Morphology of Flowering Plants

MORPHOLOGY OF FLOWERING PLANTS

**Definition:** Morphology refers to the study of the external form and structure of plants. It involves observing and describing the gross structural features of living organisms, both external and internal, using naked eyes, magnifying lenses, or microscopes. This foundational knowledge forms the basis for classification, identification, and understanding physiological processes in plants.

**Historical Importance:** Before experimental biology emerged, naturalists described organisms solely through morphological observations—this was called natural history. Today, these detailed structural descriptions are essential for asking research questions in physiology and evolutionary biology. Understanding plant morphology enables proper classification and systematic identification of flowering plants.

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THE ROOT

**Definition:** The root is the underground vegetative part of a plant that develops from the radicle of the embryo. It grows vertically downward into the soil and forms the foundation of the plant.

**Main Functions of Root System:**

**Absorption:** Water and mineral nutrients from soil

**Anchorage:** Provides structural support and holds the plant firmly in soil

**Storage:** Reserves food materials (e.g., carrot, turnip, beet store starch)

**Synthesis:** Production of plant growth regulators (hormones like auxins and cytokinins)

**Conduction:** Transport of absorbed materials to other plant parts

Types of Root Systems

**1. Tap Root System**

Found in dicotyledonous plants (e.g., mustard, gram, pea)

Primary root elongates directly from radicle and grows deep into soil

Lateral roots branch from primary root in orders: secondary, tertiary, etc.

Primary root and all its branches = tap root system

**Advantage:** Can reach deeper soil layers for water during drought

**2. Fibrous Root System**

Found in monocotyledonous plants (e.g., wheat, rice, maize, grass)

Primary root is short-lived and degenerates early

Replaced by numerous roots arising from base of stem

All roots are similar in size and branching

Form a net-like, spreading mass in upper soil

**Advantage:** Better for soil coverage and water absorption from shallow layers

**3. Adventitious Root System**

Roots arising from parts of plant other than radicle (non-radical origin)

Found in grass, Monstera (Swiss cheese plant), banyan tree, sugarcane

Examples: aerial roots of banyan (support roots), root tubers of sweet potato (storage)

**Characteristic:** Develops from stem, leaves, or other unusual locations

Regions of the Root

The root tip has four distinct functional regions:

**1. Root Cap**

Thimble-shaped structure at root apex

Covered by multiple layers of cells

Protective function: shields tender apex as root pushes through soil

Cells continuously replaced as they wear away with friction

**2. Meristematic Region (Region of Cell Division)**

Located few millimetres above root cap

Contains actively dividing cells with small size, thin walls, and dense cytoplasm

Cells constantly undergoing mitosis (cell division)

**Exam Point:** This is the growth center of the root; no cell elongation occurs here

**3. Region of Elongation (Stretching Zone)**

Proximal (above) to meristematic region

Cells undergo rapid elongation and enlargement (cell expansion without division)

Responsible for primary growth in root length

Cells increase 500-1000 times their original size

**Duration:** Extends roughly 1 cm from meristematic region

**4. Region of Maturation (Differentiation Zone)**

Proximal to elongation region

Cells cease elongation and begin differentiation

Epidermal cells form delicate, thread-like **root hairs**

Root hairs are extensions of epidermal cells; increase surface area for absorption

Cells mature into specialized tissues (xylem, phloem, cortex)

**Exam Point:** Root hairs are single-celled, short-lived, and site of mineral absorption

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THE STEM

**Definition:** The stem is the aerial (above-ground), ascending part of the plant axis that develops from the plumule of the seed embryo. It bears branches, leaves, flowers, and fruits.

