Q.Write the floral formula of Datura metel.

Floral Formula and Floral Diagram: A First Look

Imagine you are a botanist who has just collected a flower from the field. You need to record its structure — but you cannot carry a pressed flower everywhere, and a photograph does not show the internal arrangement of stamens and carpels. You need a shorthand, a code that captures everything about the flower in a single line or a simple sketch. That is exactly what a floral formula and a floral diagram do.

A floral formula is a symbolic code using letters, numbers, and signs. A floral diagram is a schematic cross-section of the flower bud, showing the relative positions of the whorls. Together they let you describe any flower precisely, without ambiguity.

The Intuition: What Must a Flower Description Capture?

A flower has four whorls, arranged from outside to inside:

1. Calyx — the sepals (usually green, protective)
2. Corolla — the petals (often coloured, attractive)
3. Androecium — the stamens (male reproductive parts)
4. Gynoecium — the carpels (female reproductive parts)

But that is not enough. You also need to know:

• Symmetry — Is the flower radially symmetric (actinomorphic) like a buttercup, or bilaterally symmetric (zygomorphic) like a pea flower, or asymmetric?
• Cohesion — Are the sepals free (polysepalous) or fused (gamosepalous)? Are the petals free (polypetalous) or fused (gamopetalous)? Are the stamens free or fused to each other or to the petals?
• Adhesion — Are the stamens attached to the petals (epipetalous)? Is the ovary superior or inferior?
• Number — How many sepals, petals, stamens, and carpels are there?
• Sex — Is the flower bisexual (bisexual) or unisexual (male or female)?

The floral formula encodes all of this. The floral diagram shows it visually.

The Floral Formula: The Code

A floral formula is written as a single line, usually starting with a symbol for symmetry, then the four whorls in order, and ending with the sex symbol. Here is the standard structure:

1. Symmetry

2. Calyx (K)

The letter K (from German Kelch) is used. Write the number of sepals after it. If the sepals are fused, put the number in brackets. If they are free, no brackets.

• $K_5$ — 5 free sepals
• $K_{(5)}$ — 5 fused sepals

3. Corolla (C)

The letter C (from Latin Corolla) is used. Same rule: number in brackets if fused, no brackets if free.

• $C_5$ — 5 free petals
• $C_{(5)}$ — 5 fused petals

4. Androecium (A)

The letter A (from Androecium). Write the number of stamens. If stamens are fused to the corolla (epipetalous), write the number after a line: $A_{5 \mid C}$ means 5 stamens attached to petals. If stamens are fused to each other, use brackets: $A_{(5)}$ means 5 stamens fused into a single bundle (monadelphous). Two bundles: $A_{(5)+(5)}$ (diadelphous). Many bundles: $A_{(\infty)}$ (polyadelphous).

5. Gynoecium (G)

The letter G (from Gynoecium). Write the number of carpels, then a line, then the number of locules (chambers) in the ovary. The position of the ovary is shown by a line above or below the number:

• $G_3$ — superior ovary, 3 carpels
• $\overline{G}_3$ — inferior ovary, 3 carpels
• $G_{\underline{3}}$ — half-inferior ovary (rare in Indian syllabus)

Often you will see $G_{(3)}$ if the carpels are fused (syncarpous) or $G_3$ if free (apocarpous). The number of locules is written after a colon: $G_{(3):3}$ means 3 fused carpels, 3 locules.

6. Sex

• $\overset{\wedge}{\underset{\wedge}{}}$ or $\bigcirc$ — bisexual flower
• $\male$ — male (staminate) flower
• $\female$ — female (pistillate) flower

Putting It All Together

A typical formula for a bisexual, actinomorphic flower with 5 free sepals, 5 free petals, many free stamens, and a superior ovary of 5 fused carpels:

For a pea flower (zygomorphic, 5 fused sepals, 5 petals (one standard, two wings, two keel), 10 stamens (9 fused + 1 free), 1 carpel, superior ovary):

The Floral Diagram: The Picture

A floral diagram is a top view of the flower bud, drawn as if you sliced the bud horizontally just above the ovary and looked down. It shows the exact arrangement of the whorls.

Conventions

• The axis (stem) is drawn as a small circle or dot at the top of the diagram.
• The bract (a leaf-like structure below the flower) is drawn as a curved line opposite the axis.
• The calyx is drawn as the outermost whorl of sepals, usually green.
• The corolla is the next whorl, usually coloured (or drawn as outlines).
• The androecium is inside the corolla, drawn as stamens with anthers.
• The gynoecium is at the centre, drawn as a cross-section of the ovary showing the locules and ovules.

Key Rules for Drawing

1. Position relative to the axis: The posterior sepal (the one nearest the axis) is drawn at the top. The anterior sepal (opposite the axis) is at the bottom. This matters for zygomorphic flowers.

2. Cohesion: If sepals are fused, they are drawn touching each other. If free, they are drawn with gaps. Same for petals.

3. Adhesion: If stamens are epipetalous, they are drawn attached to the petals.

4. Placentation: The arrangement of ovules inside the ovary is shown in the centre. For example, marginal placentation (pea) shows ovules along the fused edge; axile placentation (tomato) shows ovules in the centre.

5. Symmetry: An actinomorphic flower has a diagram that looks the same from all sides. A zygomorphic flower has a clear left-right symmetry, with the axis at the top.

A Worked Example: Hibiscus (China Rose)

Let us apply this to a familiar flower.

Observation: Hibiscus has 5 sepals (fused at base), 5 petals (free, but twisted in bud), many stamens (fused into a tube around the style), 5 carpels (fused, superior ovary, 5 locules), actinomorphic, bisexual.

Floral formula:

Floral diagram (describe it):

• Axis at top.
• Bract below (epicalyx present in hibiscus, drawn as a whorl of small structures outside the calyx).
• Calyx: 5 fused sepals drawn as a continuous ring.
• Corolla: 5 free petals drawn as separate arcs inside the calyx.
• Androecium: Many stamens drawn as a ring of small circles (anthers) on a fused tube.
• Gynoecium: Central circle with 5 lines radiating from the centre (5 locules), each with ovules.

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