This content provides a comprehensive overview of plant morphology and anatomy, detailing the structures, functions, and life cycle stages of plants, which is crucial for understanding and classifying them.
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Plant morphology is the description of the physical form and external structure of plants
while plant anatomy is the study of the internal structure of plants. Look at this tomato plant, it is made up of
roots, stems, leaves, flowers, and fruits. If you dig in deeper, you notice that the
root is a taproot system, that the leaves are compound leaves in a alternate attachment
to the stem, the flower parts are in multiples of 5s, and the fruit is a fleshy berry. I’m
Dr. DeBusk and in this video, you will dive into the terms for plant anatomy and morphology,
so that you may understand plants more and be able to classify them. You also learn what
I meant when I described that tomato plant. The plant’s life cycle has three phases
with varying characteristics. In the initial period of growth, the apical meristem, which
is the primary growing point of the stem, will not typically respond to internal or
external conditions to initiate flowers. The juvenile phase of development exhibits exponential
increases in size and the inability to shift from vegetative to reproductive maturity leading
to the formation of flowers. In addition, juvenile plants have specific morphological
and physiological traits. Hedera helix, or ivy, in the immature stage has five lobes,
whereas in the mature stage it has none. The ivy commonly seen around campuses is mostly
immature; it is actually fairly hard to find plants in the mature stage. Young growth in
Juniperus virginiana, Eastern red cedar, has thorns, whereas older growth does not. Examples
of physiological traits during the juvenile stage include vigorous plant growth, disease
resistance, and a greater ability to regenerate roots and shoots. The reproductive or mature
phase refers to qualitative changes that allow the plant or organ to express its full reproductive
potential. Both genetic and environmental conditions determine when plants enter this
phase. Senescence phase involves internally controlled deteriorative changes, which are
natural causes of death. Changes that occur during senescence include the following: decreases
in chlorophyll, protein, DNA and RNA, and photosynthesis; and changes in plant hormones
– some increase while some decrease. When the senescence phase is complete, leaf abscission
occurs. The leaves, stems, and roots make up the primary
vegetative structures of the plant. They take part in growth processes that are essential
to the plant’s survival. The main function of a leaf is to manufacture food for the plant
during photosynthesis. Photosynthesis refers to a series of chemical reactions in which
carbon dioxide and water are converted in the presence of light to carbohydrates (sugar)
and oxygen. Both light and chlorophyll are essential to photosynthesis. Carbon dioxide
and other gases enter and exit the leaf through tiny pores in the leaf’s surface called
stomata. Another important function carried out by the leaf is transpiration, which is
the loss of water from the leaf in the form of water vapor. Respiration is another important
function carried out by the leaf; this process uses sugars made during photosynthesis and
breaks them down into simpler molecules (such as water and carbon dioxide) that are used
as energy for plant growth and development. Leaves consist of several basic parts that
help identify them. The major parts of a simple dicot leaf are listed here. If you start at
the stem, the leaf stem or stalk that attaches the leaf is the petiole. The blade is the
flat thin part of the leaf. The midrib is the largest vein located in the middle of
the leaf. Veins are used to transport water and nutrients throughout the plant. The different
leaf venation patterns found in plants can be parallel, pinnate, palmate. Monocot plants
have only parallel venation. The leaf margin is the outer edge of the leaf blade, which
can be lobed, smooth, toothed, or various combinations of the three. The leaf apex is
the tip of the leaf blade, which can be pointed, rounded, or a variety of other shapes. The
leaf base is the bottom of the leaf blade, which can be rounded, pointed, or a variety
of other shapes. A stipule is a small leaflike appendage to a leaf, typically borne in pairs
at the base of the leaf stalk. Various leaf coverings include hairy versus not hairy,
waxy versus not waxy, and others. The simple leaf consists of one blade per
petiole, such as found on an oak leaf. The compound leaf has two or more leaflets, such
as found on a potato leaf. The main difference between a leaf and a leaflet is the position
of the axillary bud, which is located at the base of the entire leaf; leaflets do not have
axillary buds. Differences in how leaves are attached to stems are commonly used as a means
of plant identification. Leaves are attached to stems in three major patterns. The opposite
pattern occurs when two leaves are directly across from each other, or two leaves per
node. The alternate pattern occurs when leaves are staggered along the length of the stem,
or one leaf per node. The whorled pattern occurs when three or more leaves are attached
per node. Modified leaves are commonly mistaken for
other structures such as flowers or stems. To illustrate this point, these are some examples
of modified leaves. Bracts are leaves located just below the flower, for example, the poinsettia
and dogwood. Tendrils are appendages produced by certain vines that wrap around a support
and allow them to climb, for example, the grape.
