The Flower
The flower is a modified shoot and the reproductive unit of angiosperms. This page on the flower covers racemose and cymose inflorescences, the four floral whorls, symmetry and the position of the ovary. It then explains aestivation, the androecium, the gynoecium and the five types of placentation, with examples, in the NCERT order. NEET often tests these flower terms with their examples, mostly as match-the-list and statement questions.
- ★ Must learn A flower is a modified shoot: the shoot apical meristem becomes a floral meristem.
- ★ Must learn Racemose: axis keeps growing, flowers in acropetal succession. Cymose: axis ends in a flower, flowers in basipetal order.
- Four whorls on the thalamus: calyx and corolla (accessory), androecium and gynoecium (reproductive).
- Actinomorphic: mustard, datura, chilli. Zygomorphic: pea, gulmohur, bean, Cassia. Asymmetric: canna.
- ★ Must learn Ovary superior in hypogynous, half inferior in perigynous, inferior in epigynous flowers.
- ★ Must learn Aestivation: valvate (Calotropis), twisted (china rose, lady's finger, cotton), imbricate (Cassia, gulmohur), vexillary (pea, bean).
- Stamens: epipetalous (brinjal), epiphyllous (lily); monoadelphous (china rose), diadelphous (pea), polyadelphous (citrus).
- A carpel has stigma, style and ovary; apocarpous (lotus, rose) or syncarpous (mustard, tomato).
- ★ Must learn Placentation: marginal (pea), axile (china rose, tomato, lemon), parietal (mustard, Argemone), free central (Dianthus, primrose), basal (sunflower, marigold).
- After fertilisation, ovules develop into seeds and the ovary into a fruit.
1. The Flower as a Modified Shoot
- The shoot apical meristem changes into a floral meristem.
- The internodes do not elongate, so the axis gets condensed.
- At successive nodes, the apex produces different kinds of floral appendages laterally, instead of leaves.
- ★ Exam imp When a shoot tip transforms into a flower, the flower is always solitary.
2. Inflorescence
- Inflorescence: the arrangement of flowers on the floral axis.
- Two major types are defined by whether the apex develops into a flower or continues to grow: racemose and cymose.
2.1 Racemose inflorescence
- ★ Exam imp The main axis continues to grow.
- Flowers are borne laterally in acropetal succession: older flowers at the base, younger flowers towards the apex.
2.2 Cymose inflorescence
- ★ Exam imp The main axis terminates in a flower, so its growth is limited.
- Flowers are borne in basipetal order: the oldest flower at the tip of the axis, younger flowers lower down.
| Feature | Racemose | Cymose |
|---|---|---|
| Main axis | Continues to grow | Terminates in a flower |
| Growth of axis | Unlimited | Limited |
| Order of flowers | Acropetal succession | Basipetal order |
| Oldest flower | At the base | At the tip |
Racemose Rises; Cyme Caps. In a raceme, the axis keeps rising and new flowers open towards the top (acropetal). In a cyme, a flower caps the axis, so new flowers come below it (basipetal).
- Acropetal = racemose; basipetal = cymose. NEET swaps these pairs in statement questions.
- The basis of the two types is whether the apex develops into a flower or continues to grow.
3. The Flower and its Whorls
- The flower is the reproductive unit in angiosperms; it is meant for sexual reproduction.
- ★ Exam imp A typical flower has four whorls on the swollen end of the stalk (pedicel), called the thalamus or receptacle.
- The whorls are calyx, corolla, androecium and gynoecium.
- Calyx and corolla are accessory organs.
- Androecium and gynoecium are reproductive organs.
- In some flowers, like lily, the calyx and corolla are not distinct; together they are called the perianth.
- Bisexual flower: has both androecium and gynoecium.
- Unisexual flower: has either only stamens or only carpels.
Whorls from outside to inside: "Can Cats Annoy Grandma?" = Calyx, Corolla, Androecium, Gynoecium. The first two Cs are accessory; A and G are reproductive.
