Plant Morphology and Life Cycle

Plant Morphology and Anatomy

• Plant morphology describes the physical form and external structure of plants.
• Plant anatomy studies the internal structure of plants.

Plant Life Cycle

• Juvenile Phase:
  • Characterized by exponential growth and inability to produce flowers.
  • Plants exhibit specific morphological and physiological traits during this phase.
  • Examples:
    • Hedera helix (ivy): Immature stage has five lobes, mature stage has none.
    • Juniperus virginiana (Eastern red cedar): Young growth has thorns, older growth doesn't.
  • Physiological traits include vigorous growth, disease resistance, and greater ability to regenerate roots and shoots.
• Reproductive Phase:
  • Qualitative changes occur, allowing the plant to express its full reproductive potential.
  • Entry into this phase is determined by both genetic and environmental conditions.
• Senescence Phase:
  • Internally controlled deteriorative changes leading to natural death.
  • Changes include:
    • Decreases in chlorophyll, protein, DNA, RNA, and photosynthesis.
    • Changes in plant hormones.
  • Ends with leaf abscission.

Leaf Anatomy and Morphology

• Functions:
  • Photosynthesis: Conversion of carbon dioxide and water into carbohydrates using light and chlorophyll.
  • Transpiration: Loss of water from the leaf in the form of water vapor.
  • Respiration: Breakdown of sugars produced during photosynthesis for plant growth and development.
• Parts:
  • Petiole: Leaf stem or stalk attaching the leaf to the stem.
  • Blade: Flat, thin portion of the leaf.
  • Midrib: Largest vein located in the middle of the leaf.
  • Veins: Transport water and nutrients.
  • Leaf margin: Outer edge of the leaf blade.
  • Leaf apex: Tip of the leaf blade.
  • Leaf base: Bottom of the leaf blade.
  • Stipule: Small leaf-like appendage at the base of the leaf stalk.
• Types:
  • Simple leaf: One blade per petiole.
  • Compound leaf: Two or more leaflets.
  • Difference between leaf and leaflet: Axillary bud location (at the base of the entire leaf for a leaf, not for leaflets).
• Leaf attachment patterns:
  • Opposite: Two leaves directly across from each other (two leaves per node).
  • Alternate: Leaves staggered along the stem (one leaf per node).
  • Whorled: Three or more leaves attached per node.
• Modified leaves:
  • Bracts: Leaves located just below the flower (e.g., poinsettia, dogwood).
  • Tendrils: Appendages produced by vines that wrap around supports (e.g., grapes).

Stem Anatomy and Morphology

• Functions:
  • Support for leaves, flowers, and fruits.
  • Transportation of water, minerals, and manufactured food.
  • Food manufacturing (to a lesser extent than leaves).
  • Food storage.
• Parts:
  • Terminal bud: Located at the tip of the stem, containing undeveloped leaves, stems, flowers, or a mixture of all.
  • Bud scale: Tiny leaf-like structure covering and protecting the bud.
  • Terminal bud-scale scar: Left when the terminal bud begins growth in the spring, representing one year's growth.
  • Axillary bud: Located along the side of the stem below the terminal bud.
  • Node: Point along the stem where leaves or stems are attached.
  • Internodal region: Located between the nodes.
  • Leaf scar: Left when the leaf drops.
  • Lenticels: Tiny pores in the stem used for gas exchange.
• Internal Anatomy:
  • Epidermis: Outer layer of the stem.
  • Cortex: Primary tissue located between the epidermis and vascular region.
  • Cambium: Area where new plant cells (xylem or phloem) are formed during secondary growth.
  • Xylem: Transports water and nutrients up from the roots.
  • Phloem: Transports manufactured food and carbohydrates down from the leaves.
  • Pith: Center portion of the stem, storing food and moisture.
• Modified Stems:
  • Stolon: Aboveground horizontal stem with long and thin internodes (e.g., strawberry runners).
  • Rhizome: Belowground horizontal stem (e.g., ginger root, turmeric).
  • Tuber: Underground rounded swelling of a stem (e.g., Irish potatoes).
  • Corm: Vertical, thick stem with thin, papery leaves (e.g., gladiolus).
  • Bulb: Short shoot with thick, fleshy leaves (e.g., onions, tulips).

