MORPHOLOGY OF FLOWERING PLANTS Types of Plant Organs

MORPHOLOGY OF FLOWERING PLANTS

Types of Plant Organs • Vegetative organs: – Roots – Leaves – Stems • Reproductive organs: – Flowers – Fruit

Plant Body Systems • The plant body is organized into a root system and a shoot system: – Root system is generally below ground. – Shoot system consists of vertical stems, leaves, flowers, & fruit that contain seeds.

Roots • Absorb water & minerals • Anchor the plant • Storage (Some Roots)

Types of Roots Taproot Prop Root Fibrous Root

TAP ROOT • Seen in dicots. • The direct elongation of the radicle leads to the formation of primary root which grows inside the soil. • It bears lateral roots of several orders that are referred to as secondary, tertiary, etc. roots. • The primary roots and its branches constitute the tap root system

FIBROUS ROOT • In monocotyledonous plants, the primary root is short lived and is replaced by a large number of roots. • These roots originate from the base of the stem and constitute the fibrous root system

Tap roots Fibrous roots

ADVENTITIOUS ROOTS • In some plants, like grass, Monstera and the banyan tree, roots arise from parts of the plant other than the radicle and are called adventitious roots.

Regions of the Root • The root is covered at the apex by a thimble-like structure called the root cap. It protects the tender apex of the root as it makes its way through the soil. • A few millimetres above the root cap is the region of meristematic activity. The cells of this region are very small, thin-walled and with dense protoplasm. They divide repeatedly. • The cells proximal to this region undergo rapid elongation and enlargement and are responsible for the growth of the root in length. This region is called the region of elongation. The cells of the elongation zone gradually differentiate and mature. • The zone proximal to region of elongation, is called the region of maturation. From this region some of the epidermal cells form very fine and delicate, thread-like structures called root hairs. These root hairs absorb water and minerals from the soil.

REGIONS OF THE ROOT

MODIFICATIONS OF ROOT 1. STORAGE ROOTS: i) Adventitious roots become tuberous in sweet potato. ii)Tap root modified for storage become swollen with food material and depending on the shape of the storage roots , they are described as follows: a)CONICAL –Eg. Carrot b)FUSIFORM: Eg. Raddish c)NAPIFORM- Eg. Beetroot, turnip D)TUBROUUS-Eg. Mirabilis

Fleshy Tap Roots • Carrots, beets, and radishes are examples of plants forming fleshy tap roots. Carrots

Tuberous Roots • Sweet potato is an example of a tuberous root. A sweet potato is a tuberous root

Tuberous Roots • Dahlias are perennial bedding plants that form tuberous roots. Dahlia

2. STILT ROOT • These are adventitious roots which arise in cluster from the basal nodes just above the ground Eg. Maize, sugar cane, pandanus. Pandanus

Prop roots such as these inspired flying buttresses. Pandanus utilis - screw pine

Prop Roots • Massive pillar like outgrowths of aerial branches , which grow downwards and become large and woody. • Banyan

Pneumatophore • Rhizophora plants have pneumatophores. • They are negatively geotrophic. Grow upwards • Does respiration Mangrove plants

Stems

Stems • Stems are the part of the plant from which the shoots and buds arise. • Arises from plumule. • Stems (and leaves) are the most conspicuous and diverse organs of plants: – Trunk of a tree – Stem of a flower

Structure of Stems • A stem is a collection of integrated tissues arranged as nodes and internodes. – Nodes: regions where leaves attach to stems – Internodes: parts of stems between nodes

Functions of Stems • Stems perform important functions: – Support leaves, flowers, & fruits – Produce carbohydrates – Store materials – Transport water and minerals – Protection/Defense – Anchorage

DIVERSE FORMS OF STEMS • UNDERGROUND STEMS – RHIZOME – BULB – CORM – TUBER • SUB-AERIAL STEMS – RUNNER, SUCKER, STOLON, OFFSET • AERIAL STEM – TENDRIL, THORN, PHYLLOCADE, CLADODE.

Tubers • A tuber is an underground stem that stores food. • potato is a tuber because it has nodes (eyes) which produce new shoots. Potato is a tuber

Corms • A corm is a swollen, vertical stem with a papery covering. • Gladiolus and Crocus are examples of plants that form corms. Crocus corms

CORMS

Bulbs • A shortened underground bud in which fleshy storage leaves are attached to a short stem. • Bulbs are rounded and are covered with paper-like bud scales, which are actually modified leaves! • Examples: – Onions – Garlic – Tulips – Daffodils

Rhizomes • Rhizomes are: – underground stems. – horizontally-growing. – produce shoots and adventitious roots. Iris rhizome

Runners • Horizontal, above ground stems that grow along the ground’s surface and are characterized by long internodes. • Buds develop along the stolon and give rise to new plants that root in the ground. • Examples: – Strawberry – Nut grass

SUCKER • It is a branch arising from the basal ans underground part of main stem • Grows horizontally for a short distance under the soil and emerges obliquely above the ground and bears a leafy shoot.

