Plant Anatomy Week 1

7/31/2019 Plant Anatomy Week 1

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Plant anatomy

In the Plant Classification presentation we covered many practical ways of categorizing plants.

Plants are also categorized based on their anatomy. Even more valuable is the use of plant

anatomy to identify plants. Familiarity with basic plant anatomy is also important to many

management practices such as pruning and dividing plants. For most horticultural careers it isnecessary to be able to recognize and describe plant structures. Once we know the terms used

to describe the plants that we study or cultivate, we can communicate with each other and

describe plants and management practices using a common language.

Plant Structure/Terminology

Plant structures such as leaves, roots, stems, flowers,

and fruits are referred to as plant organs. Plant

organs can be separated into two categories:

reproductive organs and vegetative organs. Flowers

and fruit seeds are the reproductive organs

specialized for producing and distributing seeds.

Stems, leaves, and roots are vegetative organs. They

are involved in nutrition and growth rather thanreproduction. We may use vegetative organs to

propagate plants asexually by taking cuttings or

grafting plants. Characteristics of both reproductive

and vegetative plant parts may be used to identify and

classify plants.

Copyright Oregon State University.

internode

node


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Vegetative organs

The leaf

The primary function of the leaf is to absorb sunlight and use CO2 and water to manufacture

carbohydrates (sugars) through the process ofphotosynthesis. Leaves are usually flat to

provide a large surface area to absorb light energy. Some specialized non-foliage leaves (budscales, bracts, and sepals) are adapted to protect buds. Cotyledons (seed leaves) are

specialized leaves that store food to support the plant embryo contained in the seed. Plants

are classified as monocots or dicots based on the number of cotyledons contained in the seed.

Monocots have a single cotyledon. Dicots have two cotyledons.

There are two main structures of the leaf the blade and the petiole. The broad, thin structure

is the blade or lamina, usually the most conspicuous part of the leaf. The narrow stalk that

attaches the blade to the stem is the petiole. The part of the blade that is furthest from the

petiole is the apex. The base of the blade is the part closest to the petiole. The outer edge of a

leaf is called the leafmargin. Down the center of many kinds of leaves there is a large vein thatextends from the base to the apex. Sometimes it is easier to see it if you look at the leaf

upside-down. This big central vein is called the midrib. Smaller lateralveins extend out from

both sides of the midrib. The pattern of leaf venation may be used as a basis for classifying

plants. Dicots generally have a large single midrib with smaller veins branching out into the

blade - think of a maple leaf. This is referred to as reticulate venation. Monocots have parallel

venation. Grasses, wheat, corn, and rice are monocots.

One of the essential components of the leaf blade is the stomata, small openings in the leafsurface that can be opened and closed by the guard cells around them in response to

environmental conditions such as drought. The stomaThe leaf blade may be covered with hairs

called pubescence. All leaves have a waxy coating called cutin. The amount of cutin on a leaf

varies. It is increased by exposure to high light intensity.

Figure 2: Leaf venation

Figure 3: Stomata


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The stem-like petiole holds the blade away from the stem. Petioles vary in length and there are

some plants that lack petioles entirely. Leaves without petioles are referred to as sessile

leaves. Leaves are attached to the stem at a node. The point where the petiole connects to the

stem is called the leafaxil. The axil contains one or more buds that can develop into leaves or

stems. These buds are called axillarybuds.

The leaf at left is a simpleleafbecause the blade of the leaf

blade is a single continuous unit. Some plants have

compoundleaves with a blade broken into smaller leaflets.

Three or more leaflets are arranged at the end of the petiole

like fingers on a hand on a palmatelycompoundleaf.

Pinnatelycompoundleaves have a number of leaflets

attached along a central stalk. Some leaves are doubly

compound. Leaf type can be confusing, because a deeply

lobed simple leaf may look like a compound leaf. You can

distinguish between a leaf and a leaflet because leaves have

a bud at the base of the petiole, leaflets do not.Copyright Oregon State University.


Leaves are attached to the stem in different patterns. Alternate leaves have only a single leaf

attached at each node (a node is the point on a stem where a leaf is attached). The leaves

often the leaves alternate sides of the stem or are in a spiral pattern around the stem.

Opposite leaves are two leaves attached at node, but on opposite sides of the stem. Ifmore

than two leaves arise from the same node, radiating from the stem like spokes on wheel, this is called

a whorled arrangement.