**Characteristic Features Distinguishing Stem from Root:**

**Growth direction:** Stem grows upward (positive geotropism), root grows downward

**Leaf bearing:** Stem bears leaves and leaf buds; root does not

**Chlorophyll:** Stem is green when young (can photosynthesize); root is non-green

**Nodes and internodes:** Stem has nodes (leaf attachment points) and internodes (distances between nodes); roots lack this pattern

**Color:** Young stem is green; root is typically white/pale

**Buds:** Terminal buds (apex) and axillary buds (leaf axils) present on stem; absent on root

**Main Functions of Stem:**

**Spreading:** Displays leaves, flowers, and fruits for photosynthesis, reproduction, and seed dispersal

**Conduction:** Transport of water and minerals (xylem) upward; food materials (phloem) downward

**Support:** Holds and positions leaves and reproductive structures toward light

**Storage:** Some stems store food (tubers like potato, rhizomes like ginger)

**Vegetative propagation:** Runners (strawberry), stolons (grass), offsets

**Protection:** Some modified stems are protective (thorns of acacia, spines of euphorbia)

**Structural Divisions:**

**Node:** Region where leaves and axillary buds are attached

**Internode:** Region between two successive nodes (without leaf attachment)

**Terminal bud:** Growing point at stem apex

**Axillary bud:** Bud in the axil of leaf (angle between petiole and stem); develops into branch

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THE LEAF

**Definition:** A leaf is a lateral, generally flattened vegetative structure borne on the stem at nodes. It is the primary organ of photosynthesis and develops from shoot apical meristems in acropetal order (youngest at apex, oldest toward base).

**General Characteristics:**

**Photosynthetic function:** Primary site of photosynthesis in plants

**Position:** Lateral appendage of stem

**Arrangement:** Develops at nodes in acropetal succession

**Dorsiventral structure:** Upper surface (adaxial/ventral) and lower surface (abaxial/dorsal)

Structure of a Typical Leaf

A complete leaf has three main parts:

**1. Leaf Base**

Point of attachment of leaf to stem

In dicots: remains small

In monocots: expands into **sheath** that wraps around stem partially or completely

In some legumes (pulvinate leaves): swollen into **pulvinus** structure (responds to touch, e.g., Mimosa)

**Function:** Attachment and sometimes movement

**2. Petiole (Leaf Stalk)**

Slender, stalk-like structure connecting leaf base to lamina

**Functions:**

Positions leaf blade for optimal light exposure

Long, thin, flexible petioles allow leaf to flutter in wind (increases air circulation, reduces heat, cooling effect)

In some plants modified into **phyllodia** (flattened petioles, e.g., Acacia) that perform photosynthesis

May develop **pulvini** at joints for movement responses

**Exam note:** Sessile leaves lack petiole and attach directly to stem

**3. Lamina (Leaf Blade)**

Flat, expanded green photosynthetic portion of leaf

Contains **network of veins and veinlets** for transport and support

**Midrib:** Prominent central vein running through lamina

**Features that vary by species:** Shape (oval, linear, cordate), margin (entire, serrated, lobed), apex (acute, obtuse, retuse), surface texture (smooth, hairy)

**Incisions:** Leaf margin may be deeply cut; if cuts do not reach midrib = simple leaf; if reach midrib = compound leaf

**Accessory Structures:**

**Stipules:** Pair of small, leaf-like structures at leaf base found in some plants (e.g., pea, rose); absent in many (e.g., grasses, palms)

**Function of stipules:** Protection of leaf during development, photosynthesis, storage

Venation

**Definition:** Arrangement pattern of veins and veinlets within the leaf lamina.

**Type 1: Reticulate (Net-like) Venation**

Veins and veinlets form an irregular network (reticulate = net-like)

Characteristic of **dicotyledonous plants**

Examples: mustard, mango, rose, hibiscus

**Advantage:** Strong, rigid structure; supports large leaf blades; efficient nutrient transport across network

Also called net venation or network venation

**Type 2: Parallel Venation**

Veins run parallel to each other throughout lamina

Do not form a network; run from leaf base to apex

Characteristic of **monocotyledonous plants**

Examples: wheat, rice, sugarcane, grasses, banana, coconut

**Advantage:** Graceful appearance; suitable for narrow, elongated leaves

Types of Leaves

**Simple Leaves**

**Definition:** Lamina is entire (margin unbroken) or if incisions are present, they do not extend to the midrib

Lamina cannot be separated into distinct leaflets

**Axillary bud present** in leaf axil (between petiole and stem)

Examples: mango, neem, sunflower, hibiscus

**Variations in simple leaves:** Entire margin (hibiscus), toothed margin (raspberry), lobed margin (okra) – but cuts don't reach midrib

