Morphology of Flowering Plants

Given: Two types of compound leaves — pinnately compound and palmately compound.

Concept: In a compound leaf, the lamina (leaf blade) is divided into several leaflets. The manner in which leaflets are arranged distinguishes the two types.

| Feature | Pinnately Compound Leaf | Palmately Compound Leaf |
|---|---|---|
| Definition | The leaflets (pinnae) are arranged on both sides of a common axis called the rachis (an extension of the petiole). | The leaflets are attached at a single point — the tip of the petiole — and spread out like fingers of a hand. |
| Rachis | Present (midrib-like axis). | Absent; leaflets arise from one point. |
| Arrangement of leaflets | Along the rachis on either side. | Radiate from the tip of the petiole. |
| Examples | Neem (*Azadirachta indica*), Rose, Cassia. | Silk cotton (*Bombax*), Hemp (*Cannabis*), Cleome. |

Conclusion: The key difference is the presence of a rachis in pinnately compound leaves, whereas in palmately compound leaves all leaflets arise from a common point at the tip of the petiole.

Definition: Phyllotaxy is the pattern or arrangement of leaves on the stem or branch. It is of three main types:

1. Alternate Phyllotaxy:
- A single leaf arises at each node alternately.
- The leaves are arranged in a spiral manner along the stem.
- Examples: China rose (*Hibiscus rosa-sinensis*), Mustard (*Brassica*), Sunflower.

2. Opposite Phyllotaxy:
- Two leaves arise at each node, opposite to each other.
- It is of two sub-types:
- Opposite superposed: Pairs of leaves at successive nodes are in the same plane. *Example:* Calotropis.
- Opposite decussate: Pairs of leaves at successive nodes are at right angles (90°) to each other. *Example:* Guava (*Psidium*).

3. Whorled Phyllotaxy:
- More than two leaves arise at each node and form a whorl (ring) around the stem.
- Examples: Nerium (*Nerium oleander*), Alstonia.

Significance: Phyllotaxy ensures maximum exposure of leaves to sunlight and minimises overlapping, thus optimising photosynthesis.

(a) Aestivation:
The mode of arrangement of sepals or petals in a floral bud with respect to the other members of the same whorl is called aestivation. Main types are:
- Valvate: Margins of sepals/petals just touch each other without overlapping. *Example:* Calotropis.
- Twisted (Contorted): One margin of each petal overlaps the next petal. *Example:* China rose.
- Imbricate: Margins overlap irregularly. *Example:* Cassia.
- Vexillary: Largest petal (standard) overlaps two lateral petals (wings), which in turn overlap two smallest petals (keel). *Example:* Pea.

(b) Placentation:
The arrangement of ovules within the ovary on the placenta is called placentation. Types include axile, marginal, parietal, basal, free central, and superficial.

(c) Actinomorphic:
When a flower can be divided into two equal radial halves in any vertical plane passing through the centre, it is called actinomorphic (radially symmetrical).
*Example:* Mustard, Datura, Chilli.

(d) Zygomorphic:
When a flower can be divided into two equal halves in only one particular vertical plane, it is called zygomorphic (bilaterally symmetrical).
*Example:* Pea, Gulmohar, Bean, Cassia.

(e) Superior Ovary:
When the ovary is situated above the level of insertion of other floral parts (sepals, petals, stamens) on the thalamus, the ovary is called superior and the flower is called hypogynous.
*Example:* Mustard, Brinjal, China rose.

(f) Perigynous Flower:
When the gynoecium is situated in the centre and other floral parts are borne on the rim of the thalamus (which is more or less at the same level as the ovary), the flower is called perigynous. The ovary here is called half inferior.
*Example:* Plum, Rose, Peach.

(g) Epipetalous Stamen:
When the stamens are attached to the petals (adnate to petals), they are called epipetalous stamens.
*Example:* Brinjal, Datura (family Solanaceae).

(a) Racemose vs. Cymose Inflorescence:

| Feature | Racemose Inflorescence | Cymose Inflorescence |
|---|---|---|
| Growth of main axis | Main axis continues to grow indefinitely (monopodial). | Main axis terminates in a flower; growth is limited (sympodial). |
| Order of flower opening | Flowers open from base to apex (acropetal succession). | Flowers open from apex to base (basipetal succession). |
| Position of oldest flower | At the base of the inflorescence. | At the apex (top) of the inflorescence. |
| Examples | Mustard, Radish, Amaranthus. | Jasmine (*Jasminum*), Solanum, Bougainvillea. |

(b) Apocarpous vs. Syncarpous Ovary:

| Feature | Apocarpous Ovary | Syncarpous Ovary |
|---|---|---|
| Definition | The gynoecium has free (unfused) carpels. | The gynoecium has fused carpels. |
| Number of carpels | More than one, all free. | More than one, all united together. |
| Examples | Rose, Lotus, Ranunculus. | Mustard, Tomato, China rose. |

(i) Gram Seed (Dicotyledonous seed):

Gram (*Cicer arietinum*) is a non-endospermic (ex-albuminous) dicot seed.