When identifying plants, knowing the terms used to describe leaf shapes and margins is also

important. The Penn State Horticulture Dept. web site has a good source for information about

leaf arrangements, shapes, and margins http://cas.psu.edu/docs/CASDEPT/Hort/LeafID/.

Figure 4:

Figure 5:
http://cas.psu.edu/docs/CASDEPT/Hort/LeafID/http://cas.psu.edu/docs/CASDEPT/Hort/LeafID/http://cas.psu.edu/docs/CASDEPT/Hort/LeafID/


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The stem

Above the ground, the stem holds the plant upright and holds aloft the other aerial vegetativeorgans the leaves. The stem also supports the buds, flowers, and fruits, which are

reproductive organs. The stem serves as a conduit for carrying water, minerals, and food

(photosynthates). The vascular system inside the stem forms a continuous pathway between

the leaves and roots. Xylem vessels carry water and nutrients absorbed from the soil by the

roots to the above ground parts of the plant. Phloem vessels carry photosynthates

(carbohydrates produced in the green leaves) from the leaves to the rest of the plant.

The node is where buds are located on the stem. It is an area where small buds can develop

into leaves, stems, or flowers. When pruning plants it is important to be able to recognize

where the nodes are located along the stem. The space between two nodes is called the

internode. Internode length is determined genetically and by environmental conditions.

Stems may vary in length from long stems with large internodes spacing leaves and buds far

apart to crowns or rosettes with very short internodes and leaves emerging close together.

Most stems grow above ground but there are specialized underground stem structures that are

covered in the underground structure document.

Specialized stem structures

Some plants have a basal rosette. This is a short compressed stem with leaves growing from a

crown near or on the on soil surface. The crown is where the stem and roots meet. Flowersare borne on stems held above the leaves.

Figure 6:


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Missouri Plants

Plants such as strawberries spread through the growth of a stolon. A stolon is a horizontal stem

that grows along the surface of the soil and produces roots and new shoots at its tip. New

plants grow up from the new roots/shoots.

Spurs are found most commonly on fruit trees. They are stems with severely shortened

internodes. Fruit is produced from reproductive buds on the tips of spurs.

Roots

Roots originate from the crown and are the underground part of the plant or cutting. They

have a root cap but no nodes. They cannot bear leaves or flowers. The principal functions ofroots are to absorb nutrients and water, anchor the plant, support the stem, and store food.

Although roots are often overlooked it is important to understand their structure because they

have a profound effect on a plants vigor and health. Also, when dividing plants or managing

plants with specialized root structures it is important to know what type of roots your plant has.

In some plants roots can be used for propagation.

The drawing below shows a primary root or a taproot and lateral roots. Lateral roots grow out

sideways from the taproot. Root hairs are elongated epidermal cells that extend from the root

surface. Root hairs have a large surface area in contact with the soil with which they absorb

water and nutrients.

flower stem

rosette

Maines Virtual Herbarium

Figure 7: Stolon


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Some plants have fibrous roots. Rather than having a main taproot with lateral roots growing

from it, they have a number of roots that grow from the base of the stem. The roots are allabout the same size, and they do not grow as deeply into the soil as the taproot. Lateral roots

also grow from the sides of these roots.

Adventitious roots grow from tissue other than the root, such as the nodes of the stolon above.

They attach plants like ivy to host plants or trees and support other plants.

Purdue Turfgrass Program University of Wisconsin Master Gardeners Texas A&M University

Fibrous root system of violets Taproot System of a dandelion Adventitious roots of a

(Viola spp.) (Taxaracum officinale) strangler fig (Ficus spp.)

Figure 8: Root structure


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Reproductive Organs

The Bud

Buds are undeveloped shoots from which leaves or flowers can grow. A leaf bud is composed of a

short stem with embryonic leaves. A flower bud is composed of a short stem with embryonic flower

parts. Herbaceous perennials have naked buds with green, somewhat succulent, outer leaves.

Buds are named for their location on the plant. Terminal buds are located at the apex (tip) of a

stem. Lateral or axillary buds are located on the sides of a stem and usually arise where a leaf

meets a stem (at a leafaxil). In some instances, an axil contains more than one bud.

(c) 2002 Steven J. BaskaufThe Flower

Many landscape plants are grown for their attractive flowers. Plants have evolved with showy,

fragrant flowers to attract pollinators (insects and birds). Flowers contain the reproductive

organs of the plant. They can be used to identify and classify plants because flowers are the

plant part least influenced by environmental changes. Thus, knowledge of flowers and theirparts is essential for anyone interested in plant identification

There are many different kinds, shapes, and sizes of flowers, and we will look at them later in

the term. This is an introduction to the basic parts of the flower.