STOLON • It is a slender , lateral branch that arises from the base of the main stem. • Aerial branch arches downwards to touch the ground. • Eg. Jasmine.

OFFSET • A lateral branch with short internodes and each node bearing a rosette of leaves and a tuft of roots is found. • Eg. in aquatic plants like Pistia and Eichhornia

Tendrils • Stem tendrils which develop from axillary buds, are slender and spirally coiled and help plants to climb. • Examples: – gourds (cucumber, pumpkins, watermelon) – grapevines.

Thorns • Modified stems that protect plants from grazing animals. • Example Citrus, Bougainvillea

Phylloclade • Phylloclade are: – Above ground stems. – Grow horizontally or vertically. – Do not have leaves – Leaves are modified to form spine – They store water and are succulent. – Are green and perform photosynthesis. – Cactus, opuntia.

Leaves A plant’s “solar panels” …

Leaves • The leaf is a lateral, generally flattened structure borne on the stem.

• It develops at the node and bears a bud in its axil. The axillary bud later develops into a branch. • Leaves originate from shoot apical meristems and are arranged in an acropetal order.

Basic Leaf Structure • Most leaves are flat with a transparent epidermis. • Most leaves are composed of two parts: – Blade: the broad, flat portion of the leaf • Vein • Midrib – Petiole: the stalk that attaches the blade to the stem. • Stipule outgrowths) (leaf

Leaves Vary Greatly in Form • Leaves are the most variable plant organ—so much that botanists developed terminology to describe their shapes, margins, vein patterns, and attachment methods. • Leaves may be round, needlelike, scale-like, cylindrical, heart-shaped, fan-shaped, or thin and narrow. • Vary in size from >20 meters (Raffia palm) to microscopic (duckweed).

VENATION • The arrangement of veins and the veinlets in the lamina of leaf is termed as venation. • When the veinlets form a network, the venation is termed as reticulate. • When the veins run parallel to each other within a lamina, the venation is termed as parallel. • Leaves of dicotyledonous plants generally possess reticulate venation, while parallel venation is the characteristic of most monocotyledons

Reticulate parallel.

VENATION

TYPES OF LEAVES • Leaves may be: – Simple – Compound • Pinnately compound (leaflets arise as continuation of petiole) • Palmately compound (leaflets arise from a common point on the petiole)

PHYLLOTAXY • Leaf Arrangement on stem. • Leaves are arranged on a stem in three possible ways: – Alternate: one leaf at each node – Opposite: two leaves at each node – Whorled: > 3 leaves at each node

Leaf Lobing • Leaf lobes can be: – Pinnate: lobes arising along the length of midvein – Palmate: lobes arising from one main point at the base of the leaf

Leaf Shapes

Leaf Margins

MODIFICATIONS OF LEAVES • • • Tendrils Stipules Spines Bud scales Window leaves Bracts Storage leaves Flowerpot leaves Insect-trapping leaves Propagating Leaves Cotyledons

Tendrils • Modified leaves that provide support – Examples: • Garden pea

Leaf Tendrils

Stipules • Small, leaf-like structures at the base of the petiole • May protect plant (black locust) or support it (greenbriars)

Spines • Leaves modified for protection.

Leaf Spines

Bracts • Floral leaves that form at the base of a flower or flower stalk. • Protect the developing flowers.

Storage leaves • Fleshy, concentric leaves modified to store food

Flowerpot Leaves • Urn-like pouches that catch falling water and debris. • Many epiphytes (orchids) grow roots among these leaves to absorb water and nutrients from them.

Insect trapping Leaves • Insect eating leaves trap insects in various ways • Examples: – – Venus flytrap Sundew plant Pitcher plant Bladderwort

Venus flytrap • Plants have leaves that bend in the middle, with each half looking like half a trap. • When an insect trips 2 of the 3 trigger hairs the leaf snaps shut and enzymes digest the insect. – Falling water and dirt do not trip the trigger hairs!

Sundew n Leaves have mucilage- coated sticky hairs that attract and trap insects. n Once insect is attached to the hairs, the leaf folds around it; enzymes digest the insect. n After digestion leaf resumes its normal shape and secretes new mucilage.

Pitcher plant • Leaves shaped like a pitcher or vase that collects water. • Glands around their tops secrete nectar to attract insects, which often fall into the trap and drown. – Some have bristles that point downward preventing escape. – In Malaysia some tree frogs lay their eggs in the “traps” ensuring water and food for offspring; these eggs produce enzymes that protect them!

Pitchers

Bladderwort • An aquatic plant that produces tiny “bladders” with a trap door. • The bladders (< ½ cm) open their doors when an aquatic insect brushes against one of the trigger hairs and water rushes in with the insect; the door closes and enzymes digest it.

Phyllode • They are specialized for reducing the rate of transpiration. • In these structure the rachis look like leaf or petiole modifies to form leaf like structure while leaf lamina is highly reduced

Phyllode

The Economic Importance of Leaves • • Food (cabbage, lettuce) Spices (peppermint) Drinks (agave for tequila) Dyes (henna) Fibers (palm leaves) Drugs (tobacco) Lotions (aloe)