**Compound Leaves**

**Definition:** Lamina is deeply lobed such that incisions reach the midrib, breaking it into multiple separate leaflets

Composed of **leaflets** (individual blade portions) attached to a common axis

**No axillary bud in leaflet axil** (key distinguishing feature from simple leaves)

**Petiole** corresponds to main axis; **petiolule** = stalk of individual leaflet

Types:

**Type 1: Pinnately Compound Leaf**

Leaflets arranged on **rachis** (elongated common axis representing midrib)

Leaflets positioned on either side of rachis, arranged like feathers

Two patterns:

**Odd-pinnate (imparipinnate):** Terminal leaflet present; odd number of leaflets (e.g., neem with 6-8 pairs + terminal = 13-17 leaflets); **pinnately odd**

**Even-pinnate (paripinnate):** No terminal leaflet; even number of leaflets; leaflets in pairs

Examples: neem (imparipinnate), tamarind (paripinnate)

Also can be bipinnately or tripinnately compound with rachis subdividing further

**Type 2: Palmately Compound Leaf**

All leaflets attached at **single common point** = apex of petiole

Leaflets radiate outward like fingers of a hand from palm

No rachis; leaflets arranged in circular pattern

Each leaflet has its own petiolule

Examples: silk cotton (Bombax) with 5-7 leaflets, horse chestnut with 7-9 leaflets, lupine

Phyllotaxy

**Definition:** Phyllotaxy is the pattern, arrangement, or sequence in which leaves are positioned on the stem or branch. It ensures maximum light exposure with minimum shading.

**Three Main Types:**

**1. Alternate Phyllotaxy**

**Pattern:** Single leaf arises at each node; successive leaves positioned alternately on opposite sides of stem

Leaves arranged in 1/2, 1/3, 2/5 fractions (Fibonacci sequence in spirals)

Creates spiral arrangement along stem

**Examples:** China rose (Hibiscus), mustard, sunflower, cotton

**Advantage:** Leaves do not shade each other; maximum light utilization

**2. Opposite Phyllotaxy**

**Pattern:** Two leaves arise at each node, positioned directly opposite each other on stem

Leaves are in pairs; successive pairs perpendicular to previous pair (decussate arrangement)

**Examples:** Calotropis (milkweed), guava, oleander, mint

**Advantage:** Balanced structure; symmetrical appearance

**3. Whorled Phyllotaxy**

**Pattern:** Three or more leaves arise at single node, arranged in a circle (whorl) around stem

All leaves attached at same level around stem axis

**Examples:** Alstonia (Devil Tree) with 4-5 leaves per whorl, nerium

**Number varies:** Sometimes called **decussate** if 4 leaves; **ternate** if 3 leaves

**Advantage:** Radial distribution; uniform light exposure

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THE INFLORESCENCE

**Definition:** Inflorescence is the arrangement of flowers on the floral axis (flowering stem). It refers to the mode and sequence of flower development on a plant.

**Floral Nature of Inflorescence:**

A **flower** is a modified shoot where shoot apical meristem transforms to **floral meristem**

Internodes do not elongate (condensed axis)

Apex produces floral appendages (sepals, petals, stamens, carpels) laterally instead of leaves

When shoot apex transforms into a single flower = always **solitary**

Two Major Types of Inflorescence

**Type 1: Racemose Inflorescence**

**Main Characteristics:**

Main axis (primary axis) **continues to grow indefinitely** (acropetal growth)

Flowers develop **laterally** on the main axis

Flowers arranged in **acropetal succession** (oldest flowers at base; youngest at apex)

Terminal flower never develops (apex remains vegetative)

