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EXTENSION
EC1259

Garden Terms:
Vegetative plant morphology —
Black/PMS 186
Stems, leaves, and rootsEXTENSION
Anne M. Streich, Extension Horticulture Educator

Stems vascular systems are arranged in continuous rings

around the inside of the stem (Figure 1).
Stems are used to carry water and nutrients throughout Xylem tissues are water and nutrient conducting
Black
EXTENSION
the plant. They also provide the above-ground channels in plants. In woody plants, the xylem makes
framework for the plant. annual rings. These rings may provide information
about the plant’s age and the environmental
conditions it has experienced. Narrow xylem rings
Internal Stem Characteristics may indicate drought conditions, while wider rings
may indicate more desirable growing conditions.
Vascular plant systems contain four major internal
parts: the xylem, phloem, cambium, and pith. Monocot Phloem tissues are food-conducting channels
vascular systems are arranged in paired bundles. These in plants. These tissues transport sugars, from
bundles are dispersed throughout the stem. Dicot photosynthesis, throughout the plant. In woody

a b

Figure 1. Flowering plants (angiosperms) are classified as either monocotyledons (monocots) or dicotyledons (dicots). Along with other
morphological differences, the vascular system of each is significantly different. The vascular systems of monocots are arranged
in paired bundles (a), while the vascular systems of dicots are arranged in continuous rings (b).

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 a b
Figure 2. Leaf scars vary in size and shape and are valuable identification characteristics during the winter months. Leaf scars also may be
helpful in distinguishing plants of the same genus, such as white ash (a) with a horseshoe or “C” shaped leaf scar and green ash
(b) with a flat or “D” shaped leaf scar.

plants, the phloem ring is near the bark and is a Buds are the stem’s primary growing points. They can
component of the bark in mature stems. be either leaf buds (vegetative) or floral (reproductive)
buds. Leaf buds are often less plump and more pointed
Cambium is meristematic tissue, which is a site than flower buds. The buds of trees and shrubs of the
of cell division and active growth. It is a single temperate zone typically develop a protective outer
celled layer located between the xylem and phloem. layer of small, leathery bud scales. Annual plants and
It produces both xylem and phloem tissue. Cell herbaceous perennials have naked buds in which the
division in the cambium layer is responsible for the outer scales are green and somewhat succulent. Buds are
annual increased diameter of healthy growing woody commonly used in plant identification.
plant stems.
Terminal buds are located at the tip of a stem (Figure
Pith refers to the center portion of a stem. Piths 3). When terminal buds are removed (called pinching
may be hollow, solid, chambered or colored. These when done on herbaceous plants), plants will develop
characteristics can be helpful in plant identification. a denser and typically wider growth habit.

Lateral buds are borne on the sides of the stem.

External Stem Characteristics
Adventitious buds arise at sites other than in the
Leaf and bundle sheath scars are marks left on the stem terminal or lateral position. Adventitious buds may
where a leaf was previously attached (Figure 2). These develop from the internode of the stem, at the edge
scars vary in size, shape and color, and are often used in of a leaf blade, from callus tissue at the cut end of a
plant identification when plants are dormant. stem or root, or laterally from the roots of plants.

a b c
Figure 3. Terminal buds may be single (a), as seen in many plants; double (b), commonly seen in lilac; or clustered (c), commonly seen in
oak.

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 a b

Figure 4. Some plants have distinct lenticels that are valuable for identification, such as callery pear (a), with distinct horizontal white
lines; and forsythia (b), with raised bumps.