Stems can be used to identify plants with some practice. The stem has several important
functions. Stems are used to support leaves, flowers, and fruits. Stems contain important
transport systems, including the xylem for transporting water and minerals, and the phloem
for transporting manufactured food. Stems can be used to manufacture food, but to a
lesser extent than the leaves. Stems can act as a storage organ for food; an example of
this is the Irish potato. The basic parts of the stem are described
here. The terminal bud is positioned at the tip of the stem and contains an undeveloped
leaf, stem, flower, or mixture of them all. The bud scale is a tiny leaf-like structure
that covers the bud and protects it. The terminal bud-scale scar is left when the terminal bud
begins growth in the spring; it represents one year’s growth. The axillary bud is located
along the side of the stem below the terminal bud. The node is the point along the length
of the stem where leaves or stems are attached. The internodal region is located between the
nodes. The leaf scar is left when the leaf drops. The lenticels are tiny pores located
in the stem and are used for gas exchange; an example of a tree with conspicuous lenticels
is the cherry tree. Within the stem, the water, nutrients, and
food made during photosynthesis are transported throughout the plant and stored for later
use. The internal anatomies of a monocot (has one cotyledon and parallel leaf venation)
and dicot stem (has two cotyledons and reticulate leaf venation) are shown on the slide. A key
feature is that monocots have vascular bundles that are scattered and dicots have vascular
bundles in a ring. The following are key anatomical features found in stems. The outer layer of
plant parts is the epidermis, just like our skin is our epidermis. The primary tissue
of the stem or root is the cortex, which is located between the epidermis and vascular
region. Think of this as the filler tissue. The cambium is the area where new plant cells
are formed – either xylem or phloem during secondary growth. When grafting, the cambium
layers must match for the graft union to be successful. The cambium is only found only
in woody plants. The xylem is composed of tiny tubes that transport water and nutrients
up from the roots to other parts of the plant. The annual rings in a tree are made up of
xylem. The phloem is composed of tiny tubes that transport manufactured food and carbohydrates
from the leaves down to other parts of the plant, such as the roots and shoots. The pith
is located in the center portion of the stem where food and moisture are stored.
In addition to standard stems, there are also modified stems used for storage of reserves
and for reproduction. An aboveground horizontal stem with long and thin internodes is a stolon,
such as in strawberry runners. A belowground horizontal stem is a rhizomes, such as ginger
root or turmeric. A tuber is an underground rounded swelling of a stem such as Irish potatoes.
Corms are vertical, thick stems with thin, papery leaves, like gladiolus. Bulbs are short
shoots with thick, fleshy leaves like onions and tulips.
The major function of the root is to absorb water and nutrients to sustain plant life.
In addition, roots act as storage organs for carbohydrates and provide anchor and support
for the top portion of the plant. The first structure to emerge from a germinating seed
is the root. The key parts of the root are described here. The primary root is the main
root that first emerges from the seed. Starting from the tip of the primary roots, there is
a the root cap, just behind the root cap is the area of cell division, followed by the
area of cell elongation, and then the area of maturation or cell differentiation. The
secondary root arises from the primary root. Root hairs are single cells that absorb the
greatest amount of water and minerals. Improper handling during transplanting can cause the
loss of many root hairs, which decreases the plant’s water uptake and results in transplant
shock. The root cap is located at the tip of the root and consists of several layers
of cells that protect the root as it grows through the soil.
There are two major classes of root systems. The taproot system has a primary root that
grows down from the stem with only a few secondary roots; both carrots and dandelions are examples.