4. Symmetry, Merosity and Bracts
| Symmetry | Definition | Examples |
|---|---|---|
| Actinomorphic (radial symmetry) | Can be divided into two equal radial halves in any radial plane passing through the centre | Mustard, datura, chilli |
| Zygomorphic (bilateral symmetry) | Can be divided into two similar halves only in one particular vertical plane | Pea, gulmohur, bean, Cassia |
| Asymmetric (irregular) | Cannot be divided into two similar halves by any vertical plane passing through the centre | Canna |
- Trimerous, tetramerous, pentamerous: floral appendages in multiples of 3, 4 or 5, respectively.
- Bract: a reduced leaf found at the base of the pedicel.
- Bracteate flowers have bracts; ebracteate flowers have none.
Zygomorphic = Peas Grow Beside Cassia: Pea, Gulmohur, Bean, Cassia. Actinomorphic = M-D-C: Mustard, Datura, Chilli. Asymmetric: Canna cannot be halved.
5. Position of Floral Parts on the Thalamus
Flowers are described by the position of the calyx, corolla and androecium with respect to the ovary on the thalamus.
| Type | Arrangement | Ovary | Examples |
|---|---|---|---|
| Hypogynous | Gynoecium occupies the highest position; other parts lie below it | Superior | Mustard, china rose, brinjal |
| Perigynous | Gynoecium in the centre; other parts on the rim of the thalamus, almost at the same level | Half inferior | Plum, rose, peach |
| Epigynous | Margin of the thalamus grows upward, encloses the ovary completely and fuses with it; other parts arise above the ovary | Inferior | Guava, cucumber, ray florets of sunflower |
★ Very important Hypogynous = superior ovary; perigynous = half inferior; epigynous = inferior ovary. In epigynous flowers, the thalamus encloses and fuses with the ovary.
Hypo = below: the other parts sit below the ovary, so the ovary is on top (superior). Epi = upon: the other parts arise upon the ovary, so it is inferior. Peri = around: they sit around it on the rim. Perigynous examples are Plum, Peach and rose; epigynous examples are G-C-S: Guava, Cucumber, Sunflower ray florets.
What is a bract?
Name the flowers with an inferior ovary given in this topic.
Which flower is asymmetric?
What is a perianth?
6. Parts of a Flower: Calyx and Corolla
Each flower normally has four floral whorls: calyx, corolla, androecium and gynoecium.
6.1 Calyx
- The calyx is the outermost whorl; its members are sepals.
- Sepals are generally green and leaf-like; they protect the flower in the bud stage.
- Gamosepalous: sepals united. Polysepalous: sepals free.
6.2 Corolla
- The corolla is composed of petals.
- Petals are usually brightly coloured to attract insects for pollination.
- Gamopetalous: petals united. Polypetalous: petals free.
- The shape and colour of the corolla vary greatly; it may be tubular, bell-shaped, funnel-shaped or wheel-shaped.
6.3 Aestivation
- ★ Exam imp Aestivation: the mode of arrangement of sepals or petals in the floral bud with respect to the other members of the same whorl.
- The main types are valvate, twisted, imbricate and vexillary.
| Type | Arrangement of margins | Examples |
|---|---|---|
| Valvate | Just touch one another at the margin, without overlapping | Calotropis |
| Twisted | One margin overlaps that of the next one, and so on | China rose, lady's finger, cotton |
| Imbricate | Margins overlap one another, but not in any particular direction | Cassia, gulmohur |
| Vexillary (papilionaceous) | Standard overlaps the wings, which overlap the keel | Pea, bean |
In vexillary aestivation there are five petals, overlapping from outside inwards:
- Standard: the largest petal; it overlaps the two wings.
- Wings: the two lateral petals; they overlap the keel.
- Keel: the two smallest, anterior petals, innermost.
Examples in order: V-T-I-V = Calotropis, China rose, Cassia, Pea. Twisted also covers lady's finger and cotton; imbricate also covers gulmohur; vexillary also covers bean. Vexillary petals: 1 + 2 + 2 = standard, wings, keel.
Reading a bud figure: if no petals overlap, it is valvate. If every petal overlaps the next in the same direction, it is twisted. If one petal is fully outside and one fully inside, it is imbricate. If one large outer petal covers four smaller ones, it is vexillary.
