Lesson 6: Classification of Plants

In the figure : In the figure plant classification shows cryptogams and phanerogams, then the groups below them.

Rule 1: The kingdom Plantae — In the Five Kingdom system of Robert Whittaker (1969), Plantae are autotrophic eukaryotes with cell walls. They are autotrophic because they perform photosynthesis with chlorophyll, and they are the main food source for all other living things.

• Easy : Mango and rice plants make their own food, so they are autotrophs.
• Medium : A mushroom has no chlorophyll, so it is not an autotroph; it is not placed with Plantae.
• Exam-type : Bacteria lack a true nucleus, so they cannot be eukaryotes; hence not Plantae even if some photosynthesise.

Rule 2: Basis of classification — The criteria, in order: (1) presence or absence of organs (अवयव); (2) presence or absence of separate conducting tissues (वहनी ऊतक) for water and food; (3) whether the plant bears seeds; (4) whether the seeds are enclosed in a fruit; (5) the number of cotyledons (बीजपत्र) in the seed.

• Easy : Rice has seeds, but a fern has none.
• Medium : Pea seeds are inside pods (fruits); pine seeds are naked.
• Exam-type : Order of questions for a plant: organs? tissues? seeds? fruit? cotyledons? Each answer narrows the group, like a game of 20 questions.

Rule 3: Cryptogams and phanerogams — In 1883 Eichler divided Plantae into two subkingdoms: cryptogams (गुप्तबीजी), with no flowers, fruits or seeds, and phanerogams (प्रकटबीजी), with seeds. Phanerogams divide into gymnosperms and angiosperms, and angiosperms into monocots and dicots.

• Easy : Fern: cryptogam. Mango: phanerogam.
• Medium : Moss, algae and ferns are all cryptogams as none has seeds.
• Exam-type : From the tree: Plantae → phanerogams → angiosperms → dicots → mango.

Spot the difference

Rule 1: Thallophyta — Division I of the cryptogams. They grow mainly in water, have no specific root, stem, leaf or flower, and are autotrophic because of chlorophyll. This group is called algae.

• Easy : Spirogyra grows in ponds and has no root, stem or leaf.
• Medium : The slimy green layer on a pond is made of algae, which photosynthesise.
• Exam-type : Why are algae autotrophic even though they lack leaves? Because their cells have chlorophyll in chloroplasts.

Rule 2: Diversity of algae — Algae may be unicellular or multicellular, microscopic or large, and live in fresh or saline water. The body is usually soft and fibre-like. Examples: Spirogyra, Ulothrix, Ulva, Sargassum, Chara. Spirogyra has spiral green chloroplasts. Fungi such as yeasts and moulds, which have no chlorophyll, are also included in this group.

• Easy : Ulva (sea lettuce) lives in sea water; Spirogyra lives in fresh water.
• Medium : Algae can be a single cell (microscopic) or large like Sargassum seaweed.
• Exam-type : Yeast has no chlorophyll, so it is not autotrophic, yet the old system placed it in this group.

Spot the difference

In the figure : In the figure algae, mosses and ferns reproduce by spores.

Rule 1: Bryophyta — Bryophyta grow in moist soil but need water for reproduction, which is why they are the 'amphibians' of the plant kingdom. The body is thalloid, flat and ribbon-like, with stem-like and leaf-like parts and root-like rhizoids but no true root, stem or leaf, and no conducting tissue. They reproduce by spores. Examples: moss (Funaria), Marchantia, Anthoceros, Riccia.

• Easy : Moss grows on damp walls in the rains.
• Medium : Rhizoids are root-like, but they are not true roots.
• Exam-type : Bryophyta are called amphibians of the plant kingdom since they live on land but need water to reproduce, like frogs.

Rule 2: Pteridophyta — Pteridophyta have well-developed roots, stem and leaves and separate conducting tissues, but no flowers or fruits. Spores form in sporangia, in groups called sori on the back of the leaves. Asexual reproduction is by spores and sexual reproduction by zygote formation. Examples: ferns (Nephrolepis, Marsilea, Pteris, Adiantum), Equisetum, Selaginella, Lycopodium.

• Easy : A fern has real roots, stem and leaves; a moss does not.
• Medium : The brown dots under a fern leaf are sori holding sporangia.
• Exam-type : A plant with conducting tissue but no seeds or flowers is a pteridophyte; with no conducting tissue and a flat body, a bryophyte.

Rule 3: Cryptogams — Thallophyta, Bryophyta and Pteridophyta are cryptogams (cryptos: hidden, gams: reproductive organs). All reproduce by spores.

• Easy : Algae, mosses and ferns all multiply by spores.
• Medium : Cryptogams: 3 groups (Thallophyta, Bryophyta, Pteridophyta).
• Exam-type : Only pteridophytes among cryptogams have both conducting tissue and true organs.

Spot the difference

In the figure : In the figure gymnosperms have naked seeds and angiosperms have seeds inside fruits.

Rule 1: Phanerogams — Phanerogams have special reproductive structures and produce seeds that contain the embryo and stored food. They are divided by whether the seed is enclosed in a fruit.

• Easy : A seed holds a baby plant (embryo) and its food.
• Medium : Phanerogams are two groups: gymnosperms and angiosperms.
• Exam-type : A seed that is inside a fruit means the plant is an angiosperm.

Rule 2: Gymnosperms — Gymnosperms (gymnos: naked) are mostly evergreen, perennial and woody. The stem is unbranched with a crown of leaves. Male and female flowers are on different sporophylls of the same plant. Seeds have no natural covering and there are no fruits. Examples: Cycas, Picea (Christmas tree), Thuja, Pinus (Deodar).

• Easy : Cycas and Pinus are gymnosperms.
• Medium : A pine cone has seeds on its scales, open to the air, and no fruit around them.
• Exam-type : Gymnosperms are mostly woody and evergreen, so a tall tree that never sheds all leaves and has cones is likely a gymnosperm.

Rule 3: Angiosperms — Angiosperms (angios: cover) have flowers as reproductive organs. Flowers develop into fruits, and seeds form inside the fruits. Examples: hibiscus, lily, tamarind, mango.

• Easy : Hibiscus has flowers and later fruits with seeds.
• Medium : A mango fruit is the developed flower, and the seed is inside it.
• Exam-type : A rose, a lily and a tamarind all produce flowers, so all three are angiosperms.

Spot the difference

In the figure : In the figure dicots and monocots are compared.

Rule 1: Dicotyledons — Dicots have two cotyledons, so the seed splits into two equal halves. They have a primary tap root, a strong hard stem (as in banyan), reticulate venation, and flowers with 4 or 5 parts or their multiples (tetramerous or pentamerous). Examples: mustard, groundnut, tamarind, mango.

• Easy : Groundnut has two cotyledons, so it is a dicot.
• Medium : A flower with 5 petals and 5 sepals is pentamerous, so it is likely a dicot.
• Exam-type : A flower with 8 parts is a multiple of 4 (8 = 4 × 2), so it fits a dicot; one with 12 parts could be 4 × 3 or 3 × 4, so count other features too.

Rule 2: Monocotyledons — Monocots have one cotyledon. They have fibrous roots; the stem may be hollow (bamboo), a false stem (banana) or disc-like (onion). Venation is parallel, and flowers have 3 parts or multiples of 3 (trimerous). Examples: maize, wheat.

• Easy : Maize has parallel veins in its leaf, so it is a monocot.
• Medium : A flower with 6 parts (6 = 3 × 2) fits a monocot.
• Exam-type : Coconut has a fibrous root system, so it is a monocot. A mango has a tap root, so it is a dicot.

Spot the difference