Pharmacognosy - Leaves Overview

Pharmacognosy - Leaves

• Leaves are lateral outgrowths from stems, typically flattened
• Leaves consist of three main parts: leaf base, blade (lamina), and stalk (petiole)
• Leaf blade's lamina is typically expanded and widest at its broadest portion
• Different types of leaves exist (e.g., petiolate, sessile, stipulate, ex-stipulate) depending on the presence/absence of petiole and stipules.
• Cotyledons (seed leaves) store food reserves (proteins)
• Prophylls are simpler in form and structure than regular green leaves
• Foliage leaves carry out normal leaf functions
• Scale leaves are thin, membranous, and lack chlorophyll, often found on subterranean stems or some aerial stems.
• Bracts are leaves with flowers or groups of flowers in their axils
• Modified leaves can be modified into different structures for specific functions, such as tendrils (e.g., peas), spines (e.g., orange), traps for insects (e.g., sundews), or water storage (e.g., some succulents).

Phyllotaxis

• Phyllotaxis is the arrangement of leaves on a stem
• Alternate (Spiral): leaves are inserted singly at nodes at regular intervals
• Opposite: a pair of leaves is developed at each node, opposite to each other
• Opposite decussate: opposite leaves are inserted at right angles to the pair above and below
• Whorled: three or more leaves occur at a single node

Leaf Base

• Stipules are lateral outgrowths from the leaf base
• Stipulate: leaves with stipules
• Exstipulate: leaves without stipules

Lamina (Leaf Blade)

• Simple leaf: continuous, undivided surface; without lobes or divisions
• Lobed leaf: lamina cut divided into lobes connected by undivided portions
• Pinnately lobed: incisions directed towards the midrib
• Palmately lobed: incisions directed towards the petiole's top
• Compound leaf: lamina divided into separate leaflets.
• Types of compound leaves: Binate (2 leaflets), Ternate (3 leaflets), Pinnate, and Palmate.

Shape of Lamina

• Filiform: thread-like
• Acicular: tube-like (needle-shaped)
• Tubular: tube-like (e.g., onion)
• Linear: flat, edges generally parallel near the midline
• Ovate: egg-shaped, widest portion near the base
• Lanceolate: narrow, gradually tapering to the tip
• Obvate: inverted ovate

Apex of Lamina

• Acute: sharply pointed at the tip
• Acuminate: tapering to a sharp point
• Obtuse: rounded or blunt tip
• Mucronate: abruptly pointed tip
• Recurved: bent or curved backward
• Emarginate: notched at the tip

Margin of Lamina

• Entire: smooth margin
• Crenate: rounded teeth
• Denate: straight teeth, pointed outwards
• Serrate: saw-toothed (teeth pointed towards apex) - Ciliate: fringed with hairs

Base of Lamina

• Symmetric: equal on both sides
• Asymmetric: unequal on both sides
• Decurrent: continuous downwards like wings along the base.
• Cordate : heart-shaped

Venation

• Parallel: Veins run parallel to the margin
• Pinnate: single main vein with smaller veins branching off
• Palmate: several main veins departing from the petiole at the apex

Leaf Surface

• Glabrous: smooth, free from hairs
• Pubescent: hairy
• Punctate: dotted with oil glands

Senna Leaf

• Senna leaflets are the dried leaflets of Cassia senna
• Senna is used as a laxative
• Senna leaves are collected and prepared for use and export.

Belladonna Leaf

• Belladonna consists of the dried leaves of Atropa belladonna
• Belladonna is used for spastic conditions of stomach and intestine

Digitalis Leaf

• Digitalis consists of the dried leaves of Digitalis purpurea
• Digitalis is used in cases of cardiac failure.

Stramonium Leaf

• Stramonium leaf consists of the dried leaves of Datura stramonium and its varieties
• Stramonium leaf is used to control motion sickness

Buchu Leaf

• Buchu is the dried leaves of Agathosma betulina
• Buchu is traditionally used as a urinary antiseptic.

Boldo Leaf

• Boldo is the dried leaves of Peumus boldus Molina
• Boldo is used for gallstones, liver, stomach, and digestive issues.

Jaborandi Leaf

• Jaborandi is the dried leaflets of Pilocarpus microphyllus
• Jaborandi is used ophthalmically in glaucoma treatments.

Henna Leaf

• Henna consists of the dried leaves of Lawsonia inermis
• Henna is used as a hair dye.

Bearberry Leaf

• Bearberry is the dried leaves of Arctostaphylos uva ursi
• Bearberry is used for urinary infections

Green and Black Tea

• Tea consists of the prepared leaves of Thea sinensis
• Used for antioxidant activities and protecting against cancer and tooth decay