecium (stamens), gynoecium (carpels). (1.5 marks)
Androecium and gynoecium are essential (reproductive) whorls. (0.75 mark)
Calyx and corolla are accessory (protective and attractive) whorls. (0.75 mark)

Answer: Calyx, corolla, androecium, gynoecium; androecium and gynoecium are essential.

Example 3: Aestivation and cohesion · 4 marks · Short answerHarder board level

Give an example for each: valvate and twisted aestivation; monadelphous and diadelphous stamens; apocarpous and syncarpous gynoecium.

Try it first, then show the solutionSolution

Valvate: Calotropis; twisted: China rose. (1.3 marks)
Monadelphous: China rose; diadelphous: pea. (1.3 marks)
Apocarpous: lotus or rose; syncarpous: mustard or tomato. (1.4 marks)

Answer: Calotropis, China rose; China rose, pea; lotus, mustard.

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

Differentiate between hypogynous, perigynous and epigynous flowers with an example each and say which has an inferior ovary.

Try it first, then show the solutionSolution

Hypogynous: gynoecium highest, ovary superior (mustard, China rose, brinjal). (1 mark)
Perigynous: ovary half-inferior, other parts on the rim at the same level (plum, rose, peach). (1 mark)
Epigynous: other floral parts above the ovary, ovary inferior (guava, cucumber). (1 mark)

Answer: Epigynous flowers have an inferior ovary.

Example 5: Inflorescence and formula · 5 marks · Long answerHOTS / competency

Compare racemose and cymose inflorescences. Write the floral formula of a brinjal flower (actinomorphic, bisexual, five united sepals, five united petals, five epipetalous stamens, two united carpels with a superior ovary).

Try it first, then show the solutionSolution

Racemose: main axis continues to grow; flowers arranged acropetally (youngest at the tip). (1.5 marks)
Cymose: main axis ends in a flower; limited growth; flowers basipetal (youngest at the base). (1.5 marks)
Floral formula: ⊕ ⚥ K(5) C(5) A5 G̲(2). (1 mark)
Meaning: actinomorphic, bisexual, united calyx and corolla, five free stamens (epipetalous), and a bicarpellary syncarpous gynoecium with a superior ovary. (1 mark)

Answer: Racemose: acropetal; cymose: basipetal; ⊕ ⚥ K(5) C(5) A5 G̲(2).

Where students lose marks in Flower, Inflorescence and Floral Formula

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

Mistake: Mixing the ovary positions
Writing guava as hypogynous.
Do this: Guava is epigynous (inferior ovary).
Usually costs: 1 mark.
Mistake: Writing the formula without symbols
Leaving out the underline for a superior ovary.
Do this: Underline G for a superior ovary; draw a line above G for inferior.
Usually costs: 1 mark.
Mistake: Reversing acropetal and basipetal
Saying racemose flowers open from the tip.
Do this: Racemose: acropetal (bottom to top); cymose: basipetal.
Usually costs: 1 mark.

Exam tips

Draw a labelled diagram of a flower with the four whorls.
Give one plant example for each aestivation and placentation type.
Explain the brackets and the plus sign in floral formulae.
Compare racemose and cymose in two or three points.

Practice questions on Flower, Inflorescence and Floral Formula

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
Vexillary aestivation is found in:
(a) pea
(b) mustard
(c) Calotropis
(d) China rose
Hint
Standard, wings and keel.
Answer
(a) pea
Q2 · 2 marks · Short answerBoard level
What is placentation? Name any two types with an example each.
Hint
It is about ovules in the ovary.
Answer
Placentation is the arrangement of ovules within the ovary. Marginal in pea; axile in China rose; parietal in mustard.
Q3 · 3 marks · Short answerHarder board level
Differentiate between actinomorphic and zygomorphic flowers with examples.
Hint
Think of the planes of symmetry.
Answer
Actinomorphic: can be divided into two equal halves by any radial plane (mustard, datura). Zygomorphic: only one plane gives two equal halves (pea, Cassia).
Q4 · 3 marks · Short answerHarder board level
Give the meaning of the symbols in the formula % ⚥ K(5) C1+2+(2) A(9)+1 G̲1.
Hint
Symmetry, sex, whorls.
Answer
% zygomorphic, ⚥ bisexual; K(5) five united sepals; C1+2+(2) one standard, two wings and two fused keel petals; A(9)+1 diadelphous stamens; G̲1 one carpel with a superior ovary.
Q5 · 3 marks · Assertion-reasonHarder board level
Assertion (A): Guava has an epigynous flower. Reason (R): The ovary lies below the other floral parts. Choose: (a) both true and R explains A (b) both true, R does not explain A (c) A true, R false (d) A false, R true.
Hint
Define epigyny.
Answer
(a) Both are true and R explains A.
Q6 · 4 marks · Case-basedHOTS / competency
Case study: Suppose a student studies a sunflower head and a pea flower.
(i) Name the placentation in sunflower. (1 mark)
(ii) Name the aestivation of the pea corolla. (1 mark)
(iii) State the type of stamens in pea. (1 mark)
(iv) State the type of inflorescence in sunflower (capitulum) as racemose or cymose. (1 mark)
Hint
Recall the examples.
Answer
(i) Basal. (ii) Vexillary. (iii) Diadelphous (9 + 1). (iv) Racemose.

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.Male part of a flower?Show answer
Androecium.
2.Placentation in pea?Show answer
Marginal.
3.Stamens of China rose?Show answer
Monadelphous.
4.Opening of cymose flowers?Show answer
Basipetal.

Flower, Inflorescence and Floral Formula: frequently asked questions

What does bisexual mean in a flower?

The flower has both stamens and carpels.

What is the difference between apocarpous and syncarpous?

In an apocarpous gynoecium the carpels are free; in a syncarpous gynoecium they are fused.

What is epipetalous?

Stamens attached to the petals, as in brinjal.