Labelled diagram description (draw and label the following parts):

$$\text{Gram Seed (Dicot — Non-endospermic)}$$

Key parts to label:
1. Seed coat (Testa) — outer hard covering.
2. Tegmen — inner thin layer of seed coat.
3. Hilum — scar on seed coat where seed was attached to funicle.
4. Micropyle — small pore near hilum.
5. Embryo axis (Embryonal axis):
- Plumule — embryonic shoot (upper end).
- Radicle — embryonic root (lower end).
6. Cotyledons (2) — two large, fleshy food-storing cotyledons attached to embryo axis.

*(Note: Endosperm is absent in mature gram seed as it is consumed by the developing embryo.)*

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(ii) V.S. of Maize Seed (Monocotyledonous seed):

Maize (*Zea mays*) is an endospermic (albuminous) monocot seed.

Labelled diagram description (draw and label the following parts):

$$\text{V.S. of Maize Seed (Monocot — Endospermic)}$$

Key parts to label:
1. Pericarp — fused with seed coat (fruit wall and seed coat are indistinguishable).
2. Endosperm — large, bulky, stores food (starch); divided into:
- Aleurone layer — outermost proteinaceous layer of endosperm.
3. Embryo (small, situated at one end):
- Scutellum (Cotyledon) — single cotyledon; shield-shaped; absorbs food from endosperm.
- Plumule — enclosed in coleoptile (protective sheath).
- Radicle — enclosed in coleorhiza (protective sheath).
- Embryonal axis connecting plumule and radicle.

*(Students must draw neat, labelled diagrams in the answer sheet for full marks.)*

Flower chosen: Datura (*Datura stramonium*) or Tomato (*Solanum lycopersicum*) — Family Solanaceae.

Semi-technical Description of Datura:

Vegetative Characters:
- Habit: Erect, branched herb.
- Root: Tap root system.
- Stem: Erect, cylindrical, branched, solid, green, hairy.
- Leaves: Simple, exstipulate, alternate, petiolate, ovate, unicostate reticulate venation, hairy.

Floral Characters:
- Inflorescence: Solitary, axillary cymose.
- Flower: Bisexual, actinomorphic, complete, hypogynous, bracteate.
- Calyx: Sepals 5, gamosepalous (united), persistent, green, valvate aestivation.
- Corolla: Petals 5, gamopetalous (united), funnel-shaped, white or violet, valvate aestivation.
- Androecium: Stamens 5, epipetalous (attached to petals), alternating with petals, anthers dithecous, basifixed.
- Gynoecium: Bicarpellary, syncarpous; ovary superior, bilocular (with false septum making it appear 4-locular), axile placentation with many ovules; style long, simple; stigma bilobed.
- Fruit: Spinous capsule.
- Seeds: Many, endospermous.

Floral Formula:
$$\oplus\, \bigcirc\, K_{(5)}\, C_{(5)}\, A_5\, G_{(2)}$$

Where:
- $\oplus$ = actinomorphic
- $\bigcirc$ = bisexual
- $K_{(5)}$ = 5 united sepals
- $C_{(5)}$ = 5 united petals
- $A_5$ = 5 stamens (epipetalous)
- $G_{(2)}$ = bicarpellary, syncarpous, superior ovary

Floral Diagram:
*(Draw a floral diagram showing the following from outside to inside:)*
1. Outermost whorl: 5 sepals (valvate, united at base) — draw as 5 segments touching at margins.
2. Next whorl: 5 petals (valvate, united) — alternating with sepals.
3. Next whorl: 5 stamens — each attached to a petal (epipetalous).
4. Centre: Bicarpellary ovary — draw as a circle divided into 2 locules with ovules on axile placenta; obliquely placed.

*(Note: In the floral diagram, the mother axis is shown at the top and the bract at the bottom.)*

Definition: The arrangement of ovules within the ovary on the placenta is called placentation.

