Medicinal Plants Lect.7 Leaf Introduction PDF

MEDICINAL PLANTS 2024/2025 FALL SEMESTER  LECTURE 7 THE LEAF Dr. Amr Kotb The leaf (Folium)  The Leaf Definition:  The leaf is a lateral outgrowth on the stem from which it differs in structure and organization.  It possesses n...

MEDICINAL PLANTS 2024/2025 FALL SEMESTER  LECTURE 7 THE LEAF Dr. Amr Kotb The leaf (Folium)  The Leaf Definition:  The leaf is a lateral outgrowth on the stem from which it differs in structure and organization.  It possesses neither node nor internodes, having a bud in its axial and bears no buds. The complete leaf is composed of: 1- The leaf base. 2- Leaf stalk or petiole. 3- The blade or lamina. Types of Leaves: 1- Cotyledons (Seed leaves): for storage of reserve food material (protein). One in monocots, two in dicots and many in gymnosperms 2- Prophylls: (Fore - leaves) or first borne leaves. It differs from ordinary green leaves being simpler in form and structure. 3- Foliage leaves: The ordinary green leaves. Carry the normal leaf functions. Green due to chlorophyll. Leaf structure: (a)Petiole (c)Blade (b)Stipules (d)Base 4- Bracts: Leaves having a flower or group of flowers in their axils. 5- Scale leaves: They occur on all subterranean stems and on some aerial stems. They are thin membranous and devoid of chlorophyll. 6- Floral leaves: Including sepals and petals, stamens and carpels. (6) 7- Modified leaves: When the whole of the leaf or part of it may be modified into special structure to carry special functions. It may modify into (a) Tendrils e.g. Pea (b) Spines e.g. Cactus (c) Special traps for catching insects e.g. Drosera (d) Succulent for storage of water e.g. Zygophyllum.  Morphology of leaf 1. Texture: Brittle, coriaceous, papery, fleshy, membranous, leathery, etc... 2. Odour: may be aromatic or odourless. 3. Taste: May be bitter, sweet, mucilaginous, …… etc 4. Insertion: Position of leaf on the stem, may be: Cauline: Leaves spread on a long stem Radical: Leaves are crowded together about the top of the root, around a short stem, near ground or just above it. 5. Phyllotaxis: It is the disposition of the leaves on the stem. The different types of phyllotaxis are: 1) Alternate or spiral: When the leaves are inserted singly at the nodes (the most frequent type). 2) Opposite: When a pair of leaves is developed at each node and leaf is opposite to the other and it may be  Opposite superposed: The leaves are opposite and each pair is inserted parallel to the pairs immediately above and below.  Opposite decussate: The leaves are opposite and each pair is inserted at right angles to the pairs immediately above and below. 3) Whorled or verticillate: When three or more leaves occur at each node and arise in a circle around the stem.  Leaf structure Petiole Stipules Blade/Lamina Petiolate Stipulate Exstipulate Sessile Sheathing structure (decurrent base)  Structure of leaf 1- Leaf base: It is the attachment of the leaf to the stem and is slightly enlarged. Leaf bae may extend around the stem and form a sheathing structure (decurrent base). The leaf base develops lateral outgrowths called stipules which serve for the protection of the young auxiliary bud. When the stipules are present the leaf is described as stipulate, but when absent it is exstipulate. 2- Petiole or leaf stalk: It is the stalk that attaches the leaf blade to the stem and it carries the lamina away from the stem to perform its function. The petiole may show a localized swelling called pulvinus. It is responsible for the adjustement of the movement of the leaf towards the light. The leaf is described as sessile when the petiole is absent and petiolate when it is present.  Lamina (Leaf-blade): The lamina is the flat and widest part of the leaf. Based on the surface characters of the lamina there are two kinds of leaves, simple leaf and compound leaf. 1- Simple leaves: a) Simple entire leaf: When the lamina consists of a continuous undivided surface. b) Simple lobed leaf: When the lamina is cut up into a number of lobes connected with one another by an undivided portion. Incision of lobed leaves: If the incision is directed towards the midrib, the leaf is pinnately lobed. If incision is directed towards the top of the petiole, leaf is palmately lobed. 2- Compound leaves: The lamina is completely divided into a number of separate leaflets. The compound leaf consists of 2 or more leaflets either coming out from the top of the petiole or arranged on a central axis called Rachis. Types of compound leaves: Classified as pinnately compound leaves and palmately compound leaves. (A) Pinnately compound leaves: 1- In the even-pinnate leaflet arrangement, the arrangement of the leaflet is oppositely, and the rachis at the ends (termination point) is sprout with two leaflets, called as Paripinnate. 