**Indeterminate growth** = flowering continues from apex

**Common Examples:**

**Raceme:** Single main axis, pediceled flowers in acropetal order (e.g., mignonette, polyanthus)

**Spike:** Like raceme but flowers are **sessile** (no pedicel), e.g., wheat, turmeric, celosia

**Corymb:** Flowers at different heights on pedicel of different lengths; top becomes flat (e.g., candytuft, kalanchoe)

**Umbel:** All pedicels arise from **single point** at apex (like umbrella); flowers at same level (e.g., onion, carrot, parsnip)

**Catkin:** Pendant (hanging) raceme of unisexual flowers, usually male (e.g., willow, poplar, birch, oak, elm)

**Spadix:** Fleshy axis with small flowers crowded on it, often enclosed in **spathe** (e.g., arum, calla lily, maize male inflorescence)

**Cyme:** Modified raceme with flattened top (e.g., poinsettia)

**Type 2: Cymose Inflorescence**

**Main Characteristics:**

Main axis **terminates in a flower** (limited growth)

**Determinate growth** = apical meristem converts to floral meristem early

Flowers arranged in **basipetal succession** (youngest at base; oldest at apex/center)

Growth continues laterally from axillary buds, creating branching pattern

**Common Examples:**

**Simple Cyme (Monochasial):** Main axis terminates in flower; one lateral branch from below terminal flower; limited branching (e.g., sunflower's disc florets)

**Dichasial Cyme:** Terminal flower flanked by two lateral branches (dichotomous branching), forming characteristic "Y" shape with each branch repeating pattern (e.g., jasmine, chickpea, Silene)

**Polychasial Cyme:** Multiple lateral branches from below terminal flower (e.g., some celosias)

**Growth Pattern:** Branches repeat the process, creating pyramidal or flat-topped form

**Exam Distinction:** Racemose = main axis continues growing (indeterminate); Cymose = main axis ends in flower (determinate)

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THE FLOWER

**Definition:** A flower is the reproductive unit of angiosperms (flowering plants) specialized for sexual reproduction. It is a modified shoot where leaves are replaced by floral organs.

**Basic Structure:** A typical flower consists of four whorls of modified leaves (floral appendages) arranged concentrically on a swollen axis called **thalamus** (receptacle).

Floral Whorls and Their Arrangement

**Whorl 1: Calyx (Sepals)**

Outermost protective whorl

Made of modified leaves called **sepals**

Generally green, leaf-like, and collectively protect flower during bud stage

**Types:**

**Gamosepalous:** Sepals united/fused together

**Polysepalous:** Sepals free/separate

Examples of numbers: trimerous (3 sepals), tetramerous (4), pentamerous (5)

**Whorl 2: Corolla (Petals)**

Made of modified leaves called **petals**

**Functions:**

Bright colors and patterns attract pollinating insects (visual signals)

Sometimes fragrant (olfactory attraction)

Enclose and protect reproductive organs

**Characteristics vary greatly:**

**Types by fusion:** **Gamopetalous** (petals fused) or **Polypetalous** (petals free)

**Shapes:** Tubular (trumpet), bell-shaped, funnel-shaped, wheel-shaped (rotate), boat-shaped

**Numbers:** Usually 4-5 in dicots; 3 or multiples of 3 in monocots

**Examples:** Rose (fused), sunflower ray florets (tube), datura (funnel-shaped), hibiscus (rotate)

**Whorl 3: Androecium (Stamens)**

Male reproductive organs

Stamens collectively called androecium

Positions: Below or at same level as gynoecium in hypogynous/perigynous flowers; or surrounding ovary in epigynous flowers

**Whorl 4: Gynoecium (Carpels)**

Female reproductive organs

Carpels collectively called gynoecium

Position determines flower type (hypogynous, perigynous, epigynous)

Flower Types by Reproductive Organs

**Bisexual (Hermaphrodite) Flowers**

Contain **both androecium and gynoecium**

Both male and female organs functional

Examples: mustard, hibiscus, sunflower disc florets, tomato

**Unisexual Flowers**

Contain **either only stamens (male) or only carpels (female)**, not both

Male flowers with androecium only (no gynoecium)

