Morphology of Flowering Plants

The Root

Root Types & Regions

• True/Tap Root: Originates from the radicle, characteristics of dicots (e.g., Mustard). Differentiated into primary, secondary, and tertiary roots.
• Fibrous Root: Primary root is short-lived; roots originate from the base of the stem NEET 2020 in monocots (e.g., Wheat).
• Adventitious Root: Originates from parts other than the radicle (e.g., Grass, Monstera, Banyan).
• Root Cap: Protects the tender apex as it penetrates the soil.
• Region of Meristematic Activity: Small, thin-walled cells with dense protoplasm that divide repeatedly.
• Region of Elongation: Rapid elongation and enlargement; responsible for the growth of the root in length.
• Region of Maturation: Cells differentiate and mature.

Crucial detail: Root hairs develop from the epidermal cells of the region of maturation NEET 2017.

Modifications of Root

• For Food Storage:
  • Tap roots: Fusiform (Radish), Conical (Carrot), Napiform (Turnip, Sugarbeet).
  • Adventitious roots: Tuberous (Sweet potato NEET 2018), Fasciculated (Asparagus, Dahlia).
• For Respiration: Pneumatophores grow vertically upwards (negatively geotropic) in marshy/swampy areas (halophytes) to get oxygen for respiration NEET 2018, AIPMT 2000, NEET 2022. Found in Rhizophora (Mangroves).
• For Nitrogen Fixation: Nodulated roots found in legume branches (e.g., Pea, Gram).
• For Support:
  • Prop roots (Pillar roots): Hanging roots from branches for support (e.g., Banyan).
  • Stilt roots: Arise from lower nodes of the stem to support the plant (e.g., Maize, Sugarcane).

Exceptions/Extra details: Roots play an insignificant role in water absorption in free-floating hydrophytes like Pistia AIPMT 2015. Velamen tissue for moisture absorption is found in the aerial roots of epiphytic orchids AIPMT 1991. The largest flower, Rafflesia, is a total root parasite AIPMT 1999.

The Stem

Characteristics & Functions

• Ascending part of the axis developing from the plumule. Bears nodes and internodes.

Crucial detail: Subaerially growing stems in grasses and strawberry help in vegetative propagation NEET 2022.

Modifications of Stem

• Underground Stem (Organ of Perennation/Food Storage):
  • Tuber: Swollen tips of branches with 'eyes' (axillary buds covered with scaly leaves) (e.g., Potato AIPMT 2014).
  • Rhizome: Horizontal fleshy stem with nodes/internodes (e.g., Ginger, Turmeric, Banana). Exception: Apical bud remains underground; does not grow aerially NEET 2022.
  • Corm: Condensed structure, grows vertically (e.g., Colocasia, Amorphophallus/Zaminkand, Saffron).
  • Bulb: Highly reduced disc-like stem surrounded by fleshy leaves storing food (e.g., Onion, Garlic).
• Sub-aerial Modification (Creeping Stems):
  • Runner: Roots at the lower side, leaves upper side of nodes (e.g., Doob grass, Oxalis, Strawberry).
  • Stolon: Branches from the lower part of the main stem grow like an arch and finally touch the ground (e.g., Jasmine, Peppermint).
  • Sucker: Main stem underground, branches grow obliquely upward (e.g., Mint, Pineapple, Chrysanthemum, Banana).
  • Offset: Aquatic runner with short internodes, each node bearing a rosette of leaves and a tuft of roots (e.g., Pistia, Eichhornia).
• Aerial Modification:
  • Stem Tendril: Axillary bud modified for climbing (e.g., Grapes, Gourds like cucumber, pumpkin, watermelon NEET 2022, AIPMT 2016).
  • Stem Thorn: Axillary bud modified into a woody, pointed, defensive organ (e.g., Citrus, Bougainvillea NEET 2022, NEET 2017, AIPMT 2016).
  • Phylloclade: Stem flattened and fleshy (e.g., Opuntia NEET 2022, AIPMT 2016) or cylindrical (e.g., Euphorbia) performing photosynthesis. Leaves are modified into spines AIPMT 2015.

The Leaf

Leaf Parts, Venation & Phyllotaxy

• Originates from shoot apical meristems, arranged in acropetal order. A bud is present in the axil of a simple or compound leaf petiole, but never in the axil of leaflets NEET 2022.
• Parts: Leaf base (Hypopodium), Petiole (Mesopodium), Lamina (Epipodium).

Crucial details: Sheathing leaf base is found in monocots. Pulvinus (swollen leaf base) is found in legumes. Stipules are lateral leaf-like structures at the base.

