Plant Morphology: Roots and Stems

• Plant morphology is the study of the physical form and external structure of plants
• It is concerned with the description, comparison, classification, and understanding of plant forms

Roots

• Roots anchor the plant, absorb water and nutrients, and store food
• The primary root is the first root to emerge from a seed
• It can develop into a taproot, which is a large, central root
• Lateral roots branch out from the primary root
• Adventitious roots arise from stems or leaves, not from the primary root
• Root hairs are tiny extensions of root epidermal cells that increase the surface area for water and nutrient absorption
• Root caps protect the root tip as it grows through the soil

Stems

• Stems provide support for the plant and transport water, nutrients, and sugars
• They connect the roots to the leaves and flowers
• Stems can be herbaceous (soft and green) or woody (hard and covered with bark)
• Nodes are the points on a stem where leaves or branches are attached
• Internodes are the regions between nodes
• Buds are undeveloped shoots that can develop into leaves, flowers, or branches
• Terminal buds are located at the tip of the stem
• Axillary buds are located in the leaf axils (the angle between a leaf and the stem)
• Lenticels are small pores on the stem that allow for gas exchange

Leaves

• Leaves are the primary photosynthetic organs of plants
• They capture sunlight and convert it into energy through photosynthesis
• Leaves typically consist of a blade (the broad, flat part of the leaf) and a petiole (the stalk that attaches the blade to the stem)
• Simple leaves have a single, undivided blade
• Compound leaves have a blade that is divided into leaflets
• Leaf venation refers to the pattern of veins in a leaf
• Parallel venation is characteristic of monocots
• Netted venation is characteristic of dicots
• Leaf arrangement can be alternate, opposite, or whorled

Flowers

• Flowers are the reproductive structures of angiosperms (flowering plants)
• They are responsible for producing seeds
• A typical flower consists of four main parts: sepals, petals, stamens, and carpels
• Sepals are the outermost parts of the flower, and they protect the developing bud
• Petals are usually brightly colored to attract pollinators
• Stamens are the male reproductive organs, and they consist of an anther (where pollen is produced) and a filament (a stalk that supports the anther)
• Carpels are the female reproductive organs, and they consist of an ovary (where ovules are located), a style (a stalk that connects the ovary to the stigma), and a stigma (the sticky surface that receives pollen)
• A complete flower has all four parts (sepals, petals, stamens, and carpels)
• An incomplete flower is missing one or more of these parts
• A perfect flower has both stamens and carpels
• An imperfect flower has either stamens or carpels, but not both
• Inflorescences are clusters of flowers

Fruits

• Fruits develop from the ovary after fertilization
• They protect the seeds and aid in their dispersal
• Simple fruits develop from a single ovary
• Aggregate fruits develop from multiple ovaries in a single flower
• Multiple fruits develop from multiple flowers in an inflorescence
• Accessory fruits are fleshy parts that are derived from tissues other than the ovary
• Dry fruits can be dehiscent (splitting open to release seeds) or indehiscent (not splitting open)

Seeds

• Seeds are the mature ovules that contain the embryo of a new plant
• They are typically surrounded by a protective seed coat
• The embryo consists of an embryonic root (radicle), an embryonic shoot (plumule), and one or more cotyledons (seed leaves)
• Seeds may also contain endosperm, which is a food storage tissue that nourishes the developing embryo

Plant Tissues

• Plant tissues are groups of cells that perform specific functions
• There are three main types of plant tissues: dermal tissue, ground tissue, and vascular tissue

Dermal Tissue

• Dermal tissue forms the outer protective layer of the plant
• The epidermis is the outermost layer of cells in the dermal tissue
• It is covered with a waxy cuticle that helps to prevent water loss
• In woody plants, the epidermis is replaced by the periderm, which is a tough, protective layer of bark

Ground Tissue

• Ground tissue makes up the bulk of the plant body
• Parenchyma cells are the most common type of ground tissue cells
• They are responsible for photosynthesis, storage, and other metabolic functions
• Collenchyma cells provide flexible support to the plant
• Sclerenchyma cells provide rigid support to the plant
• They often contain lignin, a strengthening polymer

Vascular Tissue

• Vascular tissue transports water, nutrients, and sugars throughout the plant
• Xylem transports water and minerals from the roots to the rest of the plant
• The cells are dead and hollow at maturity
• Phloem transports sugars from the leaves to the rest of the plant
• The cells are alive at maturity

Plant Cell Types

• Parenchyma cells are fundamental and versatile, performing a wide range of functions from photosynthesis and storage to secretion and wound repair
• Collenchyma cells provide flexible support to growing plant parts, allowing them to bend without breaking
• Sclerenchyma cells offer rigid support and protection to the plant, often due to the presence of lignin in their cell walls
• Xylem cells, including tracheids and vessel elements, are specialized for water transport, forming continuous pipelines throughout the plant
• Phloem cells, including sieve tube elements and companion cells, work together to transport sugars and other organic nutrients throughout the plant

Leaf Morphology

• Leaf shape, size, texture, and other characteristics vary greatly among plant species and can be influenced by environmental factors
• Leaf adaptations, such as thorns or thick cuticles, allow plants to thrive in a range of habitats
• Leaf arrangements, including alternate, opposite, and whorled patterns, maximize light capture and minimize shading
• Specialized leaves, such as bracts, spines, and storage leaves, perform unique functions beyond photosynthesis

Stem Modifications

• Rhizomes are horizontal underground stems that store food and allow plants to spread vegetatively
• Tubers are swollen underground stems that function as storage organs
• Stolons are horizontal aboveground stems that allow plants to colonize new areas
• Tendrils are modified stems or leaves that help plants climb

Root Modifications

• Prop roots are adventitious roots that provide support to the plant
• Buttress roots are large, aboveground roots that provide stability
• Pneumatophores are specialized roots that allow plants to breathe in waterlogged soils
• Storage roots are roots that are modified to store food or water

Microscopic Plant Morphology

• Plant cells are the fundamental units of plant structure and function
• Cell walls provide support and protection to plant cells
• Chloroplasts are the organelles where photosynthesis takes place
• Vacuoles are large storage organelles that contain water, nutrients, and waste products
• The nucleus contains the plant's genetic material

Variations in Plant Morphology

• Plant morphology can vary greatly depending on the species, environment, and stage of development
• Some plants have adapted to extreme environments with unique morphological features
• For example, succulents have fleshy leaves or stems that store water
• Other plants have specialized structures for pollination, seed dispersal, or defense

Importance of Plant Morphology

• Plant morphology is important for plant identification, classification, and understanding plant evolution
• It is also important for agriculture, horticulture, and forestry
• By studying plant morphology, we can learn how plants adapt to their environment and how to improve crop yields