Brassicaceae Mustard Family: Floral Characters and Examples

Brassicaceae, earlier called Cruciferae, is the mustard family. It includes mustard, cabbage, cauliflower, radish, turnip, and rapeseed. Its flowers have four petals arranged like a cross, which is why the old name Cruciferae means cross-bearing.

This family is central to Indian farming and food. Mustard oil is a major cooking oil, the vegetables supply vitamins and fibre, and mustard cake left after oil extraction is used as cattle feed and manure.

Key Concepts

Plants are annual or biennial herbs with alternate leaves and often a pungent smell due to sulphur compounds. Inflorescence is typically a raceme without bracts.

• Calyx: 4 sepals in two whorls of 2 + 2, free.
• Corolla: 4 petals, free, cruciform with clawed bases.
• Androecium: 6 stamens in tetradynamous condition — 2 outer short and 4 inner long.
• Gynoecium: Bicarpellary, syncarpous, superior ovary, unilocular becoming bilocular due to a false septum called replum.
• Fruit: Siliqua or silicula. Seed: Non-endospermic.

Floral formula: ⊕ ⚥ K2+2 C4 A2+4 G(2).

How It Works

1. Four cross-shaped petals make flowers easy for insects to locate.
2. The tetradynamous stamens place pollen efficiently on pollinators.
3. After fertilisation, the ovary lengthens into a siliqua pod.
4. The replum holds seeds in a row, and the two valves split open to release them.

Worked Example

A mustard flower has 4 sepals + 4 petals + 6 stamens + 2 carpels = 16 floral parts. In a raceme of 30 flowers, stamens = 30 × 6 = 180, of which long stamens = 30 × 4 = 120 and short stamens = 30 × 2 = 60. The 4 long + 2 short pattern instantly confirms the tetradynamous condition.

Common Misconceptions

• Cauliflower we eat is a fruit: Wrong. The edible part is the condensed, fleshy inflorescence.
• Ovary is naturally bilocular from the start: Wrong. It starts unilocular and becomes bilocular by the replum.
• All 6 stamens are equal: Wrong. Brassicaceae is tetradynamous: 2 short outer and 4 long inner.

Real-World Applications

Mustard and rapeseed give edible oil, leaves are eaten as sarson ka saag, and radish, turnip, cabbage, cauliflower, and knol-khol are vegetables. Some species provide fodder, green manure, and condiments, making the family valuable in rabi cropping across India.

Four cruciform petals, tetradynamous stamens, replum, and siliqua fruit are the signature of Brassicaceae — the family behind mustard oil and winter vegetables.