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Demystifying

Plants:Botany for

Gardeners

Plants in our Ecosystem

• Capture sun’s energy

• Food source

• Replenish atmospheric oxygen

• Participate in water cycle

• Moderate world climate

• Provide shelter

• Source of numerous raw materials

• Support a myriad of other living things

When scientists study plants,

what do they study?

• The way plants grow and function (plant

morphology and physiology)

• The way plants are genetically related to each

other (plant taxonomy)

• How plants interact with their natural

environment (plant ecology)

• How plants evolve and adapt to the environment

at a gene and molecular level (plant genetics)

Horticulture = Botany applied

• Identify plants

• Grow & propagate plants

• Influence flowering & fruit

production

• Control unwanted growth

• Maintain plant health

• Modify plant features through

breeding and selection

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Horticulture is the study of

useful plant oddities

In disturbed, reorganized, and

coddled landscapes

Variegated Norway maple

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Plants don’t live in isolation

• Physical environment

(soils, climate,

moisture, etc.)

• The living

environment (other

plants, people,

animals, insects,

fungi, etc.)

Plant communities are always

changing

• This is called plant

succession

• Examples from

native landscapes

• Examples from

gardening

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Horticultural plant classifications

• Sun or shade

• Acid or neutral or alkaline soils

• Drainage preference

• Growth habit (woody vs. herbaceous; tree

vs. shrub; evergreen vs. deciduous; etc.)

• Cold hardiness

• Reproductive strategy: annual, biennial,

perennial.

• Plant family

How do plants get through

winter?

Climate zones define the average low winter temperatures for large areas.

Your property may be in a micro-climate that differs (either warmer or colder) from the general cold winter pattern for your region.

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The importance of life cycles

• Annuals– winter

– summer

• Biennials

• Perennials

– Herbaceous

– Woody

• deciduous

• evergreen

Winter annuals

• Spread exclusively by

seeds that germinate in

the fall/winter and go to

seed in the spring to early

summer and die.

• Some, in this climate, grow

year round

• Examples: chickweed,

groundsel, red dead

nettle Groundsel – Senecio vulgaris

Summer annuals

• Also spread by seed

that germinate in the

spring and summer

• Flower and seed by

fall and die

• Compete with

vegetable crops

• Examples: pigweed,

lambsquarter, and… Purslane

Biennials

• Spread by seed that

germinate in spring-fall

• Overwinter as a

“rosette”

• Flower and seed next

year in the late spring-

summer and die

Bull thistle – Cirsium vulgare

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Herbaceous perennials

• Tops die back

• New shoots each

spring from

roots/crown

• Spread by seed

and vegetative

pieces and don’t

die

Hedge bindweed Calystegia sepium

aka Morning glory

Woody perennials• Tend to spread by

seeds.

• Some vegetative

spread with some

species e.g. ivy,

& root suckers on

some trees. We

propagate by seed,

cuttings, grafting, etc

• Don’t die

Classifying plants into families

• Why do we care?

• What are the key

botanical characteristics

used? Why?

Why flowers?

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Linnean classification of plants

• Lower vs. higher plants

• Gymnosperms (conifers

and others) and

Angiosperms

• Monocots and dicots

• Family: Aceracea

• Genus: Acer

• Species: rubrum

• Cultivar: Autumn Blaze

Summary of differences, monocots & dicots

Chloroplasts capture light energy

CO2 + H20 + light energy = sugars + O2

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What are the requirements for

plant growth?Light energy

Heat (some)

Stored energy

Water

Carbon, hydrogen, oxygen

Mineral elements

A few other important concepts

• Meristems

• Plant

hormones

Meristems

• Areas of actively

dividing cells

that develop into

plant tissues

and organs

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Plant hormones aka plant growth

regulatorsChemicals present in

tiny quantities that

affect plant

development and

response to

environment including

dormancy, growth rate,

fruit, flowering, etc.