Female flowers with gynoecium only (no androecium)

**Monoecious plants:** Both male and female flowers on same plant (e.g., maize, coconut, castor)

**Dioecious plants:** Male and female flowers on different plants (e.g., papaya, date palm, ginkgo)

Symmetry in Flowers

**Actinomorphic (Radially Symmetric) Flower**

**Definition:** Can be divided into **two equal halves** by any radial plane passing through the center

Looks the same from all angles when viewed from above

**Examples:** Mustard, datura (thorn apple), chilli, hibiscus, sunflower, lily

Also called **regular flower**

**Exam tip:** Most common type in dicots

**Zygomorphic (Bilaterally Symmetric) Flower**

**Definition:** Can be divided into **two similar halves by only ONE particular vertical plane** (left-right division only)

Distinct "upper" and "lower" surfaces; bilateral symmetry

**Examples:** Pea, bean, gulmohur, Cassia, orchids, snapdragon

Also called **irregular flower**

**Exam tip:** Common in legumes (Fabaceae); adapted for specific insect pollinators

**Asymmetric (Irregular) Flower**

**Definition:** Cannot be divided into **two similar halves** by any vertical plane passing through center

Completely irregular shape

**Examples:** Canna lily, some begonias

**Rarest type**

Floral Appendages: Numbers and Terminology

**Merous Flowers** (describe number of floral parts per whorl):

**Trimerous:** Floral parts in multiples of 3 (3, 6, 9) – typical of monocots (e.g., lily, tulip)

**Tetramerous:** Floral parts in multiples of 4 (4, 8) – some dicots (e.g., mustard with 4 petals, 6 stamens)

**Pentamerous:** Floral parts in multiples of 5 (5, 10) – common in dicots (e.g., hibiscus, rose)

**Bracts and Bracteoles:**

**Bract:** A modified leaf-like structure found at the base of pedicel (flower stalk)

**Bracteate flower:** Has bract present at pedicel base (e.g., sunflower)

**Ebracteate flower:** Lacks bract (e.g., hibiscus, mustard)

Position of Floral Parts (Flower Types by Ovary Position)

The relative position of calyx, corolla, and androecium with respect to the ovary determines flower classification:

**1. Hypogynous Flower (Superior Ovary)**

**Position:** Gynoecium (ovary) occupies the **highest position**

Calyx, corolla, and androecium are **below the ovary** on thalamus

**Ovary type:** **Superior ovary** = free above other parts; easily removed from flower

**Thalamus:** Flat or slightly convex

**Advantages:** Ovule protection; easy seed dispersal as fruit detaches easily

**Examples:** Mustard, china rose, brinjal, chilli, hibiscus, tomato, lily

**Diagram:** Sepal, petal, stamen progressively higher; ovary at top

**Most common type**

**2. Perigynous Flower (Half-Inferior Ovary)**

**Position:** Gynoecium (ovary) is **centrally placed**; calyx, corolla, and androecium are **at the rim** of thalamus

All flower parts are attached **at the same level** around the ovary

**Ovary type:** **Half-inferior ovary** = partially embedded in thalamus

**Thalamus:** Cup or saucer-shaped, surrounding the ovary

**Examples:** Plum, rose, peach, almond, strawberry, cherry, apple

**Fruit types:** Accessory fruits where thalamus develops into fleshy portion (e.g., apple has fleshy thalamus + core from carpel)

**3. Epigynous Flower (Inferior Ovary)**

**Position:** **Margin of thalamus grows upward**, enclosing the ovary completely

Thalamus becomes **fused with ovary wall**

Calyx, corolla, and androecium arise **above the ovary**

**Ovary type:** **Inferior ovary** = completely enclosed; no separation between ovary and thalamus

**Visual feature:** Sepals and petals appear to arise from top of fruit; ovary not visible from outside

**Examples:** Guava, cucumber, pumpkin, melon, sunflower (ray and disc florets), orchids, members of Cucurbitaceae and Asteraceae families