2- In the odd-pinnate leaflet arrangement, the leaflet arrangement is oppositely, but the rachis at the end is sprout with the single leaflet, called as Imparipinnate. Based on the pinnation arrangement, pinnately compound leaves are of three types, which are – Unippinate, Bipinnate, and Tripinnate. (B) Palmately compound leaves: Leaflets arise from the single point of the petiole Description of the lamina of simple leaf is: The important points required for lamina description are shape, margin, apex, base, venation and surface. I- Shape of the lamina (a)- When the lamina has the same width through out: 1- Filiform (thread like), as Fennel. 2- Acicular (needle shaped), as Pinus. 3- Tubular (flat long), as Onion. 4- Linear (flat long and very narrow), as Taxus. 5- Oblong (flat and wide) as Cassia. (b)- When the lamina has the widest portion near the base: 1- Lanceolate (narrow), as Buchu 2- Ovate (like egg), as Boldo 3- Cordate (heart shaped) 4- Reniform (kidney shaped), as Asarum (c) When the lamina has the widest portion near the apex: 1- Obcordate heart shape reversed, as Oxalis. 2- Obovate egg shape reversed, as Dog senna. 3- Spatulate flate like a spoon, as Uva-ursi. (d) When the lamina is symmetric or rounded: 1- Elliptical wide at the middle and tapering, as Pyrus. 2- Oval broadly elliptical, as Boldo. 3- Orbicular circular. II- Margin of the lamina: Leaf edges or margins, There are different types of leaf margins such as, Entire (quite smooth), Revolute (rolled back), Crenate (having numerous minute rounded lobes), Dentate (having teeth pointed straight outwards)., Serrate ( having sharp teeth directed towards the apex), Sinuate curved inwards and outwards, Ciliate has hairs, Spiny have spines, Bicrenate, Bidentate, and Biserrate,with sub teeth. Briefly, leaf margins can be divided into four major classifications you need to know and into which all others will fit: 1- Entire Leaf: The margin is even and smooth around the entire leaf edge. 2- Toothed or Serrated Leaf: The margin has a series of tooth-like pointed teeth around the entire leaf edge. 3- Lobed Leaf: The margin has an indention or indentions that go less than halfway to the leaf midrib or midline. 4- Parted Leaf: The margin has an indention or indentions that go more than halfway to the leaf midrib or midline. III- Apex of the lamina: The leaf tip, or apex, is used to help describe the leaf. There are many species with leaves that differ only slightly by shape but can be readily distinguished by their apices.e.g. 1- Acute: The two sides of the margin form an acute angle at the tip, e.g. Hyoscyamus. 2- Acuminate: The point is longer than in acute and the apex is more tapering, e.g. Stramonium. 3- Mucronate: Acute, terminating in a sharp point (apiculus), e.g. Senna. 4- Emarginate: With an acute apical notch, e.g. Jaborandi. VI- Base of the lamina: The base of a leaf is the lower part of the lamina, where it is attached to the petiole or stem. It may be: 1- symmetrical: equal on both sides as Coca 2- asymmetrical: unequal on both sides as Senna 3- decurrent: continuous downwards as wings along the petiole as Digitalis 4- Cordate bases are heart-shaped, as in Smilax V- Venation of the lamina: The lamina is traversed by vascular strands these form the veins; these are generally project on the lower side of the leaf. The disposition and arrangement of the veins. This may be: 1- Parallel: Veins are almost equal in size run side by side, parallel to each other, it may be parallel longitudinal venation as Zea or parallel transverse venation as Musa. 2- Reticulate: the lateral veins branch off into smaller veins and veinlets forming a network appearance. When lateral veins extend from main vein, called midrib, to the margin at frequent intervals and in a regular manner, it is described as pinnately reticulate (Duranta). When there is no midrib, but instead there are several divergent main veins running from base to apex, venation is described as palmately reticulate (Ricinus). VI- Surface of the lamina: Colour: upper surface is always darker in color. The length is measured from base to apex and width is measured at broadest part. Surface may be: a) Smooth: b) Glabrous: free from hairs. c) Hairy: showing covering trichomes. d) Papillosed: bearing papillae (minute, nipple-shaped protuberances). e) Pubescent: covered with erect hairs (especially soft and short ones). f) Punctate: marked with dots, dotted with depressions or with oil glands).  FIRST UP CONSULTANTS THANK YOU Dr. Amr Kotb 28