Lateral or axillary buds Terminal bud

Fi ure 9:
http://extension.oregonstate.edu/mg/botany/glossary.html#apexhttp://extension.oregonstate.edu/mg/botany/glossary.html#axilhttp://extension.oregonstate.edu/mg/botany/glossary.html#axilhttp://extension.oregonstate.edu/mg/botany/glossary.html#axilhttp://extension.oregonstate.edu/mg/botany/glossary.html#axilhttp://extension.oregonstate.edu/mg/botany/glossary.html#apex


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The picture above is a generic drawing of a complete flower. A complete flower contains all 4

floral structures: the sepals, petals, stamens, and pistils. These structures are arranged in

whorls around the flower stem. Sepals are the leaf-like structures that usually enclose other

flower parts. Petals are the whorl of floral parts that encircle the stamens. They are the

colored part of the flower. Stamens are the male flower part. It consists of a pollen sac, theanther, supported by a long filament. The pistil is the female part of the flower. It is shaped

somewhat like a bowling pin and is located at the center of the flower. It consists of a stigma,

located at the top and connected to the ovary by the style. The ovary contains ovules which

contain the eggs. If an egg is fertilized, the ovule develops into a seed.

A flower with a stamen, a pistil, sepals, and petals is a complete flower. If one or more of the

structures is missing the flower is called incomplete. The reproductive organs (stamen and

pistil) are the essential parts of the flower. If a flower contains both functional stamens and

pistils it is called a perfect flower. If either stamens or pistils are lacking the flower is calledimperfect. Pistillate (female) flowers possess one or more functional pistils, but lack stamens.

Staminate (male) flowers contain stamens, but no pistils. Imperfect flowers are further

classified as monoecious (plants have separate male and female flowers on the same plant) or

dioecious (species has separate male and female plants). Ginkgo trees (Ginkgo biloba) are

dioecious as is the Prairie willow (Salix humilis) pictured below.

Flowers may be borne on plants singly or in clusters called inflorescences. Showy flower

heads are often inflorescences. The type of inflorescence is determined by the arrangement

of the flowers and the position of the oldest and youngest blooms.

sepal

petal

stamenpistil


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Umbel Head Raceme

Figure 10: Inflorescences

The fruit

The ovaries contained in the flower mature along with other flower parts to form the fruit. The

function of the fruit is to protect the seeds which are the mature ovules. Most fruit has three

tissue types. The exocarp is the outer covering or skin. The endocarp is a boundary around theseeds that can be hard or papery. The mesocarp is the fleshy tissue of the fruit that is between

the exocarp and endocarp. Fruit structure can be used to classify plants. Simple fruits are the

most diverse category ranging from fleshy fruit such as apples and peaches and dry fruits and

nuts. There are many categories with in simple fruit. Aggregate fruit are clusters of tiny fruitlets

that develop from a single flower with many pistils. Blackberries and strawberries are

aggregate fruit. Multiple fruit develop from many flowers in a single inflorescence. Figs and

Receptacle

Ray floret

Disk floret

Youn est flower

Flower stalk

Oldest flower


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pineapples are multiple fruit.

Figure 9: Fruit classificationsCopyright Oregon State University.

Underground storage organs

Underground storage organs are specialized plant structures that contain reserves of

carbohydrates, nutrients, and water. Herbaceous plants that die back at the end of the growingseason and survive as fleshy underground storage organs are called geophytes. Geophytes

evolved specialized structures as a survival mechanism that allows them to live through adverse

climatic conditions (very hot or cold temperatures, drought) and maintain a perennial life cycle.

When environmental conditions are not favorable the above ground plant structure dies back

but the storage organ remains alive. We say that the plant is dormant at this stage. When

aerial growth is halted, the storage organ continues to change and sense its environment.

When conditions are favorable the plant emerges from dormancy and resumes its above

ground growth. The plant uses carbohydrates, nutrients, and water from the storage organ to

support growth until the plant can produce new carbohydrates through photosynthesis and

absorb nutrients and water with newly grown roots.

The term bulb is often used as a general term for all modified underground plant structures.

But, there are actually several types of storage organs. Each organ is defined by the plant part

from which it originated and by the tissue that is the primary storage tissue.


