Morphology of Flowering Plants Class 11 Notes

Root System

The root system is the underground part of the plant that anchors it, absorbs water and minerals, and stores food. In most dicots the primary root grows deep and branches — this is the tap root system. In most monocots the primary root is short-lived and replaced by a cluster of thin roots — the fibrous root system. Some plants like grass and banyan develop roots from nodes of the stem or even from leaves — these are adventitious roots.

Modifications of the Root

• Storage roots: swollen with food — carrot (conical), turnip (napiform), sweet potato (tuberous).
• Support roots (prop roots): arise from lower stem branches, grow down into soil — e.g. banyan.
• Respiration roots (pneumatophores): vertical roots growing upward in mangroves (Rhizophora) with pores (lenticels) for gas exchange.
• Assimilatory roots: green, perform photosynthesis — e.g. Tinospora.
• Sucking / haustorial roots: penetrate host tissue to absorb nutrients — e.g. Cuscuta (parasitic plant).

Stem

The stem is the aerial part that bears leaves, flowers and fruits. It has nodes (points of leaf attachment) and internodes (regions between nodes). Stems can be herbaceous (soft, green) or woody. Underground stems like potato and ginger store food; aerial stems may bear thorns (cactus) or tendrils (grapevine) for support.

Modifications of the Stem

• Runners (stolons): horizontal stems that creep along the ground and root at nodes — e.g. grass, strawberry.
• Tubers: swollen underground stem tips for food storage — e.g. potato. Each eye is a bud.
• Tendrils: thin coiling structures for climbing — e.g. grapevine, pea.
• Bulb: short stem with fleshy leaves — e.g. onion, garlic.
• Corm: short, swollen underground stem — e.g. Colocasia, saffron.
• Phylloclade: flattened, leaf-like photosynthetic stem — e.g. Opuntia.

Leaf

A leaf is a flat, green, photosynthetic organ that arises from a node. It has a leaf base (petiole in stalked leaves, sheath in grasses), a lamina (blade) and veins. Leaves may be simple (single lamina) or compound (lamina divided into leaflets — pinnate like neem, palmate like silk cotton).

Venation and Phyllotaxy

• Reticulate venation: veins form a network — typical of dicots (mango, peepal).
• Parallel venation: veins run parallel — typical of monocots (grass, maize).
• Alternate phyllotaxy: one leaf per node — mustard, sunflower.
• Opposite: two leaves per node on opposite sides — guava, Calotropis.
• Whorled: more than two leaves at a node — Alstonia.

Modifications of the Leaf

• Tendrils: leaf or leaflet modified for climbing — e.g. pea.
• Spines: defence — e.g. cactus (Opuntia).
• Pitcher: insectivorous — e.g. Nepenthes (pitcher plant).
• Fleshy leaves for storage — e.g. onion, garlic.

The Flower

A flower is the reproductive shoot. It has four whorls on the thalamus: calyx (sepals — green, protective), corolla (petals — coloured to attract pollinators), androecium (stamens — male, each with anther and filament) and gynoecium (carpels — female, each with stigma, style and ovary). A flower is complete when all four whorls are present, incomplete when any whorl is missing.

Symmetry and Key Terms

• Actinomorphic (radial symmetry): can be divided into equal halves by any plane passing through the centre — e.g. mustard, rose.
• Zygomorphic (bilateral symmetry): can be divided into equal halves by only one plane — e.g. pea, gulmohar.
• Asymmetric: cannot be divided into two equal halves — e.g. cyclamen.
• Cohesion: fusion of similar parts (e.g. stamens united in tubiflorous condition).
• Adhesion: fusion of dissimilar parts (e.g. stamens fused to petals — epipetalous).
• Epiphyllous: stamens attached to petals.

Position of Ovary

• Hypogynous: ovary superior — other whorls below it — e.g. mustard, china rose.
• Perigynous: ovary half-inferior — thalamus forms a cup around it — e.g. peach, rose.
• Epigynous: ovary inferior — other whorls above it — e.g. guava, cucumber, sunflower.

Fruit and Seed

After fertilisation the ovary develops into the fruit. A true fruit develops solely from the ovary — e.g. mango, pea. A false fruit (pome) develops partly from the thalamus — e.g. apple, strawberry. A parthenocarpic fruit develops without fertilisation — e.g. banana, seedless grape.

• Fruit parts: pericarp (fruit wall from ovary wall) which may be fleshy or dry, and seeds.
• Dicot seed: two cotyledons store food; embryo has radicle, plumule and hypocotyl. Endosperm may be present (albuminous — castor) or consumed (non-albuminous — pea).
• Monocot seed: one cotyledon (scutellum in grasses); endosperm present; embryo has coleoptile (shoot tip cover) and coleorhiza (root tip cover). Seed coat is fused with fruit wall (pericarp) in grains.

Major Families — Fabaceae, Solanaceae, Liliaceae

Solved Examples

Example: The root system of wheat is fibrous while that of mustard is tap root. Why does this difference arise?

Solution: Wheat is a monocot — its primary root is short-lived and replaced by many adventitious roots arising from the stem base, giving a fibrous root system. Mustard is a dicot — its radicle grows continuously into a prominent primary root that branches laterally, forming a tap root system. The embryonic type (monocot vs dicot) determines the root architecture.

Example: A flower is described as epigynous with axile placentation. Identify the possible fruit and name one real example.

Solution: In an epigynous flower the ovary is inferior; after fertilisation the fruit wall (pericarp) develops below the attachment of the other floral parts, often with the floral remnants visible on top. Axile placentation means the ovary has multiple chambers with ovules on a central axis. A common example is the tomato (Solanaceae) — it is a berry with many seeds arranged around the central axis.