• Venation:
  • Reticulate: Found in dicots. Exception: Calophyllum has parallel.
  • Parallel: Found in monocots. Exception: Smilax has reticulate.
• Phyllotaxy:
  • Alternate: Single leaf per node (e.g., Mustard, China rose, Sunflower).
  • Opposite: Pair of leaves per node (e.g., Guava, Calotropis, Ocimum).
  • Whorled: More than two leaves per node forming a whorl (e.g., Alstonia AIPMT 2011, Nerium).

Simple vs Compound Leaves & Modifications

• Simple Leaf: Lamina entire or incised (but not up to the midrib).
• Compound Leaf: Lamina incised up to the midrib/petiole, dividing into leaflets.
  • Pinnately Compound: Leaflets present on a common axis, the rachis (e.g., Neem).
  • Palmately Compound: Leaflets attached at a common point at the tip of the petiole without a rachis (e.g., Silkcotton).
• Modifications:
  • Leaf Tendril: For climbing (e.g., Pea).
  • Leaf Spines: For defense/reducing water loss (e.g., Opuntia, Aloe).
  • Fleshy Leaves: For food storage (e.g., Onion, Garlic).
  • Phyllode: Petiole becomes flat, green, and photosynthetic (e.g., Australian acacia AIPMT 2012).
  • Insectivorous Leaves: Pitcher plant (Nepenthes - lamina modified AIPMT 2016), Venus Fly Trap (Dionaea - jaws close by rapid turgor pressure changes AIPMT 2005), Bladderwort (Utricularia AIPMT 2002, AIPMT 1999), Sundew (Drosera).

The Inflorescence

• Racemose: Main axis continues to grow, flowers in acropetal succession (e.g., Radish, Mustard).
  • Raceme: Pedicellate flowers.
  • Spike: Sessile flowers (e.g., Achyranthes).
  • Spadix: Fleshy peduncle with large bract (spathe). Found in Maize cob (silky hairs are modifications of styles AIPMT 2000).
  • Capitulum / Head: Flattened receptacle with Ray and Disc florets. Most advanced (e.g., Sunflower, Marigold NEET 2020).
• Cymose: Main axis terminates in a flower, limited growth, basipetal succession NEET 2024, NEET 2023. (e.g., Solanum NEET 2024, Bougainvillea, Jasmine).
• Hypanthodium: Fleshy pear-shaped receptacle with a pore (ostiole). Encloses male, female, and sterile flowers (e.g., Fig, Banyan, Peepal AIPMT 1994).

The Flower

Floral Symmetry & Thalamus Position

A flower is a modified shoot where the apical meristem changes to a floral meristem, and internodes condense NEET 2023.

• Actinomorphic (Radial): Divisible into two equal halves in any radial plane (e.g., Mustard/Brassica NEET 2024, AIPMT 2016, Datura, Chilli).
• Zygomorphic (Bilateral): Divisible in only one vertical plane (e.g., Pea, Bean, Gulmohar, Cassia AIPMT 2011).
• Asymmetrical: Cannot be divided equally (e.g., Canna).
• Insertion of Floral Leaves:
  • Hypogynous: Gynoecium is at the highest position NEET 2020. Ovary is Superior (e.g., Mustard, China rose, Brinjal, Potato, Onion, Tulip AIPMT 2015).
  • Perigynous: Thalamus grows upward forming a cup. Ovary is Half-inferior (e.g., Plum, Peach, Rose NEET 2024, NEET 2020, AIPMT 2011).
  • Epigynous: Thalamus completely encloses the ovary and fuses with it. Ovary is Inferior (e.g., Guava, Apple, Cucumber, Ray florets of sunflower NEET 2024, NEET 2020, AIPMT 2015).

Aestivation & Placentation (High-Yield Comparisons)

Aestivation Type	Characteristics	Examples (PYQs)
Valvate	Margins just touch without overlapping.	Calotropis NEET 2023, Solanaceae.
Twisted	One margin overlaps the next.	Cotton, China rose, Ladyfinger NEET 2024, AIPMT 2010.
Imbricate	Margins overlap but not in any particular direction.	Cassia, Gulmohar.
Vexillary	Posterior standard (vexillum) overlaps lateral wings, which overlap anterior fused keel (carina).	Pea, Bean (Fabaceae) NEET 2024, NEET 2023, AIPMT 2016.

