Basic BotanyTulsa County Master Gardeners

2014

Robyn Stroup

Botany – the scientific study of plant life

Plants are essential to life on earth.

They are the primary food source for humans and other animals.

Plants also: • Provide fuel• Replenish the earth’s oxygen supply• Prevent soil erosion• Slow down wind movement• Cool the atmosphere • Provide wildlife habitat• Supply medicinal compounds• Beautify our surroundings

Classification Based on shared characteristics.

Domain Kingdom Division or Phylum Class Order Family Genus Species

18th century botantistCarolus Linnaeus

Kingdom Plantae Division Tracheophyta - vascular plants Class Gymnosperms - naked seed plants Class Angiosperms - enclosed seed plants Subclass Monocots – one seed leaf Subclass Dicots – two seed leaves

species name = genus name and specific epithet

Gaillardia aristata - common blanket flower

Our focus will be on

• Vascular plants—those that contain water-, nutrient-, and food-conducting tissues called xylem and phloem.

• Ferns and seed-producing plants fall into this category.

Plant life cycles

• Annual – completes life cycle in one year. Summer or winter annuals.• Biennial – requires all or part of 2 years During the first season, it produces vegetative structures (leaves) and food storage organs.

Plant overwinters and then producesflowers, fruit, and seeds during its secondseason.

• Perennial - plants live more than 2 years

Herbaceous perennials- soft, nonwoody stems that generally die back to the

ground each winter.

Woody perennials – woody stems that withstand cold temperatures.

Monocots and DicotsNeed to distinguish between monocotyledonous (monocots) and dicotyledonous (dicots) plants. • Monocots (grasses) produce only one seed leaf

(one cotyledon).• Dicots (broadleaf plants) have two seed leaves (two cotyledons). • Other differences will be discussed.

Plant Cells

• Cells – have a cell wall that provides rigidity as long as internal water pressure exists.– Each cell contains the DNA of the cell.– Specialized cells carry out various functions

necessary to support entire plant.• Meristems – cells with rapid growing

potential. Controlled by complex plant hormones.

Functions of Roots

• Absorb nutrients and water. • Anchor the plant in the soil. • Support the stem. • Store food.

Root Structure

• Meristematic zone is at the tip and manufactures new cells - cell division and growth.

• Zone of elongation – behind the meristematic zone.

Cells increase in size. Push the root through the soil. • Zone of maturation - directly beneath the stem.

Cells become specific tissues such as epidermis, cortex, or vascular tissue.

Monocot Dicot

Root Hairs

• Root hairs are delicate, elongated epidermal cells that occur in a small zone just behind the root’s growing tip.

• Generally appear as fine down to the naked eye. • Increases the root’s surface area and absorptive capacity. • Root hairs usually live 1 or 2 days. • When a plant is transplanted, they are easily torn off or may

dry out.

Factors in root growth• Roots in water-saturated soil do not grow well and may die due to lack of oxygen. • Roots penetrate much deeper in loose, well-drained soil. • A dense, compacted soil layer can restrict or terminate root growth. • Container plants have a restricted area for root growth, also susceptible to cold damage due to limited amount of soil around roots. • Roots also grow laterally and often extend well beyond a plant’s dripline. Keep in mind when disturbing the soil around existing trees and shrubs

Stems

• Stems support buds and leaves. • Serve as conduits for carrying water, minerals, and food

(photosynthates). • Vascular system inside the stem forms a continuous

pathway from the root, through the stem, and finally to the leaves.

• It is through this system that water and food products

move.

Vascular System

• This system consists of xylem, phloem, and vascular cambium. • Think of as a plant’s circulatory system. • Xylem tubes conduct water and dissolved minerals. • Phloem tubes carry sugars (product of photosynthesis). • Cambium is a layer of meristematic tissue that separates the

xylem and phloem.

Cambium

• Cambium continuously produces new xylem and phloem cells thus increasing a stem’s girth.

• Important to gardeners. – The tissues on a grafted scion and rootstock need

to line up. – Careless weed trimming can strip the bark off a

tree, thus injuring the cambium and causing the tree to die.