7. Androecium
- The androecium is composed of stamens.
- Each stamen represents the male reproductive organ.
- A stamen has a stalk, the filament, and an anther.
- ★ Exam imp Each anther is usually bilobed, and each lobe has two chambers, the pollen-sacs.
- Pollen grains are produced in the pollen-sacs.
- Staminode: a sterile stamen.
- Stamens may be united with other members, such as petals, or among themselves.
- There may be variation in the length of filaments within a flower, as in Salvia and mustard.
| Condition | Meaning | Example |
|---|---|---|
| Epipetalous | Stamens attached to the petals | Brinjal |
| Epiphyllous | Stamens attached to the perianth | Lily |
| Polyandrous | Stamens free | - |
| Monoadelphous | Stamens united into one bunch or bundle | China rose |
| Diadelphous | Stamens united into two bundles | Pea |
| Polyadelphous | Stamens united into more than two bundles | Citrus |
★ Very important An anther is usually bilobed with two pollen-sacs in each lobe, so it has four pollen-sacs. A sterile stamen is a staminode.
Mono, Di, Poly = 1, 2, many bundles: china rose, pea, citrus. Say "Rose, Pea, Citrus" as the number of bundles rises. Epipetalous = on petals (brinjal); epiphyllous = on the perianth (lily).
8. Gynoecium and Placentation
8.1 Gynoecium
- The gynoecium is the female reproductive part of the flower.
- It is made up of one or more carpels.
- ★ Exam imp A carpel has three parts: stigma, style and ovary.
- Ovary: the enlarged basal part.
- Style: the elongated tube on the ovary; it connects the ovary to the stigma.
- Stigma: usually at the tip of the style; the receptive surface for pollen grains.
- Each ovary bears one or more ovules attached to a flattened, cushion-like placenta.
- Apocarpous: carpels free, as in lotus and rose.
- Syncarpous: carpels fused, as in mustard and tomato.
- After fertilisation, the ovules develop into seeds and the ovary matures into a fruit.
- More than one carpel, free
- Lotus, rose
- More than one carpel, fused
- Mustard, tomato
8.2 Placentation
- ★ Exam imp Placentation: the arrangement of ovules within the ovary.
- Five types are described: marginal, axile, parietal, free central and basal.
| Type | Arrangement of ovules | Examples |
|---|---|---|
| Marginal | Placenta forms a ridge along the ventral suture of the ovary; ovules on this ridge form two rows | Pea |
| Axile | Placenta is axial; ovules attached to it in a multilocular ovary | China rose, tomato, lemon |
| Parietal | Ovules on the inner wall (peripheral part) of the ovary; the one-chambered ovary becomes two-chambered by a false septum | Mustard, Argemone |
| Free central | Ovules on a central axis; septa absent | Dianthus, primrose |
| Basal | Placenta at the base of the ovary; a single ovule attached to it | Sunflower, marigold |
Placentation examples: Pea on the Margin; T-L-C on the Axis (Tomato, Lemon, China rose); M-A on the wall (Mustard, Argemone, parietal); D-P in the free centre (Dianthus, Primrose); S-M at the base (Sunflower, Marigold).
- Septa: present in axile (multilocular ovary); absent in free central; a false septum in parietal.
- Single ovule only in basal placentation.
- China rose appears in four lists: hypogynous, twisted aestivation, monoadelphous stamens and axile placentation. Mustard appears in hypogynous, actinomorphic, syncarpous and parietal.
9. Exam Essentials
Pairs to Match
| List I | List II |
|---|---|
| Racemose inflorescence | Acropetal succession |
| Cymose inflorescence | Basipetal order |
| Perianth | Lily |
| Asymmetric flower | Canna |
| Bract | Reduced leaf at the base of the pedicel |
| Hypogynous flower | Superior ovary |
| Perigynous flower | Half inferior ovary |
| Epigynous flower | Inferior ovary |
| Valvate aestivation | Calotropis |
| Vexillary aestivation | Pea, bean |
| Staminode | Sterile stamen |
| Epiphyllous stamens | Lily |
| Polyadelphous stamens | Citrus |
| Stigma | Receptive surface for pollen grains |
| Free central placentation | Dianthus |
Numbers to Remember
- 4 floral whorls: 2 accessory and 2 reproductive.