This is common for dicots. The fibrous root system has a large number of small primary
and secondary roots; potato plants and grasses are examples. This root system is common for
monocots. Modified roots serve as a reserve food-storage system; an example of a modified
root is a sweet potato. Be careful not to confuse the modified-root sweet potato with
the modified-stem Irish potato. The reproductive parts of the plant are the
flowers, which are pollinated and fertilized to produce the fruits. The main function of
flowers is to attract pollinators and to produce fruit and seed. Flowers come in a variety
of sizes, shapes, and colors to achieve their main function. In addition to their main function,
flowers are commonly used for plant identification and produced commercially for their beauty
and fragrance. A typical flower consists of four major parts. The sepals are green, leaf-like
structures located beneath the petals. The calyx is the term used to describe all the
sepals on one flower. The calyx is used for protection. For example, some plants have
calyx that contain spines, which deter animals from feeding on them. The petals are the brightly
colored portions of the flower that are used to attract pollinators. The stamens are the
male reproductive part of the flower. The stamen consists of a filament that supports
the anther, which produces the male sex cells (pollen). The pistils are the female reproductive
part of the flower. The pistil consists of the stigma, which is the sticky surface for
collecting pollen; the style, which is the tube that connects the stigma and ovary; and
the ovary, which contains ovules or eggs. Monocots typically have flower parts in multiples
of 3 while dicots have their flower parts in multiples of 4s and 5s.
Flowers can be broken down into four different classes. The complete flower contains all
four major flower parts: sepals, petals, stamens, and pistils. The incomplete flower lacks one
or more of the major flower parts. In the photo of the American elm, the sepals and
petals are lacking. Since these plants are pollinated through wind, this allows the wind
to pick up the pollen easier and for it to blow onto the pistil. The perfect flower contains
both stamens and pistils. The imperfect flower lacks either stamens or pistils; an example
of a plant containing this type of flower is corn.
Fruits are formed after the flower has been pollinated and fertilized. The definition
of a fruit is a mature ovary of a flowering plant. There are two types of fruits. The
fleshy fruit, such as a tomato, has soft fleshy material with or without seeds enclosed. The
dry fruit, such as a sunflower, has seeds enclosed in a hard fruit wall. Isn’t it
wild that something like beans or corn is considered a fruit? From the botanical definition,
a fruit simply comes from the ovary of a plant while a vegetable comes from the roots, stems,
leaves, or flowers of a plants like cauliflower or lettuce. By this definition, a tomato is
mostly definitely, a fruit. The informal definition of a fruit is something that is sweet.
A seed is the mature fertilized egg that is contained in the fruit. Seeds can be dispersed
by the wind like dandelions, stuck to the fur of animals, or spread in other ways. Dicots
store their reserved food in cotyledons, whereas monocots store their food in the endosperm.
The germination process is a series of events whereby the seed embryo goes from a dormant
state to an actively growing state. For seed germination to occur, the following criteria
must be met. The seed must be viable, which means that the embryo is alive and capable
of germination. The seed must be exposed to appropriate environmental conditions. Primary
dormancy must be overcome in the seed. Three stages of seedling germination are as
follows. First is imbibition of water which is the active uptake of water by the seed.
After the seed is hydrated, preexisting enzymes are immediately available for breaking down
storage reserves, and new enzymes are produced for the breakdown of additional reserves.
Lastly, preexisting and newly formed enzymes break down food reserves, which are used for
the germination process. The first visible sign of seed germination and growth is the
emergence of the radicle followed by growth of the seedling. The following are two common
forms of seed germination. Epigeous seed germination where the hypocotyl elongates and brings the
cotyledons above ground like in cherries. Hypogeous seed germination where the epicotyl
emerges and the cotyledons remain below the soil surface, such as in corn.
You heard various differences between monocots and dicots. You should be able to identify
these differences. Here is a summary. Monocots have one cotyledon, leaf veins that are parallel,
vascular bundles in their stem are scattered, fibrous root system, and flower parts in multiples
of three. Dicots have two cotyledons, veins that are netlike or reticulate, vascular bundles
are usually arranged in a ring, a taproot system, and flower parts in multiples of four
or five. In conclusion, knowledge of basic plant anatomy, including vegetative (leaves,
stems, and roots) and reproductive (flowers and fruits) plant parts, together with understanding
the plant’s life cycle is important in plant classification, as well as in maximizing the
plant’s potential uses.
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