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Questions and Answers
What type of leaf does NOT have a petiole?
A simple leaf is characterized by having multiple divided blades.
False
What is the term used for the central axis of a compound leaf?
rachis
A leaf that may be cut into lobes but does not reach the vein is known as a ______ leaf.
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Match the following types of leaves with their descriptions:
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Which of the following types of leaves are primarily involved in food manufacturing through photosynthesis?
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Scale leaves are typically green due to the presence of chlorophyll.
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What is the term used for the arrangement of leaves on a stem?
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The _______ is the part of the leaf that connects the blade to the twig.
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Match the following types of leaf arrangements with their descriptions:
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Study Notes
Leaf Origin and Definition
- A leaf is a lateral outgrowth from a plant stem.
- It's typically a flattened, expanded, and variably shaped green organ.
- Its primary function is food manufacture through photosynthesis.
Types of Leaves
1- Foliage Leaves
- These are the usual green leaves performing normal leaf functions.
2- Prophylls (Fore-leaves)
- These are the first leaves on the main stem.
- They are reduced and simple in structure.
3- Bracts
- These are specialized leaves that, in their axil, either house a single flower or numerous flowers.
- They are small, simple in structure, and may be colored.
4- Scale Leaves
- These leaves are found in subterranean and some aerial stems.
- They are membranous and lack chlorophyll.
- They can be leathery and cover winter buds or fleshy.
5- Floral Leaves
- These are parts of a flower including sepals, petals, stamens, and carpels.
6- Modified Leaves
- Whole leaves or parts of them may be modified into special structures for specific functions.
Foliage Leaves Characteristics
- The most common type of leaf.
- Typically green due to chlorophyll except in some cases.
- Yellow/orange colors are caused by pigments remaining after chlorophyll disintegration.
- Possesses medicinal effects.
Phyllotaxis
- Phyllotaxis is the arrangement of leaves on the stem.
- It categorizes into alternate/spiral, opposite, or whorled.
Alternate/Spiral
- The leaves are inserted singly at the nodes.
Opposite
- A pair of leaves develops at each node.
- Opposite decussate if the two leaves in a pair position themselves at right angles to the pair above and below.
Whorled
- Three or more leaves attach at each node on the stem.
Leaf Structure
- A leaf is composed of a leaf base, petiole/leaf stalk, and lamina/leaf blade.
Leaf Base
- Connecting the leaf to the stem.
- May form a tube or sheath around the stem.
- Sometimes, small lateral outgrowths called stipules emerge from the leaf base.
- Together, the leaf base and stipules protect the young axillary buds.
Petiole or Leaf Stalk
- Connects the leaf blade (lamina) to the stem.
- Carries the leaf blade to a suitable light location and conducts materials to and from the blade.
- Leaves are classified as petiolate if having a petiole or sessile if not.
Lamina or Leaf Blade
- The flat part of the leaf.
- It's usually green.
- The lamina can be categorized as Simple, Lobed or divided, and Compound.
1- Simple Leaf
- Continuous, undivided blade.
- Lamina can take on various shapes (lanceolate, ovate, etc.)
2- Lobed or Divided Leaf
- Lobe shape may have deep divisions.
- Divisions do not typically reach the vein.
- Ex: palmately lobed, pinnately lobed
3- Compound Leaf
- Divided into several leaflets arranged along a central axis (rachis).
- Types: Binate (2 leaflets), Ternate (3 leaflets), Palmate (5 or more leaflets radiating from a common base), Pinnate (leaflets arranged on either side of a rachis)
- Paripinnate (ends in two leaflets)
- Imparipinnate (ends in a single leaflet)
- Bi-pinnate (two pinnate)
General Description of the Lamina
- Shape (e.g., lanceolate, ovate)
- Base (e.g., symmetric, asymmetric, decurrent)
- Apex (e.g., acute, acuminate, obtuse, emarginate, etc.)
- Margin (e.g., entire, dentate, serrate, crenate)
- Venation (e.g., parallel, reticulate, pinnately reticulate, palmately reticulate)
- Surface (e.g., smooth, punctate, glabrou, spinose, hairy)
Leaf Apex
- Acute: Two sides form an acute angle at the tip.
- Acuminate: Apex is prolonged into a point.
- Obtuse: Blunt or rounded.
- Mircronate: Acute apex with a sharp, horny point.
- Emarginate: Apex with a notch or indentation.
- Recurved: Curved outwards or backwards.
Leaf Margin
- Entire: Smooth margin.
- Dentate: Teeth point outwards.
- Serrate: Teeth point towards the apex.
- Crenate: Numerous minute rounded lobes.
Leaf Base Types
- Symmetric: Base equally shaped on both sides of the midrib.
- Asymmetric: Base unequally shaped on both sides of the midrib.
- Decurrent: Base extends downward as wings along the petiole.
Leaf Venation
- Pattern of veins.
- Types:
- Parallel: Veins run parallel to each other.
- Reticulate: Veins form a branching network.
- Pinnately reticulate: One main vein with lateral veins extending to the margin.
- Palmately reticulate: Several main veins arising from the tip of the midrib.
Leaf Surface
- The upper surface is often darker green than the lower.
- Can be classified as
- Smooth
- Punctate (dotted with projections from oil glands)
- Glabrous (free from hairs)
- Spinose (with spines)
- Hairy
Leaf Structure (Lamina)
- Leaf epidermis: Covers the upper and lower surfaces. Protective. Transparent. Coated with cuticle for reduced water loss. Epidermal cells are tabular, except for stomata allowing gas exchange.
- Mesophyll: Divided into palisade and spongy layers.
- Palisade Layer: Cylindrical cells arranged perpendicular to epidermis. Shows narrow intercellular spaces and often is interrupted by cortical tissue, but potentially continuous.
- Spongy Layer: Irregular, loosely arranged cells. Contains fewer chloroplasts; numerous intercellular spaces for gas exchange; linked to outside through stomata. Layer arrangement may distinguish between isobilateral and dorsiventral leaves.
- Veins: Contain vascular bundles (xylem and phloem). Xylem brings water, phloem glucose produced via photosynthesis. Vascular bundles typically appear in cross-section as an arc, with phloem toward the underside and xylem toward the upper.
- Cortical Tissue: Present mainly in the midrib region. Can consist of parenchyma or collenchyma or a combination.
- Endodermis: The inner most layer of the cortical tissue. Can take the form of a starch sheath.
- Pericycle: Lies between phloem and cortical tissue. Composed mainly of parenchyma, and sometimes of collenchyma or lignified fibers.
Leaf Hairs (Trichomes)
- Protrusions from the epidermis in many species, variable in size, and shape.
- Types:
- Papillae: Short, conical projections.
- Trichomes/hares: Larger, well-protruding projections. (can be non-glandular or glandular)
- Non-glandular hairs:
- (covering type): Uni-cellular/Multicellular. Can be Uniseriate/Bi-seriate/Pluri-seriate (row form). Further categorized by branched/unbranched structure.
- Glandular hairs: (secretory function): Unicellular/Multicellular. Classified based on stalked structure.
Stomata
- Small pores in leaf epidermis.
- Occur on both or only lower surfaces of leaf to allow in/out of gases.
- The pore is central.
- Two guard cells are found symmetrical to the pore in dicots. Different in monocots.
- Types: (based on subsidiary cell arrangement)
- Ranunculaceous
- Rubiaceous
- Caryophyllaceous
- Cruciferous
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Description
Test your knowledge about the various types of leaves, their structures, and functions. This quiz covers topics such as petioles, leaf arrangements, and the role of leaves in photosynthesis. Perfect for students of botany or anyone interested in plant biology.