Plants have to start from

something

Dr. B. Rathinasabapathi - U. Florida

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Seed Anatomy

• Embryo - miniature plant in an arrested state of development

• Endosperm - food supply (can be comprised of proteins, carbohydrates, fats)

• Seed coat - hard outer covering that protects from disease and insects; also repels water

• Temperate seeds measure winter temperatures

Cut away seed

• Seed is a dicot with

two seed leaves

• Root apex at lower

left

• Root connected to

hypocotyl where

cotyledons are

attached

• Seed coat

• Endospeerm

Seeds and Seedlings Seed germination requirements

• Activation of embryo

within seed

• Preceded by water

penetrating seed coat

• Oxygen, favorable

temperature cycle, and

(in some species) light

required

• Other cues

.

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Other germination factorsDicot

Monocot

Cotyledons = modified leaves

beandicot seed = 2 cotyledons

monocot seed = 1 cotyledon

cotyledons

first true leaves

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Vascular system (“plumbing”)

Root functions

• Anchors the plant

• Absorbs water and

minerals

• Stores food

• Reproductive organ

• Compete with other

plants for water and

minerals

Root Structure

Lateral Root

Primary Root

Root Hairs

Root Tip

Root Cap Meristematic Zone

Zone of Elongation

Zone of

Maturation

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Meristematic Zone

Root Cap

Root Tip

Zone of Elongation

Photo: Source Unknown

Tap Root Fibrous Root

Dicots

Monocot

Modified roots

Tuberous root – sweet potato Storage root of beet

Tuberous root, dahlia Storage root – carrot

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Root Anatomy

Epidermis

Cortex

Endodermis

Xylem

Phloem

Photo: Botany for Gardeners, Capon

What’s inside a root?

buttercup

The vascular system is in the center

What’s inside a root?

buttercup

xylemcortex

phloem

cambium in woody roots

Root Tissues

• Xylem - conduct water & nutrients

• Phloem - carry sugars & starches

• Endodermis - contain vascular tissues

• Cortex - primary tissue surrounding vascular bundle

• Epidermis - outermost layer of plant tissues, protective layer

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Unique to roots!

root cap -located at root tip & protects growing point

Origin of lateral roots

Notice the root cap on the lateral root –cut away section

Root hairs on a radish seedling

Root hairs absorb most of the water a plant gets –very tiny

Root hair cross-section

• delicate

• thin-walled

• room for lots of water

• has lower water pressure than the outside soil

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Let’s review Mycorrhizae = fungal partners

on/in higher plant roots

Mycorrhizal fungus

Which partner gets what?

How much water do these plants move?

Corn Big leaf maple

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Factors influencing root growth

• Light captured

• Gravity

• Temperature

• Soil texture

• Oxygen

• Moisture

• Minerals

• Salt

Storms happen

and so do shallow

roots

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Root spread

Issues: construction, covering & stability

certain herbicides problems

yard invasion and suckering

other problems

What does a stem do?

Physically support leaves, buds, flowers & fruits

Transport water, minerals & sugars and other compounds

Provides storage in some plants

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What’s inside the stem?

cortex cells add structural strength to the stem

vascular bundles

corn

Vascular bundle arrangement

herbaceous dicot (sunflower)

Phloem

Xylem

Vascular bundle

Phloem transports photosynthetic products to areas of the plants needing energy

Xylem is like tiny straws and transports water and minerals from the soil to other parts of the plant and out through the leaves

Vascular cambiumcells make more xylem and phloem

Vascular cambium

• Cambium is a meristematic tissue,

meaning it divides to produce new tissues

• Cambium divides to produce

– xylem: to the inside (heartwood, pith)

– phloem: to the outside (part of bark)

• Responsible for “girth growth,” or

increased stem diameter in woody plants

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Stem cross-section

Herbaceous dicot

(clover)Herbaceous monocot

(corn)

xylem

phloem

Notice the relative position of the xylem, phloem, and cambium!

cambium

Herbaceousmonocot (corn)

Stem cross-sections

Woody dicot(maple tree)

Carry H2O & dissolved nutrients

Cells are:

long, open-ended, connected end to end

have thick cell walls

resemble straws

Xylem cells

Xylem cells are really strong. Why?