Monocots & Dicots

• The vascular systems of monocots and dicots differ. These structures are arranged differently in each.

• Monocots - xylem and phloem are paired in bundles, which are

dispersed throughout the stem. • Dicots – the vascular system is said to be continuous because it forms

rings inside the stem.

Phloem forms the outer ring and eventually becomes part of the bark in mature woody stems.

Xylem forms the inner ring. In woody plants, it is calledthe sapwood and heartwood.

Stems, Nodes and Internode Space

• A node is an area on a stem where buds are located.

• Small buds develop into leaves, stems, or flowers.

• When pruning, it is important to locate a plant’s nodes.

Generally, you want to make a pruning cut just above, but not too close to, a node.

This encourages the buds at that node to begin development and ultimately form new stems or leaves.

Internodes

• The area between two nodes is called an internode.

• Its length depends on many factors, including genetics.

• Several other factors also can influence internode length:

Reduced soil fertility decreases internode length.High-nitrogen fertilizer can greatly increase it.

Lack of light increases internode length and causes spindly stems. Known as stretch, or etiolation. Often occurs in seedlings started indoors and in houseplants.

Internodes contd.

• Internode length also varies with the season. Early-season growth has long internodes.

Late-season growth generally has much shorter internodes.

• If a stem’s energy is divided among three or four side stems, or is diverted into fruit growth and development, internode length is shortened.

• Plant growth regulator substances and herbicides also can influence internode length

All stems have nodes, roots do not.

• Specialized above ground stems: stolons. Ex. strawberry runners.

• Specialized below-ground stems: tubers (potatoes), rhizomes (Bermuda grass), bulbs (tulips). All store food for the plant.

Trees and Shrubs

• Trees have one main trunk. Usually are more than 12 feet tall.

• Shrubs have several main stems. Usually are less than 12 feet tall.

• Woody stems contain relatively large amounts of hardened xylem tissue in the central core (heartwood or sapwood).

• Herbaceous stems contain only a little xylem tissue and usually live for only one growing season.

• Perennial plants - new herbaceous stems develop from the crown (root–stem interface) each year.

Buds

• A bud is an undeveloped shoot from which leaves or flower parts grow. Rest temperature may be critical.

• Buds are named for their location on the stem.

– Terminal buds are located at the apex (tip) of a stem.

– Lateral (axillary) buds are located on the sides of a stem and usually arise where a leaf meets a stem (an axil).

Leaves

• Principal function of leaves is to absorb sunlight to manufacture plant sugars through a process called photosynthesis.

• Leaf surfaces are flattened to present a large area for efficient light absorption.

• A leaf is held away from its stem by a petiole attached at a node.

Leaf Structure

• A leaf blade is composed of several layers.

• Top and bottom layers are thick, tough cells called the epidermis. Protects the other layers of leaf tissue.

• Cuticle is part of the epidermis. Waxy cutin protects the leaf from dehydration and disease. Amount of cutin on a leaf increases with light intensity. Also repels water.

Leaf Structure contd.

• Mesophyll - located between the upper and lower epidermis.

• It is divided into a dense upper layer (palisade mesophyll) and a lower layer that contains lots of air space (spongy mesophyll ).

• Located within the mesophyll cells are chloroplasts , where photosynthesis takes place

Stomata• Stomata – openings controlled by guard cells, special

epidermal cells. Water, oxygen, and carbon dioxide passed into and out of the leaf.

Guard cells - open and close in response to environmental stimuli.

Close in high temperature, low humidity. Open in mild weather. Close in absence of light.

• The majority of the stomata are on the undersides of leaves.

Types of Leaves• Foliage - most common and conspicuous, site of photosynthesis.

• Modified leaves:

– Scale leaves are found on rhizomes and buds. Enclose and protect.

– Seed leaves (cotyledons) - store food for the developing seedling.

– Spines and tendrils - protect or help support stems.

– Storage leaves - store food and water.

– Bracts - often are brightly colored. Ex. poinsettia “flowers.”