- Trimerous, tetramerous, pentamerous: parts in multiples of 3, 4, 5.
- Vexillary corolla: 5 petals = 1 standard + 2 wings + 2 keel petals.
- Anther: usually 2 lobes, each with 2 pollen-sacs.
- Carpel: 3 parts. Marginal placentation: ovules in 2 rows. Basal: 1 ovule.
- Diadelphous: 2 bundles; polyadelphous: more than 2 bundles.
Examples to Remember
| Feature | Examples |
|---|---|
| Actinomorphic | Mustard, datura, chilli |
| Zygomorphic | Pea, gulmohur, bean, Cassia |
| Hypogynous (superior ovary) | Mustard, china rose, brinjal |
| Perigynous (half inferior) | Plum, rose, peach |
| Epigynous (inferior) | Guava, cucumber, ray florets of sunflower |
| Twisted aestivation | China rose, lady's finger, cotton |
| Imbricate aestivation | Cassia, gulmohur |
| Epipetalous stamens | Brinjal |
| Monoadelphous / diadelphous | China rose / pea |
| Unequal filaments | Salvia, mustard |
| Apocarpous / syncarpous | Lotus, rose / mustard, tomato |
| Axile placentation | China rose, tomato, lemon |
| Parietal placentation | Mustard, Argemone |
| Basal placentation | Sunflower, marigold |
- A flower formed from a shoot tip is always solitary.
- In lily, the calyx and corolla are not distinct: they form a perianth.
- Canna is asymmetric: no vertical plane divides it into similar halves.
- Valvate margins only touch; they do not overlap.
- Imbricate margins overlap but not in any particular direction.
- Free central placentation has no septa; basal placentation has only one ovule.
- In epigynous flowers, the ray florets of sunflower have an inferior ovary.
What is aestivation?
Name the placentation in which the ovary becomes two-chambered due to a false septum.
What is the position of the ovary in rose?
Name the stamen condition of pea.
In a vexillary figure, name the innermost two petals.
10. Quick Revision
- Flower: modified shoot; floral meristem; condensed axis; floral appendages instead of leaves.
- Inflorescence: arrangement of flowers on the floral axis.
- Racemose: axis grows, acropetal. Cymose: axis ends in a flower, basipetal.
- Four whorls on the thalamus; calyx and corolla accessory, androecium and gynoecium reproductive.
- Perianth in lily. Bisexual: both sexes; unisexual: one only.
- Actinomorphic: mustard, datura, chilli; zygomorphic: pea, gulmohur, bean, Cassia; asymmetric: canna.
- Tri-, tetra-, pentamerous: multiples of 3, 4, 5. Bract: reduced leaf at the pedicel base.
- Hypogynous: superior; perigynous: half inferior; epigynous: inferior.
- Calyx: sepals, protect the bud; gamosepalous or polysepalous.
- Corolla: petals, attract insects; tubular, bell-, funnel- or wheel-shaped.
- Aestivation: valvate, twisted, imbricate, vexillary (standard, wings, keel).
- Stamen: filament and bilobed anther; staminode is sterile.
- Epipetalous (brinjal), epiphyllous (lily); mono- (china rose), di- (pea), polyadelphous (citrus).
- Carpel: stigma, style, ovary; apocarpous (lotus, rose) or syncarpous (mustard, tomato).
- Placentation: marginal, axile, parietal, free central, basal.
11. Solved Examples
List I: A. Valvate; B. Twisted; C. Imbricate; D. Vexillary
List II: I. Gulmohur; II. Bean; III. Calotropis; IV. Lady's finger
Choose the correct answer.
(A) A-III, B-I, C-IV, D-II
(B) A-IV, B-III, C-I, D-II
(C) A-III, B-IV, C-I, D-II
(D) A-II, B-IV, C-I, D-III
Answer: (C). Calotropis is valvate, lady's finger twisted, gulmohur imbricate and bean vexillary.