**Significance:** Ovary protection but harder seed/fruit dispersal

Parts of a Flower (Detailed Structure)

#### Calyx (Sepals)

**Structure and Function:**

Composed of green, leaf-like modified leaves called **sepals**

**Numbers:** Usually equal to petals; commonly 4-5 in dicots; 3 or 6 in monocots

**Color:** Predominantly green (chlorophyll present); sometimes colored or red

**Fusion Types:**

**Gamosepalous/Monosepalous:** Sepals united; single unit with lobes (e.g., Calotropis, datura, hibiscus)

**Polysepalous:** Sepals free; easily separable (e.g., mustard, rose, ranunculus)

**Functions:**

**Bud protection:** Enclose and protect young flower parts during development

**Support:** Hold and position developing flower

**Sometimes photosynthetic:** Contain chlorophyll; perform photosynthesis (green sepals)

**Nectary function:** Some sepals secrete nectar attracting pollinators

#### Corolla (Petals)

**Structure and Function:**

Composed of **petals** = modified, often highly specialized leaves

**Colors:** Highly variable – red, blue, pink, yellow, white, orange, purple (attract pollinating insects)

**Fragrances:** Many petals produce volatile compounds (perfume) increasing attractant value

**Patterns:** Spots, stripes, lines guide insects to nectaries

**Corolla Shape Variations:**

**Tubular/Tube-shaped:** Petals fused into cylindrical tube (e.g., hibiscus, datura)

**Bell-shaped:** Fused petals form bell cavity (e.g., morning glory)

**Funnel-shaped:** Petals fused into gradual funnel opening (e.g., datura, petunia)

**Wheel-shaped/Rotate:** Petals fused at base; spread open radially like wheel (e.g., potato, tomato)

**Boat-shaped:** Compact boat-like shape

**Papilionaceous:** Complex boat shape with distinct components (standard, wings, keel) – typical of pea family

**Fusion Types:**

**Gamopetalous/Monopetalous:** Petals fused into single structure with lobes (e.g., hibiscus, datura, Calotropis)

**Polypetalous:** Petals free; easily separable (e.g., mustard, rose, hibiscus types)

**Important Concept – Aestivation (Estivation):**

**Definition:** Aestivation is the **mode/pattern of arrangement of sepals or petals in the floral bud** with respect to other members of the same whorl. It describes how sepals/petals overlap before flower opens.

**Four Main Types:**

**1. Valvate Aestivation**

**Pattern:** Sepals or petals **just touch at margins** without overlapping

Edges meet edge-to-edge; no overlap

**Examples:** Calotropis (milkweed), datura, calyx of many flowers

**Appearance in bud:** Straight lines between parts; clean edges

**Advantage:** Easy opening of flower; minimal mechanical stress

**2. Twisted (Contorted) Aestivation**

**Pattern:** **One margin of appendage overlaps** the margin of next appendage; next overlaps the one beyond; creates spiral/twisted arrangement

Each part overlaps exactly one other in one direction (clockwise or counterclockwise spiral)

**Examples:** China rose (hibiscus), lady's finger (okra), cotton, morning glory, petunia

**Appearance:** Overlapping in obvious spiral fashion; petals can be individually separated showing overlap

**Common type**

**3. Imbricate Aestivation**

**Pattern:** **Margins of sepals or petals overlap one another** but **not in any particular direction** or regular sequence

Multiple overlaps; no organized spiral; random overlapping arrangement

**Examples:** Cassia, gulmohur (Delonix), Magnolia, some roses

**Appearance:** Complex overlapping without clear pattern; some parts completely enclosed, some partially exposed

**Common in dicots**

**4. Vexillary (Papilionaceous) Aestivation**

**Unique pattern:** Specific to pea family (Fabaceae) flowers with 5 petals

**Arrangement:**

**Standard (banner):** Largest petal; **overlaps two lateral petals**

**Wings:** Two lateral petals in middle; **overlap two smaller anterior petals**

**Keel:** Two smallest anterior petals; **completely enclosed by other petals**

Creates characteristic pea flower structure

**Examples:** Pea, bean, gulmohur, Cassia (some species), clovers

**Advantage:** Specialized shape for bee pollination; guides bee to nectar

**Exam Point:** Aestivation is used for plant classification and identification; observed in mature buds before flower opens.

