Flower Structure — Revision Notes

⚡ 30-Second Revision

Flower — Reproductive shoot of angiosperms.
Whorls — Calyx (sepals), Corolla (petals), Androecium (stamens), Gynoecium (carpels).
Calyx — Protection (sepals: gamosepalous/polysepalous).
Corolla — Attraction (petals: gamopetalous/polypetalous).
Androecium — Male part (stamen = filament + anther).

- Cohesion: Monoadelphous (China rose), Diadelphous (Pea), Polyadelphous (Citrus). - Length: Didynamous (Salvia), Tetradynamous (Mustard).

Gynoecium — Female part (carpel = stigma + style + ovary + ovules).

- Carpels: Apocarpous (Rose, Lotus), Syncarpous (Mustard, Tomato).

Symmetry — Actinomorphic ($\oplus$, radial: Mustard, Datura), Zygomorphic ($\%$, bilateral: Pea, Gulmohur).
Ovary Position

- Hypogynous (Superior): Mustard, China rose, Brinjal. - Perigynous (Half-inferior): Plum, Rose, Peach. - Epigynous (Inferior): Guava, Cucumber, Sunflower (ray florets).

Aestivation — Arrangement of sepals/petals in bud.

- Valvate: Calotropis (touch without overlap). - Twisted: China rose, Cotton (regular overlap). - Imbricate: Cassia, Gulmohur (irregular overlap). - Vexillary: Pea, Bean (standard overlaps wings, wings overlap keel).

Placentation — Ovule arrangement in ovary.

- Marginal: Pea. - Axile: China rose, Tomato, Lemon. - Parietal: Mustard, Argemone. - Free Central: Dianthus, Primrose. - Basal: Sunflower, Marigold.

2-Minute Revision

The flower is the reproductive unit of angiosperms, essentially a modified shoot with condensed internodes. It consists of four main whorls: the outermost protective calyx (sepals), the attractive corolla (petals), the male reproductive androecium (stamens), and the female reproductive gynoecium (carpels).

Sepals and petals can be free (poly-) or fused (gamo-). Stamens comprise a filament and an anther, and can be fused into one (monoadelphous, e.g., China rose), two (diadelphous, e.g., Pea), or many bundles (polyadelphous, e.

g., Citrus). The gynoecium has a stigma, style, and ovary, with ovules inside. Carpels can be free (apocarpous, e.g., Rose) or fused (syncarpous, e.g., Mustard).

Floral symmetry can be radial (actinomorphic, e.g., Mustard) or bilateral (zygomorphic, e.g., Pea). The ovary's position relative to other parts defines it as superior (hypogynous, e.g., China rose), half-inferior (perigynous, e.

g., Plum), or inferior (epigynous, e.g., Guava). Aestivation describes how sepals/petals arrange in the bud (valvate, twisted, imbricate, vexillary). Placentation is the arrangement of ovules in the ovary (marginal, axile, parietal, free central, basal), each with specific examples like pea for marginal and tomato for axile.

Mastering these terms and their NCERT examples is crucial for NEET.

5-Minute Revision

The flower, the reproductive marvel of angiosperms, is a highly specialized shoot. Its structure is built upon four concentric whorls, each playing a vital role. The outermost calyx, made of sepals, primarily protects the bud.

Inside is the corolla, composed of often colorful petals, whose main function is to attract pollinators. Both sepals and petals can be free (polysepalous/polypetalous) or fused (gamosepalous/gamopetalous).

The arrangement of these parts in the bud is called aestivation, with types like valvate (margins touch, e.g., Calotropis), twisted (regular overlap, e.g., China rose), imbricate (irregular overlap, e.

g., Cassia), and vexillary (specialized overlap in pea family).

The essential reproductive whorls are the androecium and gynoecium. The androecium consists of stamens, each with a filament and an anther (pollen-producing part). Stamens can be fused in various ways: monoadelphous (one bundle, e.g., China rose), diadelphous (two bundles, e.g., Pea), or polyadelphous (many bundles, e.g., Citrus). Their lengths can also vary (e.g., didynamous, tetradynamous in mustard).