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True bulb: a compressed stem with storage leaf scales

Bulbs are highly compressed underground stems with numerous, overlapping storage leaves

(scales) attached. It is in the scales that most of the carbohydrates are stored. One or more

buds on the bulb sprout in the spring and produce an elongated stem, leaves, and flowers.

Roots grow from the base of the compressed stem (the basal plate). The above ground leavesproduce carbohydrates through photosynthesis. Some of the carbohydrates are transported to

the scales for storage. Offsets (new miniature bulbs) form at the base of some scales and

eventually split off from the parent bulb.

There are 2 types of bulbs; tunicate and non-tunicate. A tunicate bulb has a tight solid

structure with fleshy scales arranged in concentric layers and covered by a dry, papery

protective layer (the tunic). Onions, daffodils, tulips and hyacinth are tunicate bulbs. Non-

tunicate (or scaly) bulbs, such as lilies, have loose separate scales with no protective layer.

From The Physiology of Flower

Bulbs, 1993.

Tulip bulbtunicate bulb Lily bulbscaly or non-tunicate bulbCourtesy of the Chicago Botanic Garden UC Davis

Corm: a swollen stem base

A corm is the swollen underground base of a stem. It has nodes and internodes and is

enclosed in dry, scale-like leaves. The nodes appear as a series of lines around the corm.

Carbohydrates are stored in the stem structure, not in the leaf scales as in bulbs. Buds sprout

from the top of the corm and produce upright stems which bear leaves and flowers. Roots

extend from the basal plate at the bottom of the stem. Some corms have contractile roots that

shrink when they lose water, pulling the corm further underground and holding the


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aboveground plant tightly against the soil. This may help protect the corm from cold injury.

Corms only last 1 season. After bloom, one or more new corms develop at the top of the old

corm which disintegrates.

From The Physiology of Flower Bulbs, 1993.

Gladiolus corm

UC Davis

Tuber: swollen stem tissue

An underground tuber consists of swollen stem tissue with nodes and internodes. Like with

corms, the stem serves as the primary storage tissue. Unlike the corm, there is no basal plate

on a tuber. Shoot arise from buds (eyes) all around surface of the tuber. Roots grow from the

lower part of the emerging shoots. The lower portion of the shoot enlarges to form a new

fleshy tuber.


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From The Physiology of Flower Bulbs, 1993. Potato tuber sproutingPhoto by Peggy Greb. ARS USDA

Rhizome: horizontal stem

A rhizome is a horizontally growing stem just at or slightly below the soil surface. The stem

structure acts as a storage organ. Some rhizomes are thick and fleshy (Iris) and others areslender (bentgrass). Because they are stems, rhizomes have nodes and internodes. Leaves,

flower stalks, and roots develop from the nodes.


Ginger rhizome

UC Davis

Enlarged hypocotyl: enlarged stem

The hypocotyl of a seedling is the portion of the stem below the cotyledon (the first leaves that

emerge when a seed germinates) and above the roots. In some plants, the hypocotyl enlarges,

becoming a fleshy storage site as the plant develops. Tuberous begonias are not actually

tubers; they have enlarged hypocotyls.

Eye


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Cyclamen enlarged hypocotyl

2000-2008 Touchofnature.com.

Tuberous Root: root tissue

A tuberous root is, surprise, root tissue not stem tissue like the previous underground organs.

The tuberous root is an enlarged, fleshy secondary root that serves as storage tissue .

Tuberous roots have no nodes or internodes or eyes on their surface. Shoots emerge from the

top (crown). Fibrous roots grow from the thickened root during the growing season and absorb

water and minerals. Tuberous roots grow in groups with the swollen roots extending out from

a central point.


Dahlia tuberous roots

UC Davis

The diagrams are from De Hertogh, A.A. and M. Le Nard. 1993. The Physiology of FlowerBulbs. Elsevier Scientific Publisher. Amsterdam, The Netherlands.
http://www.hort.cornell.edu/department/faculty/wmiller/bulb/referenc.html#DeHhttp://www.touchofnature.com/copyright.htmhttp://www.hort.cornell.edu/department/faculty/wmiller/bulb/referenc.html#DeHhttp://www.hort.cornell.edu/department/faculty/wmiller/bulb/referenc.html#DeHhttp://www.touchofnature.com/copyright.htmhttp://www.hort.cornell.edu/department/faculty/wmiller/bulb/referenc.html#DeH

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Plant Anatomy Week 1