Modified leaf - bract

Modified leaf - tendril

Leaf Venation

• Veins - vascular bundles of xylem and phloem extend from the stem, through the petiole, and into the leaf blade.

• Two principal types of venation:

Parallel-veined leaves - numerous veins run essentially parallel to each other. Monocots.

Net-veined leaves - veins branch from the main rib or ribs and subdivide into finer veinlets. Allows for resistance to tearing. Dicots.

Leaf as Plant Identification

Two types of leaves:

• Simple - the leaf blade is a single, continuous unit.

• Compound - several separate leaflets arising from the same petiole.

Leaf type can be confusing because a deeply lobed simple leaf may look like a compound leaf.

Leaf Arrangement

• Opposite - leaves are positioned across the stem from each other, leaves at each node.

• Alternate -(spiral) leaves are arranged in alternate steps along the stem, only one leaf at each node.

• Whorled - leaves are arranged in circles along the stem

Leaf Edge

Flowers• Sexual reproduction as their sole function.

• Fragrance and color attract pollinators (insects or birds).

• Stamen (male flower part) - anther (pollen sac) and supported by a filament.

• Pistil (female flower part) - stigma supported by the style. Ovary contains eggs, which reside in ovules. If pollination occurs, the ovule develops into a seed.

• Accessory parts such as sepals, petals, and nectar glands

Sepals are small, green, leaf-like structures located at the base of a flower - protect the flower bud. Collectively - the calyx.

• Petals - may contain perfume. • Collectively – a corolla• The number of petals on a flower often is used

to help identify plant families and genera.

– Dicots - multiples of four or five sepals and/or petals.

– Monocots - multiples of threes.

Often forgotten!

• Monoecious plants - separate male and female flowers on the same plant. Usually self-pollinating

• Dioecious species - separate male and female plants. Male and female plants must be planted close enough together for pollination to occur.

Important pollinator!!!!

Pollination• Transfer of pollen from an anther to a stigma, by wind or by pollinators.

• Pollen will grow a long tube down the style to the ovules inside the ovary. When pollen tube reaches the ovules, it releases sperm, and fertilization typically occurs.

• Fertilization is the union of a male sperm nucleus from a pollen grain with a female egg. The ovule develops into a seed.

• Pollination is no guarantee that fertilization will occur.

• Cross-fertilization combines genetic material from two parent plants.

• The resulting seed has a broader genetic base. Usually are more successful.

Fruits

• Fertilized, mature ovules (seeds) plus the ovary wall.

Some seeds are enclosed within the ovary (ex. apples).

Some seeds are situated on the outside of fruit tissue (ex. strawberries).

SeedsContain all of the genetic information needed to develop into an entire plant.

• Embryo is a miniature plant in an arrested state of development.

• Endosperm is a built-in food supply.

• Seed coat - protects the seed from disease and insects. Also prevents water from entering the seed and initiating germination before the proper time.

Scarification is used to break or soften the seed coat. Heat of a forest fire, digestion of the seed by a bird or mammal, or partial breakdown of the seed coat by fungi or insects.

Embryo dormancy is common. Seeds must go through a chilling period before germinating. Stratification - storing seeds in a moist medium (potting soil or paper towels) at temperatures between 32 ° and 50 °F. Required length of time varies by species.

• Seed’s age greatly affects its ability to germinate.

• Older seed is less viable. If it does germinate, the seedlings are less vigorous and grow more slowly.

• The seedbed must be properly prepared and made up of loose, fine-textured soil.

• Seeds must be planted at the proper depth. Too shallow, may wash away. Too deep, won’t be able to push through the soil.

• Seeds must have a continual supply of moisture; however, if over-watered, they will rot.

Photosynthesis

• A plant requires energy from the sun, carbon dioxide from the air, and water from the soil.

Carbon dioxide + Water + Sunlight => Sugar + Oxygen

• Photosynthesis occurs only in the chloroplasts.

• Chloroplasts are incredibly small. One square millimeter, about the size of a period on a page, would contain 400,000 chloroplasts.

