6. Classification of Plants

Explanation: thallophytes such as Spirogyra and Ulothrix grow mainly in water, which supports their body. Their body is not divided into root, stem and leaves, and has no hard or woody tissue, so it is soft and fibre-like (thread-like).

Explanation: amphibians like the frog live on land but need water to reproduce. In the same way, bryophytes such as moss and Riccia grow on moist soil, walls and rocks, but they need water for reproduction.

Explanation: ferns and other pteridophytes produce spores in sporangia, arranged in sori on the underside of their leaves. Each spore can grow into a new plant; this is asexual reproduction. In the sexual stage, male and female gametes fuse to form a zygote, which develops into the new fern plant.

Explanation: in gymnosperms such as Cycas and Pinus, the reproductive structures are special leaves called sporophylls, grouped into cones. Male sporophylls produce pollen and female sporophylls bear naked ovules, which develop into seeds without any fruit covering.

• Phanerogams have special, clearly visible structures for reproduction (flowers or cones).
• After reproduction they produce seeds. The seed contains the embryo and stored food, which is used for the initial growth of the embryo during germination.
• The plant body is well differentiated into root, stem and leaves.
• They have well-developed conducting tissues for water and food.
• Depending on whether the seeds are enclosed in a fruit or not, they are divided into two groups: gymnosperms (naked seeds, e.g. Cycas, Pinus) and angiosperms (seeds inside fruits, e.g. mango, tamarind, maize).

1. Seed: a dicot seed has two cotyledons and splits into two equal halves; a monocot seed has a single cotyledon and cannot be split into equal halves.
2. Root: dicots have a well-developed primary root (tap root); monocots have fibrous roots.
3. Stem: dicot stems are usually strong and hard, e.g. banyan; monocot stems may be hollow (bamboo), false (banana) or disc-like (onion).
4. Leaf: dicot leaves have reticulate (net-like) venation; monocot leaves have parallel venation.
5. Flower: dicot flowers have parts in fours or fives or their multiples (tetramerous or pentamerous); monocot flowers have parts in threes or multiples of three (trimerous).
6. Examples: dicots — mustard, bean, groundnut, tamarind, mango; monocots — maize, wheat, rice, onion, banana.

• Spirogyra is a green alga of the division Thallophyta. It is found in freshwater ponds, tanks and slow streams as bright green, slimy threads.
• Its body is an unbranched filament made of many cylindrical cells joined end to end.
• Each cell has a cell wall and one or more ribbon-like chloroplasts arranged spirally inside it. This spiral arrangement gives the plant its name.
• Small round bodies called pyrenoids lie along the chloroplast; they store starch.
• A single nucleus lies in the centre of the cell, held by fine cytoplasmic strands across a large vacuole.
• Because it contains chlorophyll, Spirogyra makes its own food by photosynthesis; it is autotrophic.

• They grow in moist, shady places — on damp soil, old walls, bricks and rocks, especially in the rainy season.
• They need water for reproduction, so they are called the ‘amphibians’ of the plant kingdom.
• The plant body is thalloid, multicellular and autotrophic.
• The body is flat or ribbon-like and has no true roots, stem and leaves. Instead, it has stem-like and leaf-like parts, and root-like rhizoids that fix it to the ground.
• They have no special tissues for conduction of water and food.
• They reproduce by spore formation; the spores are formed in a capsule.
• Examples: moss (Funaria), Marchantia, Anthoceros, Riccia.

Marchantia is a bryophyte that grows as a flat, green, ribbon-like body called the thallus, lying close to damp soil or rock. The thallus forks into two lobes and acts as the leaf-like part. Fine, hair-like rhizoids on its lower surface fix it to the ground and absorb water. Small cup-like structures on the upper surface (gemma cups) help in vegetative reproduction. Upright stalks with umbrella-like heads carry the capsules in which spores are formed.

Funaria is a common moss that forms a soft green carpet on walls and rocks in the rainy season. The small plant has an upright stem-like axis with many small, green leaf-like parts arranged around it, and rhizoids at the base instead of true roots. A long, thin stalk grows from the tip and carries a capsule in which spores are formed. It has no tissues for conduction of water and food.

A fern is a pteridophyte. It has true roots, an underground stem called the rhizome, and large compound leaves (fronds) divided into many leaflets. Young leaves are coiled at the tip and unroll as they grow. It has well-developed conducting tissues. The fern does not bear flowers, fruits or seeds; brown dots called sori on the underside of the leaflets contain sporangia that produce spores.

See the labelled figure and description in answer 3(d) above. Spirogyra is a freshwater green alga (Thallophyta) with an unbranched filament of cylindrical cells. Each cell has a cell wall, spiral ribbon-shaped chloroplasts with pyrenoids, and a central nucleus.

Here is a model description of one monocot and one dicot plant that are easy to find. Describe the plants you actually collect in the same way.

Plants are classified step by step, using the following criteria in this order:

1. Presence or absence of organs (differentiation of the plant body): whether the body is divided into root, stem and leaves. Thallophytes have no such parts; bryophytes have only root-like, stem-like and leaf-like parts; pteridophytes and seed plants have true roots, stems and leaves. This shows the level of development of the plant.
2. Presence or absence of conducting tissues: whether there are separate tissues for conduction of water and food. Thallophytes and bryophytes have none, so they stay small and depend on moist places. Pteridophytes and seed plants have them, so they can grow large and live on land.
3. Presence or absence of flowers, fruits and seeds: plants that do not bear these, and whose reproductive organs are hidden, are cryptogams (Thallophyta, Bryophyta, Pteridophyta). Plants that bear seeds are phanerogams. This separates plants that reproduce by spores from those that reproduce by seeds.
4. Seeds enclosed in a fruit or not: phanerogams with naked seeds are gymnosperms (Cycas, Pinus); those whose seeds form inside a fruit are angiosperms (mango, tamarind).
5. Number of cotyledons in the seed: angiosperms with two cotyledons are dicotyledons (mustard, bean); those with one are monocotyledons (maize, wheat).

Using these criteria in order, from general to specific features, arranges the great diversity of plants into groups of increasingly similar plants. This makes plants easier to study and identify.

• (a) Talk on plant classification: in 5 to 7 minutes, cover the basis of classification (the five criteria in Q6), the two subkingdoms, one example with a special feature from each division, and why plants matter to all other living things.
• (b) Album of monocot and dicot seeds: soak the seeds for 8–10 hours and try to split them. Seeds that split into two halves (bean, groundnut, tamarind, mango, gram) go on the dicot page; seeds that do not (maize, wheat, rice, jowar, bajra) go on the monocot page. Label each with its name.
• (c) Photographs: Thallophyta — Spirogyra, Ulothrix, Ulva, Chara, Sargassum; Bryophyta — Funaria, Marchantia, Riccia, Anthoceros, Polytrichum; Pteridophyta — Nephrolepis, Adiantum, Pteris, Marsilea, Equisetum. Write two or three lines under each on where it grows and its body features.