#### Androecium (Stamens)

**Definition:** Androecium is the male reproductive whorl made of **stamens**. Each stamen is a male reproductive organ.

**Structure of a Stamen:**

**Two main parts:**

**Filament:** Thin, hair-like stalk; usually greenish or white; elevates anther

**Anther:** Terminal, pollen-bearing structure; usually bilobed (two lobes)

**Anther Structure (Pollen-Sac Location):**

**Bilobed anther:** Two lobes connected by **connective tissue**

**Four pollen-sacs:** Each lobe contains 2 chambers = 4 pollen-sacs per anther

**Pollen grains:** Produced in these sacs; released when anther matures

**Connective tissue:** Tissue connecting the two anther lobes; sometimes elongated (as in Salvia)

**Sterile Structures:**

**Staminode:** A stamen-like structure that is **sterile** (does not produce pollen); sometimes functions in pollination mechanism (e.g., Salvia, some orchids)

**Androecium Variations – Stamen Attachment:**

**1. Insertion on Flower Parts**

**Epipetalous:** Stamens attached/fused to **petals** (e.g., brinjal, hibiscus, datura, tomato)

**Epiphyllous:** Stamens attached to **perianth** (undifferentiated calyx/corolla); used when calyx and corolla are not distinct (e.g., lily, tulip)

**Hypogynous:** Stamens attached to thalamus (directly or below ovary); free from other parts

**2. Fusion Between Stamens (Androdynmous Arrangements)**

**Polyandrous:** All stamens **remain free/separate**; independent anthers (e.g., hibiscus, rose, buttercup)

**Monoadelphous:** Stamens **united into one bundle** (one group); filaments fused; anthers free (e.g., china rose, hibiscus, okra, sunflower)

**Diadelphous:** Stamens **united into two bundles** (two groups); typically 9+1 arrangement (e.g., pea, bean, many legumes)

**Polyadelphous:** Stamens **united into more than two bundles** (multiple groups); (e.g., citrus, St. John's wort)

**3. Variation in Stamen Length (Heteranthery)**

**Different filament lengths** within same flower

**Examples:**

**Mustard:** 4 stamens with 2 short and 2 long filaments

**Salvia:** Elongated connective tissue; stamens of different heights; 2 fertile and 2 sterile

**Function:** Prevents self-pollination (anther and stigma at different heights when flower opens); promotes cross-pollination

**Androcium Diversity Exam Points:**

Number of stamens varies: dimerous (2), trimerous (3), tetramerous (4), pentamerous (5), many (polyandrous)

Fusion patterns important for family classification (Fabaceae = diadelphous; Malvaceae = monoadelphous)

#### Gynoecium (Carpels/Pistil)

**Definition:** Gynoecium is the female reproductive whorl made of **carpels** (also called **pistil** when referring to entire female structure). Each carpel is a modified leaf-like structure specialized for reproduction.

**Structure of a Carpel:**

**Three main parts** (from base to apex):

**Ovary:** Enlarged, basal portion; contains ovules

**Style:** Elongated, tubular structure; connects ovary to stigma

**Stigma:** Terminal receptive surface; receives pollen grains

**Detailed Structure Breakdown:**

**Ovary**

Basal, swollen portion of carpel

**Unilocular:** Single chamber (compartment); e.g., pea, mustard

**Bilocular:** Two chambers; e.g., lemon, tomato

**Multilocular:** Multiple chambers; e.g., hibiscus, okra

**Ovule attachment:** Contains **placenta** (cushion-like tissue); ovules attached to placenta

**Number of ovules:** Varies from 1 (sunflower) to many (tomato, hibiscus)

**Style**

Tubular, stalk-like structure arising from ovary top

**Variable length:** Short (barely visible) to very long (extending beyond stamens