Terminal bud scars are marks left around the entire Stem Types
stem at the place where the previous year’s growth ends.
Measuring the distance between terminal bud scars is an Shoot refers to the first-year growth on a woody or
effective method in determining annual growth rates. herbaceous plant. It has leaves present.
Lenticels are pores on stems and bark that allow for gas Twig is a stem that is 1 year old or less and has no leaves.
exchange. Some plants have distinct lenticels that are It is still in the winter dormant stage.
valuable for identification (Figure 4).
Branch is a stem that is more than 1 year old and
Bark is the protective outer layer of the stem that typically has lateral stems.
develops with age. Bark is a valued identification
characteristic due to its year-round availability. Bark Trunk is the main stem of a woody plant. Most large
color and texture often vary with plant maturity but can shade trees have a single trunk, but many smaller
be distinct for many plants (Figure 5). ornamental trees, such as birch, serviceberry, and
Japanese tree lilac, typically have a multi-trunk habit.
Node is an area of the stem where leaves and lateral buds
are located. Nodes are areas of great cellular activity and Water sprouts are adventitious shoots that arise from
growth. branches. They grow rapidly and typically have upright
growth orientation and a weak structure and attachment
Internode is the area of stem located between two to the branch.
nodes. Internode lengths may depend on many factors,
including fertility levels, environmental conditions, and Suckers are adventitious shoots that arise from the
plant competition. base of the plant. They grow rapidly and typically have

a b
Figure 5. Bark color and texture often vary with plant maturity but can be distinct for many plants, including white oak (a), and scotch
pine (b). White oak bark is light gray with narrow ridges. Scotch pine is orangish brown with a thin papery appearance. Both
trees have bark that is distinctive from a distance.

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 Figure 6. Perennial weeds with creeping stems (either rhizomes or stolons), such as white
clover, can be difficult to control because the extent of spread can be difficult to
determine. When herbicide applications are used, they should be applied slightly
beyond the visual edge of the weed spread.

upright growth orientation. Many plants in the Rosaceae Tuberous stems are short, flat, and enlarged stems found
family sucker. Other plants may sucker as an indication underground. Examples include tuberous begonia and
of plant stress. cyclamen.
Canes are stems that have relatively large piths and usually Corm is a compressed stem with reduced scaly leaves. An
live only one or two years. Examples of plants with canes example is gladiolus.
include roses, grapes, blackberries, and raspberries.
Bulb is a compressed underground stem surrounded by
fleshy scales (leaves) that attach at the base. Examples
Modified Stems include tulip, lily, daffodil, and onion.

Crown is a region of compressed stem tissue from which Spur is a short, stubby, side stem that arises from the
new shoots are produced, generally found near the main stem. They are common on fruit trees, such as
surface of the soil. pears and apples. Spurs typically contain the flower buds
and serve as the attachment between the fruit stem and
Stolon (runner) is a specialized stem that grows branch.
horizontally above the soil surface and forms a new plant
at one or more of its nodes. Examples include strawberry, Thorns are modified, sharp-pointed stems that occur
buffalograss, and ajuga (Figure 6). in the leaf axil. Examples include buckthorn and
honeylocust.
Rhizome is a specialized stem that grows horizontally
below the soil surface and acts as a storage organ and
means of propagation in some plants. Some rhizomes Leaves
are compressed and fleshy, such as iris; others are slender
with elongated internodes such as Kentucky bluegrass. Leaves are the principle location for photosynthesis,
transpiration, and respiration in plants.
Tuber is an enlarged portion of an underground stem
that stores food for the plant. An example is potato.

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 Cuticle
Epidermis
Palisade layer

Guard cell Stoma Epidermis

Spongy parenchyma
layer

Stoma
Figure 7. Stomata are microscopic natural openings in the leaf that allow for gas exchange, including water vapor, carbon dioxide, and
oxygen. The opening and closing of stomata is controlled by guard cells.

