Plant Leaf Morphology & Function

• The leaf is a lateral outgrowth (appendage) showing limited growth, differing in organization and structure from the stem, usually flattened with an axil bud or branch, consisting of primary tissues without nodes or internodes.

Leaf Functions

• Leaves facilitate the assimilation of glucose and starch from water and carbon dioxide through photosynthesis, fueled by sunlight.

Types of Leaves

• Cotyledons (seed leaves): They store food for the embryo.
• Foliage leaves: Ordinary green ones responsible for photosynthesis.
• Floral leaves: Reproductive parts of a flower (sepals, petals, stamens, carpels).
• Bract leaves: These have a flower in their axils and an axillary bud that modifies into a flower.
• Scale leaves: They are on subterranean stems, are thin, membranous, lack chlorophyll, and protect inner parts.
• Modified leaves: These are specialized for functions like spines for protection in orange plants and tendrils for climbing for grapes.

Morphological Structure of a Dicot Leaf

• Leaves show shape variations for identification and consist of a lamina/blade and a petiole.
• Some leaves have stipules, small leaf-like outgrowths at the base
• Petiole (optional): It attaches the blade to the stem.
• Lamina/Blade: It is broad, flat, and collects light for photosynthesis.
• Veins: They contain vascular tissue.
• Axil: It is the leaf's attachment point, the intersection of petiole and stem, and sometimes has an axillary bud.
• Stipules (optional): They are outgrowths at the leaf base.

Leaf Forms

• Simple leaves: Blades are undivided.
• Entire (single) blade: The leaf is not divided
• Lobed or deeply lobed:
• Pinnately lobed: Lobes arranged on the sides of a central axis.
• Palmately lobed: Lobes spread radially from a central point.
• Compound leaves: Each blade divides into leaflets.
• Pinnate leaflets: Leaflets arise along the sides of the rachis, which is the extension of the petiole.
• Paripinnate: Leaflets are even in number.
• Imparipinnate: Leaflets are odd in number.
• Palmate: The blade divides from the top of the petiole into 5+ leaflets.

Venation Types

• Parallel venation: Characteristic in monocotyledons. Veins run parallel to each other.
• Multicostate venation: There are multiple main veins/ribs radiating from the leaf's base.
• Unicostate venation: One main vein runs through the leaf center.
• Netted venation: Characteristic of dicotyledons.
• Pinnately netted: Veins branch/radiate from a central mid-vein.
• Palmately netted: Major veins radiate outwards from one point.

Leaf Arrangement on Stem (Phyllotaxis)

• Alternate: One leaf per node.
• Opposite: Nodes are opposite with 2 leaves per node.
• Opposite Decussate: Successive leaf pairs are at right angles, common in the mint family.
• Whorled: Three or more leaves arise from one node.

Leaf Histology

• Ordinary leaf consists of upper/lower epidermis, mesophyll, cortical tissues, and vascular system.
• Upper and lower epidermis: The lower surface has more stomata for gas exchange.
• Mesophyll: It lies between the two epidermal layers.
• Cortical tissues: They surround the vascular bundle within the mesophyll.
• Vascular system.
• Microscopic characteristics of leaves: Include stomata traits, trichomes (glandular/non-glandular hairs), and crystals such as calcium oxalate.

Senna (Alexandrian & Indian Senna)

• Origin: The dried leaflets of Cassia acutifolia (Alexandrian Senna) and Cassia angustifolia (Indian Senna) from the Leguminosae family.
• Active constituents: It is composed of anthraquinone glycosides (Sennosides A, B, C, D) that release Sennidins A, B, C, D upon hydrolysis, and also mucilage.
• Confirmatory Chemical Tests: Borntrager's test indicates free anthraquinones if a chloroformic extract turns rose (pink) to intense red with NH4OH in the aqueous layer.
• Another test is Modified borntrager's: A chloroformic extract indicates combined anthraquinones if it turns a rose (pink) to intense red with NH4OH in the aqueous layer.
• Medicinal uses include the presence of anthraquinone glycosides.
• Senna is used as a laxative and powerful cathartic for constipation.
• Precautions: Senna weakens large bowel muscles if taken for over 10 days.
• Side effects: Due to anthraquinone glycosides, it can cause nausea and gripping/colic and is often mixed with aromatic herbs to counter the effects, such as mint, anise, cardamom, clove, and antispasmodics.
• Contraindications: It should not be used during pregnancy as muscle contractions may cause abortion and plus woman breastfeeding
• Morphology: The petiole of senna is petiolate.
• The lamina (leaf blade):
• Shape: obovate, lanceolate.
• Margin: entire.
• Form: compound, pinnate, paripinnate.
• Venation: reticulate (netted) and pinnately reticulate.
• Phyllotaxis: alternate.
• Key Elements: The KOH mount shows palisade cells (leaf organ).
• Longitudinal collenchyma is observed, as well as upper/lower epidermal cells with paracytic stomata.
• The species has a warty hair non-glandular, unicellular cuticle and crystals with Ca-Oxalate.