The following types of placentation are found in flowering plants:

1. Marginal Placentation:
- The placenta forms a ridge along the ventral suture of the ovary.
- Ovules are borne in two rows on this ridge.
- Ovary is unilocular.
- *Example:* Pea (*Pisum sativum*), Bean.

2. Axile Placentation:
- The margins of carpels fuse to form a central axis (septum) in a multilocular ovary.
- Ovules are attached to the central axis.
- *Example:* China rose (*Hibiscus*), Tomato, Lemon.

3. Parietal Placentation:
- Ovules develop on the inner wall of the ovary or on peripheral (parietal) areas.
- Ovary is unilocular but may become bilocular due to formation of a false septum.
- *Example:* Mustard (*Brassica*), Argemone.

4. Free Central Placentation:
- Ovules are borne on a central column (axis) that arises from the base of the ovary.
- The central axis is not connected to the ovary wall by septa.
- Ovary is unilocular.
- *Example:* Dianthus, Primrose.

5. Basal Placentation:
- The placenta develops at the base of the ovary.
- A single ovule is attached to the base.
- Ovary is unilocular.
- *Example:* Sunflower (*Helianthus*), Marigold.

6. Superficial Placentation:
- Ovules are borne all over the inner surface of the locule walls.
- Ovary is multilocular.
- *Example:* Water lily (*Nymphaea*).

Summary Table:

| Type | Position of ovules | Locules | Example |
|---|---|---|---|
| Marginal | Ventral suture | 1 | Pea |
| Axile | Central axis | Many | Hibiscus |
| Parietal | Inner wall | 1 (or 2) | Mustard |
| Free central | Central column | 1 | Dianthus |
| Basal | Base of ovary | 1 | Sunflower |
| Superficial | Inner surface of locule | Many | Nymphaea |

What is a Flower?
A flower is a modified shoot meant for sexual reproduction. It is a condensed shoot in which the internodes are suppressed and the leaves are modified into floral organs. The thalamus (receptacle) bears all the floral parts.

Parts of a Typical Angiosperm Flower:

A typical (complete) flower consists of four whorls attached to the thalamus:

1. Calyx (Outermost whorl):
- Made up of sepals (individual units).
- Usually green and leaf-like; protect the flower in bud stage.
- May be gamosepalous (united) or polysepalous (free).
- May be persistent (remain after fertilisation, e.g., brinjal) or caducous (fall off early).

2. Corolla (Second whorl):
- Made up of petals (individual units).
- Usually brightly coloured to attract pollinators.
- May be gamopetalous (united) or polypetalous (free).
- Show various types of aestivation (valvate, twisted, imbricate, vexillary).

3. Androecium (Third whorl — Male reproductive organ):
- Made up of stamens.
- Each stamen has:
- Filament — stalk of the stamen.
- Anther — bilobed structure at the tip; produces pollen grains (male gametes).
- Stamens may be free (polyandrous) or united in various ways.
- May be attached to petals (epipetalous) or to perianth (epiphyllous).

4. Gynoecium (Innermost whorl — Female reproductive organ):
- Made up of carpels (pistils).
- Each carpel has three parts:
- Ovary — basal swollen part; contains ovules (which develop into seeds after fertilisation).
- Style — elongated stalk connecting ovary to stigma.
- Stigma — apical part; receives pollen grains.
- Carpels may be free (apocarpous) or fused (syncarpous).
- Ovary position may be superior (hypogynous), half inferior (perigynous), or inferior (epigynous).

Additional Parts (may or may not be present):
- Bract: Modified leaf at the base of the flower.
- Bracteoles: Small bracts on the pedicel.
- Pedicel: Stalk of the flower.
- Nectaries: Secrete nectar to attract pollinators.

Conclusion: A typical angiosperm flower is thus a highly specialised structure adapted for sexual reproduction, with each whorl performing a specific function.

Definition of Inflorescence:
The arrangement of flowers on the floral axis (peduncle) is called inflorescence. When a shoot tip transforms into a flower-bearing axis, the pattern in which flowers are arranged on it constitutes the inflorescence.

Basis for Classification:
The main basis for distinguishing types of inflorescence is:
1. Whether the main axis (peduncle) continues to grow or terminates in a flower.
2. The order of opening of flowers (acropetal or basipetal).