Internal Leaf Characteristics Guard cells protect the interior of the leaf and regulate
the passage of water, oxygen, and carbon dioxide through
Epidermis refers to the top and bottom layers of cells the stomata. The opening and closing of guard cells are
on a leaf. The primary function of the epidermis is to determined by environmental conditions.
protect leaf tissue.
Mesophyll is interior leaf tissue that may be divided
Cuticle is the outer layer of the epidermis. It produces into a dense upper layer of cells called the palisade and
a waxy layer called cutin. Cutin protects leaves from a lower layer of loosely grouped cells called the spongy
dehydration and prevents penetration of some diseases parenchyma. The cells in these two layers contain
from penetrating. Cuticle thickness is a direct response to chloroplasts, which is the actual site of photosynthesis.
sunlight, increasing in proportion to light intensity. For
this reason, plants grown in the shade should be moved
into full sunlight gradually. This will allow the cuticle
External Leaf Characteristics
layer to thicken to protect the leaves from the shock of
Blade refers to the flattened, expanded thin structure
rapid water loss or sunscald.
on either side of the leaf midrib. Blades are usually
Stomata are microscopic natural openings in the leaf the largest and most conspicuous part of the leaf. This
that allow for gas exchange, including water vapor, surface is used to absorb light energy to be used in
carbon dioxide, and oxygen (Figure 7). photosynthesis (Figure 8).

Blade

Midrib Petiole

Leaf Base
Stipule

Leaf Margin

Leaf Apex
Figure 8. External leaf characteristics, such as those found on firethorn, Pyracantha
coccinea, are valuable keys to plant identification.

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 a b

c d

Figure 9. Plants exhibit different types of venation, including pinnate (a), palmate (b), dichotomous (c), and parallel (d).

Petiole is the stem-like appendage that supports the Veins are vascular bundles (which contain xylem and
leaf away from the stem. It may vary in length or may phloem) that extend from the stem through the petiole
be lacking entirely in some cases. Cottonwood tree and spread out in the blade. Venation refers to the
leaves have very long petioles that allow the leaves to patterns in which the veins are distributed in the blade
characteristically flutter in a gentle breeze; elm leaf (Figure 9).
petioles are typically measured in fractions of an inch.
Net-veined (reticulate-veined) leaves have veins
Stipules are leaf-like appendages at the base of the leaf. which branch from the main rib or ribs and
then subdivide into finer veinlets that unite in a
Shape refers to the overall form of the leaf. Other leaf
complicated network. This system of enmeshed
characteristics, such as the shape of the leaf apex, base,
veins gives the leaf more resistance to tearing than
and margin, are useful in plant identification.
parallel-veined leaves. Net-veined leaves occur on
plants that are part of the dicotyledon group.

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 Opposite Sub-Opposite Alternate Whorled
Figure 10. Leaf arrangement is one of the primary characteristics used to help separate plants in vegetative plant keys. Most plants have
alternate or opposite leaf arrangement, but sub-opposite, whorled and rosette arrangements are also observed on plants.

Palmate veined leaves have principle veins Alternate arranged leaves are positioned in alternate
extending outward from one point, usually steps along the stem with only one leaf at each node.
from near the base of the leaf blade. This type of Examples of plants with this type of arranagement
venation occurs in grape and maple leaves. include oak, elm, linden, and cottonwood.

Pinnate veined leaves have veins extending Whorled leaves are arranged in a cluster pattern of three
laterally from the midrib to the edge. This is or more leaves at a single node. An example of a plant
the most common type of venation among with this type of arrangement is catalpa.
net-veined plants. Pinnate venation is found in
common plants such as apple, oak and elm. Rosette leaves are arranged in a cluster at the base
of the stem. Examples of plants with this type of leaf
Dichotomous veined leaves have veins arranged in a arrangement include dandelion and many biennial
unique “Y” shaped formation. This type of venation plants during the first year of growth.
is only found in ginkgo.

Parallel veined leaves have numerous veins that run Broadleaf Leaf Types
essentially parallel to each other and are connected
laterally by minute straight veinlets. One of the most Simple leaves are those in which the leaf blade is a single
common types of parallel-veining is found in plants continuous unit (Figure 11).
of the grass family (Poaceae), where the veins run
from the base to the apex of the leaf. Another type Compound leaves are divided and are composed of
of parallel venation is found in as banana, where the several separate leaflets. In determining whether a leaf is
parallel veins run laterally from the midrib. Parallel- simple or compound, locate where the petiole attaches to
veined leaves occur on plants that are part of the the stem (adjacent to a bud). Leaflets do not have buds
monocotyledon group. associated with them, so all leaf parts, including and
beyond the attached petiole, comprise a single leaf.