Placentation Type	Characteristics	Examples (PYQs)
Marginal	Ridge along the ventral suture, ovules in two rows.	Pea NEET 2024.
Axile	Multilocular, ovules on the central axis.	China rose, Petunia, Lemon, Tomato NEET 2024, NEET 2023, AIPMT 2012.
Parietal	Unilocular but becomes bilocular due to false septum (replum). Ovules on inner/peripheral wall NEET 2019.	Mustard NEET 2024, AIPMT 2008, Argemone.
Free Central	Unilocular, ovules on the central axis without septa.	Primrose, Dianthus NEET 2024, AIPMT 2016, AIPMT 2012.
Basal	Single ovule attached at the base.	Sunflower, Marigold NEET 2024.

Androecium

• Cohesion of Stamens:
  • Monoadelphous: Single bundle (e.g., China rose NEET 2024).
  • Diadelphous: Two bundles, typically 9+1 arrangement (e.g., Pea NEET 2024, NEET 2021).
  • Polyadelphous: More than two bundles (e.g., Citrus NEET 2024, AIPMT 2016).
• Adhesion of Stamens:
  • Epipetalous: Attached to petals (e.g., Brinjal NEET 2024).
  • Epiphyllous / Epitepalous: Attached to the perianth (e.g., Lily NEET 2024).
• Length Variation: Didynamous (2 long, 2 short - Salvia), Tetradynamous (4 long inner, 2 short outer - Mustard, Radish, Turnip AIPMT 2016).

The Fruit & Seed

Fruit Types & Edible Parts

• True Fruit: Develops strictly from the ovary (e.g., Mango, Coconut).
• False Fruit: Develops from parts other than the ovary, like the thalamus (e.g., Apple, Strawberry, Pear, Cashew).
• Parthenocarpic Fruit: Develops without fertilization, seedless (e.g., Banana).
• Fleshy Fruits:
  • Drupe: From monocarpellary superior ovary AIPMT 2011. Stony endocarp. Edible part in Mango is Mesocarp AIPMT 2004. In Coconut, the endocarp is hard, mesocarp is fibrous, and the edible part is the cellular/nuclear Endosperm AIPMT 2009.
  • Berry: Fleshy with seeds embedded (e.g., Tomato - placenta and pericarp are edible AIPMT 2014).
  • Pome: False fruit with fleshy edible thalamus (e.g., Apple, Pear).
  • Balausta: From an inferior ovary, the succulent testa is edible (e.g., Pomegranate AIPMT 2008, AIPMT 2009).
• Aggregate Fruits: Develop from a multicarpellary, apocarpous gynoecium (e.g., Etaerio of achenes in Strawberry) AIPMT 2014.
• Composite Fruits: Develop from an entire inflorescence (e.g., Pineapple AIPMT 2006, Fig - syconus encloses achenes AIPMT 2008).

Seed Structure

• Dicot Seed: Two fleshy cotyledons. Plumule and radicle at the ends of the embryonal axis. Mostly non-endospermic (Gram, Pea), but Castor is endospermic.
• Monocot Seed: Usually endospermic (e.g., Maize, Wheat). Non-endospermic in Orchids.
  • Contains a massive proteinous Aleurone layer.
  • Single, large shield-shaped cotyledon called the Scutellum.
  • Plumule enclosed in Coleoptile, Radicle in Coleorhiza.

Plant Families

Family	Floral Formula	Key Identifying Features
Brassicaceae (Mustard)	⊕ ⚥ K2+2 C4 A2+4 G(2)	Actinomorphic, Tetramerous. Cruciform valvate petals. Tetradynamous stamens. Bicarpellary superior ovary with replum (false septum) and parietal placentation. Fruit: Siliqua.
Solanaceae (Potato)	⊕ ⚥ K(5) C(5) A5 G(2)	Actinomorphic, Pentamerous. Epipetalous stamens. Bicarpellary, obliquely placed superior ovary AIPMT 2001. Swollen axile placenta. E.g., Potato, Tomato, Brinjal, Atropa, Tobacco, Petunia.
Fabaceae (Pea)	% ⚥ K(5) C1+2+(2) A(9)+1 G1	Zygomorphic. Nodulated roots. Papilionaceous corolla (vexillary aestivation). Diadelphous stamens. Monocarpellary superior ovary, marginal placentation. Fruit: Legume. E.g., Pulses, Mulaithi, Indigofera.
Liliaceae (Lily)	Br ⊕ ⚥ P(3+3) A3+3 G(3)	Monocot, Actinomorphic, Trimerous. Perianth (Tepals 6). Epiphyllous stamens. Tricarpellary superior ovary, axile placentation. E.g., Onion, Garlic, Aloe vera, Tulip, Colchicum.

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