P. Dahiya: Nature Cell Biology

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Phloem cells

Transport actively photosynthetic products

from leaves to roots, stems, flowers & fruits

Cells are:

long and tube-like

without extra cell wall thickening

vascular cambium

bark

phloem

xylem

What’s this area?

Woody Stem Anatomy

Vascular

Cambium

Sapwood

-

functional

xylem

Inner Bark

(phloem)

Outer Bark

Heartwood -

nonfunctional

xylem

?What is bark?

Answer. Bark is the outer layer of cells on a tree containing

cambium, compressed phloem, and sometimes, cork.

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Stems evolve in response to selection pressure

Thorns for defense (rose) Corky extensions (Euonymus alata)

Photosynthetic stems (Blueberry and Christmas cactus)

Stems selected by humans for storage

Stems evolved for vegetative propagation

External parts of the stem

node = place where leaf is

(or was) attached to

the stem

internode = distance

between nodes

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Lenticel

(breathing pore)

Bud Scale Scar

Leaf Scar

Node

Node

Node

Internode

Terminal Bud

Axillary or

Lateral Bud

Lateral or axillary buds

Located in the angle where the leaf attaches to the stem

Apical dominance

Lateral buds kept dormant due to plant hormone (auxin) cascading from top downwards until auxin source removed

Apical (apex = top) dominance

Auxin= plant growth regulator or “hormone”

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Axillary bud

May produce lateral shoot or branch –less auxin effect further from the apex due to dilution

Auxin and fruit trees

Phototropism –

another auxin effect

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Auxin

Phototropism

Buds and

vegetative

dormancy –

what triggers

the dormancy

process and

what brings

them out of

dormancy?

Winter chilling requirement – hours below 45 degrees

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Leaf Functions

• Use sunlight to make

sugars – photosynthesis

• Use sugars to make

energy and other

compounds – respiration

• Move water from roots

throughout the plant -

transpiration

Major leaf parts

• lamina (leaf blade) -highly variable in size and shape

• petiole - stalk at base of leaf that attaches leaf blade to stem

catching insects

Modified leaves

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floating spinesscales

tendrils Succulence

More modified leaves Leaves modified for storage

leaf blade

petiole

Remember monocots & dicots?

dicots monocot

Monocot or Dicot?

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Leaf arrangement on a stem

opposite

whorled

alternate

These characteristics are important in identifying plants

bedstraw Japanese knotweed

What are the leaf arrangements of these plants?

snowberry

Compound vs. Simple leaves

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Simple leaf

Buds are in the axils between leaf and stem

Compound leaves

pinnately compound palmately compound

leaflet

What’s going on inside the leaf

and plant?

• Photosynthesis

• Respiration

• Transpiration

Balancing act

What is photosynthesis?

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Chloroplasts capture light energy

CO2 + H20 + light energy = sugars + O2

Mid-rib cross-section

central vein

or mid-rib

upper epidermis

lower epidermis

Epidermis

May have special adaptations like hairs or waxy layer that help with drought tolerance

stinging nettle

Other adaptions on the

epidermis?

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Leaf cut-away

mesophyll

Stomata

Stomatal

cycle

Factors that affect

photosynthetic rate

• Carbon dioxide

availability

• Water

• Light (quality, amount,

quantity)

• Temperature

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What is transpiration?

Transpiration is water loss (as vapor) from a plant

Transpiration rate is controlled by opening and closing of the stomates, which is influenced by humidity, temperature, and time of day.

Functions of transpiration

•Cool plant

•Transport

minerals

•Move sugars &

plant chemicals

around

•Maintain turgor

What is turgor?