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Types of Inflorescence:

A. Racemose (Indefinite / Indeterminate) Inflorescence:
- The main axis continues to grow indefinitely and does not terminate in a flower.
- Flowers are borne laterally in acropetal succession (older flowers at base, younger at apex).
- Sub-types:
1. Raceme: Flowers pedicellate (stalked) on an unbranched axis. *Example:* Mustard, Radish.
2. Spike: Flowers sessile (unstalked) on an unbranched axis. *Example:* Achyranthes.
3. Catkin (Ament): Spike with unisexual flowers on a pendulous axis. *Example:* Mulberry, Oak.
4. Spadix: Spike with fleshy axis enclosed in a large bract (spathe). *Example:* Banana, Colocasia.
5. Corymb: Flowers at different levels but reaching the same height (flat-topped). *Example:* Candytuft (*Iberis*).
6. Umbel: All pedicels arise from the same point; flat-topped. *Example:* Coriander, Fennel.
7. Capitulum (Head): Sessile flowers on a flattened/convex receptacle; oldest flowers at periphery. *Example:* Sunflower, Marigold.
8. Panicle: Branched raceme. *Example:* Neem, Mango.

B. Cymose (Definite / Determinate) Inflorescence:
- The main axis terminates in a flower (growth is limited).
- Flowers open in basipetal succession (oldest flower at apex, younger below).
- Sub-types:
1. Monochasial (Uniparous) Cyme: Each axis produces one lateral branch ending in a flower.
- *Helicoid cyme:* Branches develop on the same side. *Example:* Heliotropium.
- *Scorpioid cyme:* Branches develop alternately on opposite sides. *Example:* Freesia.
2. Dichasial (Biparous) Cyme: Each axis produces two lateral branches. *Example:* Jasmine, Teak.
3. Polychasial (Multiparous) Cyme: Each axis produces more than two lateral branches. *Example:* Calotropis.

Special Types:
- Hypanthodium: Fleshy hollow receptacle with flowers inside. *Example:* Ficus (banyan, peepal).
- Cyathium: Cup-shaped involucre with one female and many male flowers. *Example:* Euphorbia.

Conclusion: The type of inflorescence is determined primarily by the growth pattern of the main axis and the sequence of flower opening.

Introduction:
The position of the ovary relative to other floral parts (calyx, corolla, androecium) on the thalamus (receptacle) determines the nature of the flower. Based on this, flowers are classified into three types:

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1. Hypogynous Flower (Superior Ovary):
- The thalamus is convex or conical.
- The gynoecium (ovary) is situated at the highest point on the thalamus.
- Sepals, petals, and stamens are inserted below the ovary (hence the name — hypo = below, gynous = ovary).
- The ovary is called superior.
- *Examples:* Mustard (*Brassica*), Brinjal (*Solanum melongena*), China rose (*Hibiscus*).

$$\text{Thalamus (convex)} \rightarrow \text{Sepals, Petals, Stamens below} \rightarrow \text{Ovary at top (Superior)}$$

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2. Perigynous Flower (Half-inferior Ovary):
- The thalamus grows upward around the ovary forming a cup-shaped or flat structure (hypanthium).
- The gynoecium is situated in the centre of the cup.
- Sepals, petals, and stamens are borne on the rim of the thalamus at the same level as the ovary.
- The ovary is called half inferior (semi-inferior).
- *Examples:* Rose (*Rosa*), Plum (*Prunus*), Peach.

$$\text{Thalamus (cup-shaped)} \rightarrow \text{Sepals, Petals, Stamens on rim} \rightarrow \text{Ovary in centre (Half inferior)}$$

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3. Epigynous Flower (Inferior Ovary):
- The thalamus grows completely over and around the ovary, enclosing it.
- The margins of the thalamus fuse with the ovary wall.
- Sepals, petals, and stamens appear to arise above the ovary (hence epi = above, gynous = ovary).
- The ovary is called inferior.
- *Examples:* Guava (*Psidium*), Cucumber (*Cucumis*), Sunflower (*Helianthus*), Ray florets of sunflower.

$$\text{Thalamus (fused with ovary)} \rightarrow \text{Sepals, Petals, Stamens above} \rightarrow \text{Ovary at bottom (Inferior)}$$

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Summary Table:

| Type of Flower | Position of Ovary | Thalamus Shape | Example |
|---|---|---|---|
| Hypogynous | Superior | Convex/conical | Mustard, Hibiscus |
| Perigynous | Half inferior | Cup-shaped | Rose, Plum |
| Epigynous | Inferior | Fused over ovary | Guava, Sunflower |

Conclusion: The arrangement of floral members on the thalamus is an important taxonomic character used in the classification and identification of flowering plants.