List I: A. Marginal; B. Axile; C. Free central; D. Basal
List II: I. Marigold; II. Lemon; III. Pea; IV. Dianthus
Choose the correct answer.
(A) A-III, B-II, C-IV, D-I
(B) A-II, B-III, C-IV, D-I
(C) A-III, B-IV, C-II, D-I
(D) A-I, B-II, C-IV, D-III
Answer: (A). Pea is marginal, lemon axile, Dianthus free central and marigold basal.
A. In racemose inflorescence, flowers are borne in basipetal order.
B. Plum, rose and peach have a half inferior ovary.
C. A sterile stamen is called a staminode.
D. Stamens of pea are monoadelphous.
E. In epigynous flowers, the thalamus fuses with the ovary.
Choose the correct answer.
(A) A, B and C only
(B) B, C and E only
(C) C, D and E only
(D) A, D and E only
Answer: (B). A is false: racemose flowers are acropetal. D is false: pea stamens are diadelphous. B, C and E are true.
A. Keel; B. Standard; C. Wings
Choose the correct order.
(A) A, C, B
(B) C, B, A
(C) B, A, C
(D) B, C, A
Answer: (D). The standard overlaps the two wings, which overlap the two keel petals.
(A) Mustard
(B) China rose
(C) Brinjal
(D) Cucumber
Answer: (D). Cucumber is epigynous with an inferior ovary. Mustard, china rose and brinjal are hypogynous.
Statement II: In free central placentation, the ovary is divided by septa.
Choose the correct answer.
(A) Both Statement I and Statement II are correct
(B) Both Statement I and Statement II are incorrect
(C) Statement I is correct but Statement II is incorrect
(D) Statement I is incorrect but Statement II is correct
Answer: (C). In free central placentation, the ovules lie on a central axis and septa are absent.
12. Practice Questions
- What is a flower? Describe the parts of a typical angiosperm flower.Answer: A flower is a modified shoot meant for sexual reproduction. On the thalamus at the end of the pedicel it bears the calyx (sepals), corolla (petals), androecium (stamens: filament and anther) and gynoecium (carpels: stigma, style, ovary).
- Define the term inflorescence. Explain the basis for the different types of inflorescence in flowering plants.Answer: Inflorescence is the arrangement of flowers on the floral axis. The basis is whether the apex keeps growing (racemose, acropetal flowers) or ends in a flower (cymose, limited growth, basipetal flowers).
- Define: (a) aestivation (b) placentation (c) actinomorphic (d) zygomorphic (e) superior ovary (f) perigynous flower (g) epipetalous stamen.Answer: (a) Arrangement of sepals or petals in the bud. (b) Arrangement of ovules in the ovary. (c) Divisible into equal radial halves in any radial plane. (d) Divisible into similar halves in one vertical plane only. (e) Ovary above the other parts (hypogynous). (f) Other parts on the rim of the thalamus around a half inferior ovary. (g) Stamen attached to a petal.
- Differentiate between (a) racemose and cymose inflorescence (b) apocarpous and syncarpous ovary.Answer: (a) Racemose: axis grows, acropetal; cymose: axis ends in a flower, basipetal. (b) Apocarpous: carpels free (lotus, rose); syncarpous: carpels fused (mustard, tomato).
- Describe the arrangement of floral members in relation to their insertion on the thalamus.Answer: Hypogynous: gynoecium highest, superior ovary (mustard). Perigynous: other parts on the rim at about the ovary level, half inferior ovary (rose). Epigynous: thalamus encloses and fuses with the ovary, other parts above it, inferior ovary (guava).
- Describe the various types of placentation found in flowering plants.Answer: Marginal: ridge along the ventral suture, two rows (pea). Axile: axial placenta in a multilocular ovary (china rose, tomato, lemon). Parietal: on the inner wall, false septum (mustard, Argemone). Free central: central axis, no septa (Dianthus, primrose). Basal: one ovule at the base (sunflower, marigold).
