Flowering Plants

The One Thing

Flowering plants are identified and classified by examining the form, function and arrangement of their vegetative and reproductive organs. Reliable classification uses several characteristics together, especially seed type, cotyledon number, root system, leaf venation, floral parts and stem vascular-bundle arrangement.

Reactions, Processes and Experiments

Key Terms

• Angiosperms: Flowering plants whose ovules are enclosed in an ovary and whose seeds are enclosed in fruits.
• Root: The usually underground organ that anchors the plant, absorbs water and minerals, and may store food.
• Tap root system: A root system with one main primary root and smaller lateral roots, commonly found in dicot plants.
• Fibrous root system: A cluster of many thin roots arising from the base of the stem, commonly found in monocot plants.
• Stem: The supporting axis that bears leaves, flowers and buds and transports water, minerals and prepared food.
• Node: A point on the stem from which leaves, branches or buds arise.
• Internode: The portion of the stem between two successive nodes.
• Leaf: A usually green, flattened organ that performs photosynthesis, transpiration and gaseous exchange.
• Petiole: The stalk that attaches a leaf blade to the stem.
• Lamina: The broad, flat part of a leaf containing veins and performing most photosynthesis.
• Venation: The arrangement of veins and veinlets in the leaf blade.
• Reticulate venation: A net-like vein arrangement, usually characteristic of dicot leaves.
• Parallel venation: Veins that run nearly parallel to one another, usually characteristic of monocot leaves.
• Inflorescence: The arrangement of flowers on the floral axis.
• Flower: The reproductive structure of an angiosperm, made up of modified leaves arranged around a central axis.
• Calyx: The outermost floral whorl, made of sepals, which usually protects the flower bud.
• Corolla: The whorl of petals, often brightly coloured or scented to attract pollinators.
• Androecium: The male reproductive whorl of a flower, made up of stamens.
• Stamen: The male reproductive unit consisting of a filament and anther; the anther produces pollen grains.
• Gynoecium: The female reproductive whorl of a flower, made up of one or more carpels.
• Carpel or pistil: The female reproductive unit consisting of stigma, style and ovary.
• Stigma: The sticky upper part of the carpel that receives pollen grains.
• Style: The slender stalk connecting the stigma to the ovary.
• Ovary: The swollen basal part of the carpel containing ovules; it develops into the fruit after fertilisation.
• Ovule: A structure inside the ovary that contains the female gametophyte and develops into a seed after fertilisation.
• Complete flower: A flower having all four floral whorls: calyx, corolla, androecium and gynoecium.
• Bisexual flower: A flower containing both stamens and carpels.
• Unisexual flower: A flower containing either stamens or carpels, but not both.
• Actinomorphic flower: A flower that can be divided into two equal halves through more than one vertical plane; it is radially symmetrical.
• Zygomorphic flower: A flower that can be divided into two equal halves through only one vertical plane; it is bilaterally symmetrical.
• Aestivation: The arrangement of sepals or petals in a floral bud.
• Placentation: The arrangement of ovules within the ovary.
• Fruit: The mature ovary, sometimes together with other floral parts, usually containing seeds.
• Seed: The mature ovule containing an embryo, stored food and a protective seed coat.
• Monocotyledon: A flowering plant whose seed usually has one cotyledon.
• Dicotyledon: A flowering plant whose seed usually has two cotyledons.
• Cotyledon: An embryonic leaf in a seed that may store food or transfer stored food to the developing embryo.
• Classification: The systematic grouping of organisms based on shared characteristics and differences.
• Pedicellate flower: A flower with a stalk.
• Sessile flower: A flower without a stalk.
• Hypogynous flower: A flower in which the other floral parts arise below the ovary and the ovary is superior.
• Epigynous flower: A flower in which the other floral parts appear above the ovary and the ovary is inferior.
• Perigynous flower: A flower in which the floral parts arise around the ovary and the ovary is generally half-inferior.
• Pollination: The transfer of pollen grains from the anther to the stigma.
• Fertilisation: The fusion of male and female gametes.
• Floral formula: A symbolic representation of floral symmetry, sex, whorls, ovary position and fusion of parts.
• Floral diagram: A diagrammatic representation of floral structure, including symmetry, sex, whorls, ovary position and fusion of parts.

Easily Confused

• Tap root system vs fibrous root system: A tap root system has one main primary root with lateral roots; a fibrous root system consists of many thin roots arising from the stem base.
• Simple leaf vs compound leaf: A simple leaf has one undivided lamina; a compound leaf has a lamina divided into leaflets.
• Reticulate venation vs parallel venation: Reticulate venation forms a net-like pattern and is usually dicot; parallel venation consists of nearly parallel veins and is usually monocot.
• Node vs internode: A node bears leaves, branches or buds; an internode is the stem portion between successive nodes.
• Calyx vs corolla: The calyx is the outer whorl of sepals; the corolla is the petal whorl.
• Androecium vs gynoecium: The androecium is the male whorl of stamens; the gynoecium is the female whorl of carpels.
• Stamen vs carpel or pistil: A stamen consists of a filament and anther and produces pollen; a carpel or pistil consists of stigma, style and ovary.
• Pollination vs fertilisation: Pollination transfers pollen from anther to stigma; fertilisation is the fusion of male and female gametes.
• Ovule vs seed: The ovule is inside the ovary before fertilisation; it develops into a seed after fertilisation.
• Ovary vs fruit: The ovary is the basal part of the carpel before maturation; it develops into the fruit after fertilisation.
• Monocotyledon vs dicotyledon: A monocot usually has one cotyledon, while a dicot usually has two.
• Actinomorphic vs zygomorphic: An actinomorphic flower has more than one plane of symmetry; a zygomorphic flower has only one.
• Complete vs bisexual flower: A complete flower has all four floral whorls; a bisexual flower has both stamens and carpels. These conditions are not identical.
• Hypogynous vs epigynous vs perigynous: Hypogynous flowers have a superior ovary, epigynous flowers have an inferior ovary, and perigynous flowers generally have a half-inferior ovary with floral parts around it.
• Monocot examples vs dicot examples: Maize, wheat, rice, grass, lily and onion are monocot examples; pea, gram, bean, rose, mustard, sunflower and mango are dicot examples.

What Gets Asked

• Identify a plant organ or its function: Questions may ask about absorption, support, photosynthesis, transpiration, gaseous exchange, reproduction or dispersal. Marks are lost by assigning a function to the wrong organ or ignoring the role of root hairs.
• Distinguish monocots from dicots: Questions may require comparison of cotyledons, roots, venation, floral-part number and stem vascular bundles. A common error is relying on only one characteristic when several should be considered together.
• Classify named examples: Maize, wheat, rice, grass, lily and onion should be associated with monocots; pea, gram, bean, rose, mustard, sunflower and mango with dicots. Marks are lost by reversing these groups.
• Interpret floral structure: Questions may test calyx, corolla, androecium, gynoecium, stamen, carpel, stigma, style, ovary and ovule. The main slip is confusing the male and female reproductive whorls or their component parts.
• Determine flower type: Questions may distinguish complete, bisexual, unisexual, actinomorphic and zygomorphic flowers, as well as pedicellate and sessile flowers. These categories should not be treated as equivalent; for example, complete refers to all four whorls, whereas bisexual refers to both reproductive sexes.
• Trace reproductive development: Questions may ask what happens after fertilisation or distinguish pollination from fertilisation. The required sequence is that pollen reaches the stigma during pollination, male and female gametes fuse during fertilisation, the zygote develops into the embryo, the ovule becomes the seed and the ovary becomes the fruit.