Digitalis (Foxglove)

• Origin: The dried leaves of Digitalis purpurea and Digitalis lanata, from Scrophulariaceae.
• Active constituents include cardiac glycosides (Digoxin, Digitoxin, Lanatoside A/C) and saponin glycosides.
• Confirmatory Tests: Baljet test: An alcoholic extract yields orange-yellow when reacted with picric acid and NaOH.
• Keller–Killiani test indicates deoxy sugars if an acidic extract shows a reddish-brown ring with FeCl3 and H2SO4, turning the upper layer bluish-green.
• Froth test (for Saponin glycosides): Powdered drug shaken with water gives persistent froth for 5 minutes.
• Medicinal uses: Digitalis has cardiac tonic actions (strengthens heartbeat, increases contraction force), enabling a stronger, slower, regular rhythm with less oxygen requirement, due to cardiac glycosides.
• Precautions: Digitalis cardiac glycosides are slowly excreted, accumulate, and can be fatal with long-term use.
• Morphology:
• A. Digitalis petiole is petiolate.
• B. The lamina (leaf Blade):
• Apex: acute
• Shape: lanceolate and decurrent
• Margin: entire, ciliated
• Form: simple
• Venation: reticulate anastomosing near the margin.
• Apex: exstipulate.
• C. Phyllotaxis: alternate.
• Key Elements: The KOH mount shows fragments of epidermal cells with beaded walls and anomocytic stomata with striated cuticle.
• Types of hairs: glandular and non-glandular but doesn't have calcium oxalate.

Tea

• Origin: The prepared leaves and leaf bud of Thea sinensis L. (Camellia thea Link.) and Family Theaceae.
• Part Used: The two adjacent young leaves with stem.
• Geographical Origin: India, Serilanka, China and Japanese.
• Types Based on Processing: Green tea (rapid drying, no fermentation) and black tea (slow drying, complete oxidation/fermentation).
• Active constituents for both include caffeine-phlobatannins complexes, tannins, traces of alkaloids, volatile oil, saponin glycosides, and flavonoids. Green tea contains more flavonoids, acting as an antioxidant.
• Green tea stops or destroys the enzyme. Black tea has complete oxidation by oxidase enzyme.
• Confirmatory Tests: Murexide test tests for caffeine where a product will form a crimson red when heat and ammonia vapors are passed over it.
• Ferric chloride helps to test for tannins and KOH test is for flavonoids glycosides.
• Froth test tests for Saponin glycosides.
• Medicinal Uses: Based on caffeine, tea acts as a CNS stimulant, diuretic, and weak muscle relaxant.
• Based on tannins, it functions as an antidiarrheal.
• Precautions:High doses of tea may cause gastritis, anemia, constipation, habituation, or increased heart rate.

Herb in Botany

• A non-woody plant having a non-permanent stem that dies at the end of the second year with no hard stem.
• Herb in Pharmacognosy:
• A drug that is comprised of a tender section of the plant, usually the stem, flower and fruit.

The Stem

• Definition: Plant axis bearing leaves and flowers.
• The stem is either aerial or subterranean.
• Functions: It supports/displays leaves, flowers, and fruits. It moves water/minerals and manufactures food, while subterranean scales protect without chlorophyll.
• Kinds of stems: Its shape can be cylindrical, angular (triangular, quadrangular, pentagonal), ribbed, winged, flattened or twisted, and its can be herbaceous, succulent, woody, creeping, climbing, or twining.
• Anatomy: Ground tissue composed of the pith, cortex, and medullary rays. The vascular bundles are arranged in a ring and may be connected by the interfascicular cambium.

Herbs vs Shrubs vs Trees

• Herbs are short with non-woody soft stems, do not have branches, annuals, biennials, or perennials that add flavor to food.

Mentha (Peppermint)

• Origin: The dried leaves and flowering tops of Mentha piperita (Labiatae family).
• Active Constituents: It is composed of volatile oils (menthol and menthone), flavonoids, phenolic acids, tannins, and triterpenes.
• Confirmatory Chemical Tests-
• Tests may be run for the presence of different compounds like Sudan III or Vanillin tests.
• Medicinal Uses: Used for gastrointestinal issues, increasing digestive flow, reducing gut muscle spasms, and relieving gases and spasms due to active compounds (volatile oils and flavonoids).
• Morphology: (Square shape, dark green leaves, light petioles).