Root Anatomy and Morphology

• Functions:
  • Absorption of water and nutrients.
  • Storage of carbohydrates.
  • Anchorage and support for the top portion of the plant.
• Parts:
  • Primary root: Main root emerging from the seed.
  • Root cap: Protective layer of cells at the tip of the root.
  • Area of cell division: Just behind the root cap.
  • Area of cell elongation: Following the area of cell division.
  • Area of maturation or cell differentiation: Final stage of root development.
  • Secondary root: Arises from the primary root.
  • Root hairs: Single cells responsible for most water and mineral absorption.
• Root Systems:
  • Taproot system: Primary root grows down from the stem with a few secondary roots (common in dicots, e.g., carrots, dandelions).
  • Fibrous root system: Many small primary and secondary roots (common in monocots, e.g., potato plants, grasses).
• Modified roots: Serve as food storage (e.g., sweet potatoes).

Flower Anatomy and Morphology

• Functions:
  • Attracting pollinators.
  • Production of fruit and seed.
• Parts:
  • Sepals: Green, leaf-like structures located beneath the petals.
  • Calyx: Name for all the sepals on a flower.
  • Petals: Brightly colored portions of the flower that attract pollinators.
  • Stamens: Male reproductive parts, composed of a filament and anther.
  • Anther: Produces pollen (male sex cells).
  • Pistils: Female reproductive parts, composed of stigma, style, and ovary.
  • Stigma: Sticky surface for collecting pollen.
  • Style: Tube connecting the stigma and ovary.
  • Ovary: Contains ovules or eggs.
• Flower Types:
  • Complete: Contains all four major flower parts.
  • Incomplete: Lacks one or more major flower parts.
  • Perfect: Contains both stamens and pistils.
  • Imperfect: Lacks either stamens or pistils.
• Flower Part Multiples:
  • Monocots: Multiples of 3.
  • Dicots: Multiples of 4 or 5.

Fruit Anatomy and Morphology

• Definition: Mature ovary of a flowering plant.
• Types:
  • Fleshy: Soft fleshy material with or without seeds enclosed (e.g., tomato).
  • Dry: Seeds enclosed in a hard fruit wall (e.g., sunflower).
• Informal Definition: Something that is sweet.

Seed Anatomy and Morphology

• Definition: Mature fertilized egg contained in the fruit.
• Dispersal: Wind, animal fur, etc.
• Food Storage:
  • Dicots: Cotyledons.
  • Monocots: Endosperm.

Seed Germination

• Criteria for Germination:
  • Seed must be viable (embryo alive and capable of germination).
  • Appropriate environmental conditions.
  • Primary dormancy in the seed must be overcome.
• Stages:
  • Imbibition: Active uptake of water by the seed.
  • Enzyme activation: Preexisting and newly produced enzymes break down storage reserves for germination.
• Forms:
  • Epigeous: Hypocotyl elongates, bringing the cotyledons above ground (e.g., cherries).
  • Hypogeous: Epicotyl emerges, cotyledons remain below the soil surface (e.g., corn).

Monocot vs. Dicot Differences

• Monocot:
  • One cotyledon.
  • Parallel leaf veins.
  • Scattered vascular bundles in the stem.
  • Fibrous root system.
  • Flower parts in multiples of three.
• Dicot:
  • Two cotyledons.
  • Netlike (reticulate) leaf veins.
  • Vascular bundles usually arranged in a ring in the stem.
  • Taproot system.
  • Flower parts in multiples of four or five.

Conclusion

• Understanding plant anatomy and morphology, including vegetative and reproductive structures, is crucial for plant classification and maximizing their potential uses.