- Match List I with List II. List I: A. Epiphyllous; B. Monoadelphous; C. Polyadelphous; D. Epipetalous. List II: I. Citrus; II. Brinjal; III. Lily; IV. China rose.
(1) A-III, B-IV, C-I, D-II
(2) A-IV, B-III, C-I, D-II
(3) A-III, B-I, C-IV, D-II
(4) A-II, B-IV, C-I, D-IIIAnswer: (1). Lily: epiphyllous; china rose: monoadelphous; citrus: polyadelphous; brinjal: epipetalous. - Read the statements. A. Calyx and corolla are reproductive organs. B. The stigma is the receptive surface for pollen. C. Lotus and rose are apocarpous. D. Canna is asymmetric.
(1) B, C and D only
(2) A, B and C only
(3) A and D only
(4) A, C and D onlyAnswer: (1). A is false: calyx and corolla are accessory organs. - Which is NOT an example of zygomorphic flowers?
(a) Pea
(b) Gulmohur
(c) Cassia
(d) ChilliAnswer: (d) Chilli, which is actinomorphic.
Common Mistakes to Avoid
- Linking racemose with basipetal order. Correct: racemose is acropetal; cymose is basipetal.
- Calling calyx and corolla reproductive whorls. They are accessory organs.
- Giving rose as hypogynous. Rose is perigynous with a half inferior ovary.
- Writing that the ovary is superior in epigynous flowers. It is inferior.
- Mixing twisted and imbricate: twisted overlaps in one direction; imbricate in no particular direction.
- Calling pea stamens monoadelphous. Pea is diadelphous; china rose is monoadelphous.
- Placing septa in free central placentation. Septa are absent there.
- Writing that the ovule becomes the fruit. The ovary becomes the fruit; the ovule becomes the seed.
Frequently Asked Questions
What is the difference between racemose and cymose inflorescence?
In racemose inflorescence, the main axis continues to grow and flowers are borne laterally in acropetal succession, with the oldest at the base. In cymose inflorescence, the main axis ends in a flower, so growth is limited and flowers are borne in basipetal order.
Why is a flower called a modified shoot?
In a flower, the shoot apical meristem changes into a floral meristem. The internodes do not elongate, so the axis is condensed, and the apex produces floral appendages at successive nodes instead of leaves. A shoot tip that becomes a flower is always solitary.
What are hypogynous, perigynous and epigynous flowers?
They describe the position of the calyx, corolla and androecium relative to the ovary. Hypogynous flowers have a superior ovary (mustard), perigynous flowers a half inferior ovary (rose, plum, peach), and epigynous flowers an inferior ovary (guava, cucumber).
What is vexillary aestivation?
Vexillary, or papilionaceous, aestivation is seen in pea and bean. Of the five petals, the largest, the standard, overlaps the two lateral wings, which in turn overlap the two smallest anterior petals, the keel.
What is the difference between valvate, twisted and imbricate aestivation?
In valvate aestivation, the margins just touch without overlapping (Calotropis). In twisted, each margin overlaps the next one in one direction (china rose, lady's finger, cotton). In imbricate, margins overlap in no particular direction (Cassia, gulmohur).
What are monoadelphous, diadelphous and polyadelphous stamens?
These terms describe stamens united by their filaments. Monoadelphous stamens form one bundle (china rose), diadelphous stamens two bundles (pea) and polyadelphous stamens more than two bundles (citrus). Free stamens are called polyandrous.
What are the types of placentation with examples?
Marginal (pea), axile (china rose, tomato, lemon), parietal (mustard, Argemone), free central (Dianthus, primrose) and basal (sunflower, marigold). The type depends on where the placenta lies and how the ovules are attached within the ovary.
How important is the flower topic of NCERT morphology for NEET?
Very important. Morphology of flowering plants is among the most frequently tested Class 11 chapters in NEET. Many of its questions test the flower: aestivation, ovary position, stamen conditions and placentation. They usually come as match-the-list and statement questions.
Previous year questions on The Flower
15 questions from past papers, each with a step-by-step solution.
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