• Chlorophyll, the pigment that makes leaves green, is found in the chloroplasts. It traps light energy from the sun.

• If any light, water, and carbon dioxide—is lacking, photosynthesis stops.

Photosynthesis contd.

• Carbon dioxide enters a plant through its stomata.

• Photosynthesis fluctuates throughout the day as stomata open and close.

Typically, they open in the morning, close at midday, reopen in late afternoon, and close in the evening.

• Temperature - occurs at its highest rate between 65°and 85°F and decreases at higher or lower temperatures.

Respiration• Carbohydrates made during photosynthesis are converted to

energy. This energy is used for cell growth and building new tissues. The chemical process by which sugars are converted to energy is called respiration.

Sugar + Oxygen => Carbon dioxide + Water + Energy

• Essentially the opposite of photosynthesis. Photosynthesis is a building process, while respiration is a breaking-down process.

• Respiration not dependent on light. Occurs 24/7.

• Respiration occurs in all life forms and in all cells.

Transpiration• When guard cells shrink, its stomata open, and water vapor is

lost.

• In turn, more water is pulled through the plant from the roots.

• Rate of transpiration directly related to stomata being open or closed.

• Stomata account for only 1 percent of a leaf’s surface but 90 percent of the water transpired.

• Transpiration is a necessary process and uses about 90 percent of the water that enters a plant’s roots.

• The other 10 percent is used in chemical reactions and in plant tissues.

• Water moving via the transpiration stream is responsible for several things:

- Transporting minerals from the soil throughout the plant.

- Cooling the plant through evaporation.- Moving sugars and plant chemicals.- Maintaining cell turgor.

• Amount and rate of water loss depends on factors such as temperature, humidity, and wind or air movement.

• Greatest in hot, dry, windy weather.

Environmental Factors

Light: quantity, quality and duration

Quantity - intensity or concentration of sunlight.

Quality - wave-length of light. Sunlight supplies the complete range of wavelengths. Blue light is responsible primarily for leaf growth. Red light, combined with blue light, encourages

flowering Duration - photoperiod - to the amount of time a plant is exposed to light. Controls flowering in many plants.

• It’s actually the length of uninterrupted darkness that is critical to floral development!

• Short-day plants (long night) form flowers only when day length is less than about 12 hours.

• Long-day plants (short night) form flowers only when day length exceeds 12 hours.

• Day-neutral plants form flowers regardless of day length.

Temperature• Influences most plant processes - photosynthesis,

transpiration, respiration, germination, and flowering.

• As temperature increases (up to a point), photosynthesis, transpiration, and respiration increase.

• When combined with day length, temperature also affects the change from vegetative (leafy) to reproductive (flowering) growth.

• Depending on the situation and the specific plant.

Water• Growing plants contain about 90 percent water.

• Primary component in photosynthesis and respiration.• Responsible for turgor pressure in cells.• Carries minerals and carbohydrates throughout the plant.• Responsible for cooling leaves as it evaporates during

transpiration.• Regulator of stomatal opening and closing, thus controlling

transpiration, and, to some degree, photosynthesis.• Source of pressure to move roots through the soil.• Medium in which most biochemical reactions take place.

Plant HormonesProduced naturally by plants. Plant growth regulators applied by humans – may be natural or synthetic. 5 groups:

Auxin:

• Bending toward a light source (phototropism)• Downward root growth in response to gravity (geotropism)• Promotion of apical dominance• Flower formation• Fruit set and growth• Formation of adventitious roots

Gibberellins:• stimulate cell division and elongation • break seed dormancy• speed germination

Cytokinins:• found in both plants and animals • stimulate cell division • used in media for tissue culture

Ethylene Gas• induces ripening• causes leaves to droop and drop (abscission)• promotes senescence • part of the reason leaves fall off of trees• used to artifically ripen fruit

Abscisic acid (ABA) • general plant-growth inhibitor • induces dormancy• prevents seeds from germinating• causes abscission of leaves, fruits, and flowers• causes stomata to close

Any Questions?

Thank you!