Leaf Morphology: Margins, Venation & Surfaces

Margin of Leaves

• Margins can be described as entire, dentate, or serrate.
• Entire margins are quite smooth.
• Dentate margins have teeth pointed straight outwards.
• Serrate margins have sharp teeth directed towards the apex.

Venation

• The lamina contains vascular strands that form the veins, projecting usually on the lower side.
• A midrib is the strongly developed vein in the middle of the lamina
• Venation describes the disposition and arrangement of veins
• The venation of the lamina can be described as parallel or reticulate.
• Parallel venation occurs when veins of equal size run side by side parallel to each other.
• Reticulate venation occurs when lateral veins branch off into smaller veins and veinlets, forming a network.

Surface of Leaves

• The upper surface of the lamina is usually a darker green, while the lower is paler.
• A leaf surface can be smooth, wrinkled, or punctate.
• Punctate: dotted with projection formed by oil glands
• Glabrous: free from hairs
• Spinose: set with spines
• Hairy: containing hairs

Structure of the Lamina

• A leaf typically consists of the following tissues: epidermis, mesophyll, and a vascular system.
• Epidermis: covers the upper and lower surfaces
• Mesophyll: an interior chlorenchyma, including palisade and spongy mesophyll

Leaves Containing Alkaloids

• Types of leaves that contain Alkaloids are: Stramonium, Egyptian henbane, Belladonna, Jaborandi, Tea, and Coca leaves.

Stramonium Leaf

• Stramonium Leaf is also known as Thorn Apple.
• The active part of the plant is the dried leaves and flowering tops of Datura stramonium and Datura tatula.
• Stramonium plants are part of the Solanaceae family.
• Stramonium plants grow in Europe, Asia, and America.
• Stramonium Leaf macromorphology: greyish-green color, ovate or triangular ovate shape, dentate margin, asymmetric base, acuminate apex, not strong odour, and bitter taste

Stramonium Powder

• Stramonium powder is grayish-green to brownish-green, with a characteristic odour and bitter taste
• Stramonium powder contains fragments of upper and lower epidermises having anisocytic stomata and carrying hairs
• Also contains crystal layer fragments, xylem vessels and veinlets, spongy parenchyma, cluster crystals of calcium oxide
• Stramonium powder also contains fragments of palisade cells containing chloroplasts, scattered clusters and prisms of CaOx crystals, xylem vessels with spiral thickening

Stramonium Active Constituents

• The Stramonium plant includes Atropine, Hyoscyamine, and Hyoscine

Therapeutic Uses of Stramonium

• Atropine is used in ophthalmology to dilate the pupil of the eye and therefore used for examination of eye as eye drops.
• Atropine relaxes the intestinal and bronchial smooth muscles and is therefore used as an antispasmodic
• Atropine is used in preanesthetic medication to stop or inhibit body secretions, working as a parasympatholytic agent
• Hyoscine has sedative action and is used in the control of motion sickness
• Hyoscyamine decreases motion of the stomach and intestines, as well as secretion of stomach fluids including acid
• Hyoscyamine is used in the treatment of bladder spasms, peptic ulcer disease, colic, irritable bowel syndrome, cystitis, and pancreatitis

General Chemical Test for Alkaloids

• Mayer's Test: Shake the powder with dilute HCl -> filter, then add a drop of Mayer's reagent to yield a creamy white ppt.
• Mayer's reagent is Potassium mercuric iodide and yields a creamy white colored ppt

Specific Chemical Test for Solanaceous Alkaloids

• Vitali-Morin Test: Evaporate 1ml of alkaloidal solution on a water bath until dryness.
• Add 2 drops of concentrated HNO3 and evaporate until dryness, then cool and add 1 drop of freshly prepared alcoholic KOH (10%) to yield a bright purple colour.

Egyptian Henbane Leaf

• Egyptian henbane leaves consists of dried leaves and flowering tops of Hyoscyamus muticus
• Egyptian henbane plants are part of the Solanaceae family, originating from Egypt
• As Datura leaves show the active constituents and uses
• Macromorphology: pale-green to yellowish-green color, oval shape, entire margin or with 2-5 teeth on each side, symmetric base, acuminate apex, narcotic odour, and bitter taste

Egyptian Henbane Powder

• Egyptian Henbane powder is pale to yellowish-green with little odour and a slightly bitter taste.
• Contains fragments of upper and lower epidermises having anisocytic stomata and carrying hairs
• Fragments of palisade cells containing chloroplast
• Fragments of xylem vessels with spiral thickening
• Parenchyma cells containing prisms and twins crystals of ca.ox

Comparison of Hyoscymus Species

• Hyoscymus niger: Indian or European Henbane
• Hyoscyamus muticus is a non-official drug, the leaf is isobilateral, has branched glandular hairs, no solanaceous hairs, and no collenchyma.
• Hyoscyamus niger is an official drug, the leaf is dorsiventeral, has no branched glandular hairs, has covered solanaceous hairs with warty cuticle, and contains upper and lower collenchyma.
• Hyoscyamus muticus - Epidermal cells covered with a thick striated cuticle and has alkaloidal composition of (0.8 - 1.7 %) with mainly Hyoscymine and little Atropine and Hyoscine
• Hyoscyamus niger - Epidermal cells are covered with smooth cuticle and has alkaloidal composition of (0.04 – 0.05%) with mainly Hyoscymine and little Atropine and Hyoscine

Explore leaf morphology: margins (entire, dentate, serrate), venation (parallel, reticulate), and surface textures (smooth, wrinkled, punctate, glabrous). Discover how these features define and differentiate various plant leaves.