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Transpiration requires…

• soil moisture

• functional root system

• functional stem & branch

plumbing

• functional leaves

Transpiration Rate

• Transpiration rate is controlled by…

– stomatal aperture

• in response to…

– relative humidity

– temperature

– light

– wind

• under constraint of…

– water availability

– plant nutrition

How does water get from the soil to the top of a tree?

Stomates control evaporation

Root hairs (often with the help of mycorrhizae) absorb water from the soil

Xylem cells transport water via capillary action and cohesive force of water

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Respiration is the opposite of

photosynthesis

In respiration, sugars, water, and oxygen are used to create energy to drive biochemical reactions and carbon dioxide and water are released.

What is respiration? Factors affecting respiration rate

Temperature

Oxygen

Soil condition

Sugars + oxygen = chemical energy + CO2 + H2O

A Comparison

• occurs in sunlight

• uses food

Photosynthesis Respiration

• releases oxygen

• uses carbon dioxide

• uses water

• stores energy

• produces food

• releases energy

• produces water

• releases carbon dioxide

• uses oxygen

• occurs in dark and light

Plant Processes in Balance

• Water Uptake vs Transpiration

• Photosynthesis vs Respiration

• Carbohydrate allocation

• Nutrient allocation

• Growth vs Storage vs Reproduction

vs Defense…

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. How plants reproduce

(or are propagated by clever

gardeners)

Vegetative (asexual)

propagation

Divisions

Cuttings

Layering

Grafting/Budding

Tissue culture

Cuttings

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Responses involving auxin

Formation of

adventitious roots

Layering

Grafting Grafting

Scion

Rootstock

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Tissue cultureCytokinin and auxin & tissue

culture

Flowers and sexual propagation

Flowers facilitate pollination.

If fertilization occurs, seeds are produced and carried in cones (conifers) or fruits (flowering plants)

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The flowering response

Juvenility and flowering - apples

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Parts of a flower

Lily

Flower parts

anther

stigma

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Flower Types

• Complete – Has all floral parts present (sepals, petals, stamens, pistils)

• Incomplete -flower lacks 1 or more of the 4 parts

Flower Types, Continued

• Perfect – Has both stamens and pistils (male and female parts)

• Imperfect – Lacks either stamens or pistils

“male” flower

(staminate)

“female” flower

(pistillate)

Complete or Incomplete?Perfect or Imperfect?

Imperfect flowers can be either

monoecious (on the same plant) or

dioecious (on different plants)

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Walnut:

monoecious

Holly:

dioecious

Male and female trees

Pollination

Method: wind, insects, bats, lizards, etc.

Incompatibility: What is it and

why it has evolutionary value?

Hybrids: Mostly man-made but not always

Pollination vs. fertilization

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beetles wind hummingbirds

big leaf maple cape fuchsiawillow

butterflies flies bees

yarrow skunk cabbage cat’s ear

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Dranuculus

vulgaris

Carrion beetles

? Can you think of any modified

flowers?

Hint: think veggies!

pollen grains

ovary

pollen tube

ovule

Fertilization

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Seed dispersal

• Wind

• Water

• Animals

• Insects

• Others

Fruit: Facilitates seed dispersal

185

Seeds release hormones that cause cells to divide

and expand. When seeds are only on one side

lopsided fruit results.

Very incomplete pollination = fruit drop

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Ethylene

Fruit ripening

Five plant growth regulators

Auxins

Gibberellins

Abscisic acid

Cytokinins

Ethylene

Auxin

Apical dominance

Phototropism

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Gibberellic acid

Stimulate cell division and elongation

Speeds seed germination

Breaks seed dormancy

Abscisic acid

Induce and maintain dormancy

Control stomatal closure

Leaf abscision

Cytokinins

Stimulate cell division

Delay senescence

Ethylene

Stress response: epinasty and leaf drop

Fruit ripening

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