Families of Flowering Plants

Why plants are grouped into families

There are over 300,000 kinds of flowering plants. To study them, botanists group those that share many features, mainly in the flower, fruit and seed, into a family. A family name often ends in -aceae, for example Brassicaceae (also called Cruciferae). Flowering plants are first split into dicots (two seed leaves, net veins) and monocots (one seed leaf, parallel veins). Most of the families below are dicots; lily and grass are monocots.

Four floral parts to look at: calyx (sepals), corolla (petals), androecium (stamens, male) and gynoecium (pistil, female).

Mustard family (Cruciferae / Brassicaceae)

• 4 sepals and 4 petals arranged like a cross (the name cruciferae means cross-bearing).
• 6 stamens: 4 long and 2 short.
• Fruit: a long thin pod called a siliqua (a short one is a silicula).
• Often a sharp taste from sulphur compounds.
• Examples: mustard, cabbage, cauliflower, radish, turnip, broccoli.
• Uses: vegetables and mustard oil.

Pea family (Fabaceae, the legumes)

• Butterfly-shaped flower: 1 big standard petal at the back, 2 wings at the sides and 2 petals joined as a keel in front.
• Usually 10 stamens, many joined together.
• Fruit: a pod (legume) that splits along two seams.
• Root nodules contain Rhizobium bacteria that turn nitrogen from the air into a form the plant can use. This enriches the soil, so farmers grow legumes between cereal crops.
• Examples: pea, gram, bean, lentil, groundnut, soybean.
• Uses: pulses are rich in protein.

Rose family (Rosaceae)

• 5 sepals, 5 separate petals, and many stamens.
• Leaves often have toothed edges with small leaf-like parts at the base.
• Fruits are varied: a fleshy apple, a stone fruit like plum, or strawberry.
• Examples: rose, apple, pear, plum, peach, strawberry.
• Uses: fruits and ornamental flowers.

Potato family (Solanaceae, nightshades)

• 5 petals joined into a bell, funnel or star.
• 5 stamens attached to the petals.
• Fruit: a berry (tomato, brinjal, chilli) or a capsule (tobacco).
• Many members contain strong chemicals, some poisonous (the green parts of potato, datura).
• Examples: potato (the tuber is a stem), tomato, brinjal, chilli, tobacco, petunia.

Daisy family (Asteraceae)

• The "flower" is a head (capitulum) of many tiny flowers called florets held by a ring of green bracts.
• Ray florets on the edge look like petals. Disc florets in the middle are tiny tubes.
• Fruit: a small dry one-seeded fruit, often with a parachute of hairs.
• It is the largest family of flowering plants, so a single head gives many chances for pollination.
• Examples: sunflower, marigold, daisy, zinnia, lettuce, safflower.

Lily family (Liliaceae) and grass family (Poaceae)

Lily family (monocots): flower parts in threes, 6 similar tepals (petals and sepals look alike), 6 stamens, leaves with parallel veins, and often a bulb under the ground. Examples: lily, tulip, aloe; onion and garlic were traditionally placed here, but newer books place them in a close family.

Grass family (monocots): small flowers in spikelets with scale-like bracts, no showy petals, 3 stamens that hang out, feathery stigmas, wind pollination, and a dry fruit called a grain. Examples: wheat, rice, maize, barley, sugarcane, bamboo. Grasses feed most of the world.

Try it: sort a market basket

Collect or look at 8 flowers or vegetables: for example mustard, pea, tomato, marigold, grass, rose. Count the petals and stamens. Look at the fruit. Put each in a family and say which feature helped you. Then use the 3D free play to check your answers.

Key formulas and definitions

• Key terms: calyx (sepals), corolla (petals), androecium (stamens), gynoecium (pistil)
• Cruciferae: 4 petals in a cross, 6 stamens (4 + 2), siliqua
• Fabaceae: butterfly flower (1 + 2 + 2 petals), pod, root nodules
• Rosaceae: 5 separate petals, many stamens; Solanaceae: joined petals, 5 stamens, berry
• Asteraceae: head of ray and disc florets; Liliaceae and Poaceae: monocots

Worked examples

Common mistakes

• Saying a sunflower is one flower. It is a head of many tiny flowers.
• Mixing up the pea and mustard flowers. Pea is butterfly-shaped, mustard is cross-shaped.
• Thinking the potato tuber is a root. It is a swollen underground stem.
• Saying grasses have no flowers. They have small flowers without showy petals.