The innermost gynoecium (pistil) is the female part, comprising one or more carpels. Each carpel has a sticky stigma for pollen reception, a style for pollen tube growth, and an ovary containing ovules.

Carpels can be free (apocarpous, e.g., Rose) or fused (syncarpous, e.g., Mustard). A critical feature is placentation, the arrangement of ovules within the ovary. Key types include marginal (pea), axile (china rose, tomato), parietal (mustard, Argemone), free central (Dianthus), and basal (sunflower).

Flowers also exhibit symmetry: actinomorphic (radial, e.g., Mustard) or zygomorphic (bilateral, e.g., Pea). The ovary position relative to other floral parts is also important: hypogynous (superior ovary, e.g., China rose), perigynous (half-inferior, e.g., Plum), or epigynous (inferior ovary, e.g., Guava). Understanding these terms, their examples, and their functional significance is paramount for NEET.

Prelims Revision Notes

For NEET, a rapid recall of flower structure essentials is key. Remember the flower as a modified shoot, with the thalamus as its base. The four whorls are Calyx (sepals) for protection, Corolla (petals) for attraction, Androecium (stamens) for male reproduction, and Gynoecium (carpels) for female reproduction.

Aestivation (arrangement in bud):

Valvate — Margins touch, no overlap (e.g., *Calotropis*).
Twisted — Regular overlap (e.g., *China rose*, *Cotton*).
Imbricate — Irregular overlap (e.g., *Cassia*, *Gulmohur*).
Vexillary — Standard overlaps wings, wings overlap keel (e.g., *Pea*, *Bean*).

Stamen Cohesion:

Monoadelphous — Filaments in one bundle (e.g., *China rose*).
Diadelphous — Filaments in two bundles (e.g., *Pea*).
Polyadelphous — Filaments in many bundles (e.g., *Citrus*).
Didynamous — 4 stamens, 2 long + 2 short (e.g., *Salvia*).
Tetradynamous — 6 stamens, 4 long + 2 short (e.g., *Mustard*).

Gynoecium (Pistil): Stigma, Style, Ovary (with ovules).

Apocarpous — Free carpels (e.g., *Rose*, *Lotus*).
Syncarpous — Fused carpels (e.g., *Mustard*, *Tomato*).

Placentation (ovule arrangement):

Marginal — Along ventral suture (e.g., *Pea*).
Axile — Central axis, septate ovary (e.g., *China rose*, *Tomato*, *Lemon*).
Parietal — Inner wall, unilocular/false septum (e.g., *Mustard*, *Argemone*).
Free Central — Central axis, no septa (e.g., *Dianthus*, *Primrose*).
Basal — Single ovule at base (e.g., *Sunflower*, *Marigold*).

Ovary Position:

Hypogynous (Superior) — Other parts below ovary (e.g., *Mustard*, *China rose*, *Brinjal*).
Perigynous (Half-inferior) — Parts at rim of thalamus (e.g., *Plum*, *Rose*, *Peach*).
Epigynous (Inferior) — Parts above ovary (e.g., *Guava*, *Cucumber*, *Sunflower* ray florets).

Symmetry:

Actinomorphic ($\oplus$, Radial) — Divisible by any radial plane (e.g., *Mustard*, *Datura*, *Chilli*).
Zygomorphic ($\%$, Bilateral) — Divisible by only one plane (e.g., *Pea*, *Gulmohur*, *Bean*).

Remember the distinction: Complete flower (all 4 whorls) vs. Perfect/Bisexual flower (both androecium and gynoecium). All complete flowers are perfect, but not vice-versa. Monoecious (male & female flowers on same plant, e.g., maize) vs. Dioecious (male & female flowers on separate plants, e.g., papaya). Focus on NCERT examples for each category.

Vyyuha Quick Recall

To remember the types of Placentation and their examples:

My Peace Always Comes Through Prayer Morning And Free Day By Sun.

Marginal: Pea
Axile: China rose, Tomato
Parietal: Mustard, Argemone
Free Central: Dianthus
Basal: Sunflower