Leaf Arrangement Pinnately compound leaves have leaflets arranged

on both sides of the rachis (central leaf stem). An
Opposite arranged leaves are positioned across the stem example is white ash.
from one another, two leaves at each node. Examples of
Bipinnately compound leaves have a double set of
plants with this type of arrangement include maple, ash,
leaflets. An example is Kentucky coffeetree.
dogwood, viburnum, and buckeye (Figure 10).
Palmately compound leaves have leaflets radiating
Sub-opposite leaves reflect an opposite pattern with
from a central point. An example is Ohio buckeye.
a slight offset. An example of a plant with this type of
arrangement is European buckthorn.

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 Leaflet
Leaf
Leaf

Bud
a Bud b
Figure 11. Simple (a) and compound (b) leaves can be differentiated by bud location. Leaflets of a compound leaf do not possess buds.

Needle-like Leaf Types Internal Root Characteristics

Awl-shaped leaves are sharp to the touch. Many junipers Meristematic zone is an area of cell division and growth.
have awl-shaped leaves.
Root cap is the outermost tip of the root and
Needle-like leaves can be borne singly (firs, spruces) or consists of cells that are sloughed off as the root
in clusters/fasciles (pines). grows through the soil. The root cap protects the
root meristem, located directly behind the root cap.
Scale-like leaves have overlapping leaves that are soft The root meristem is an area of cell division.
to the touch. Examples include arborvitae and many
junipers. Zone of elongation is located behind the meristematic
zone. In this area, cells increase in size through food and
water absorption. These cells, by increasing in size, push
Modified Leaves the root through the soil.

Adhesive discs are modified leaves used for attaching to Zone of maturation is the location where cells undergo
surfaces. Boston ivy clings to walls with adhesive discs. changes to become specific tissues.

Bracts are specialized leaves which are often brightly Epidermis cells compose the outer layer of the root.
colored. The showy structures on flowering dogwood Root hairs are an extension of epidermal cells in the
and poinsettias are bracts, not petals. root. These tiny, hair-like structures are responsible
for the majority of the nutrient and water
Spines are sharp-pointed modified leaves. They are absorption from the soil. Root hairs are delicate and
usually located at the base of a leaf. Examples include can be easily damaged.
cactus and barberry.
Vascular tissue is located in the center of the root.
Tendrils are modified leaves that assist in supporting the These tissues conduct food and water throughout
stem by wrapping around small diameter objects and the plant.
structures. Woodbine and porcelain vine both produce
tendrils for attaching to vertical structures.
Root Types
Roots Tap roots are primary roots that elongate mainly
downward into the soil and become the central and most
Roots are used to provide support for the stem, to absorb important feature of the root system. Examples include
water and nutrients for plant growth, and to store food walnut, oak, and carrot. Plants that produce tap roots
(Figure 12). will also typically develop some fibrous roots to allow
oxygen, water, and nutrient uptake near the soil surface.

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 Zone of Maturation

Root Hairs

Root Tip

Zone of Elongation
Rootcap Meristematic Zone

Figure 12. Roots are important for the absorption of water and nutrients for plant growth. Damage to roots, especially the root hairs,
during planting or transplanting can hinder plant growth and development.

Fibrous root systems have numerous branched roots. Aerial roots arise from above-ground stem tissue.
The greatest concentration of fibrous roots occurs in the
top 18 inches of soil, but significant numbers of lateral Tuberous roots are underground storage organs. They
roots may grow downward from these roots to provide are often confused with tubers, but do not contain stems,
an effective absorption system in deeper locations. so they are classified as roots. Examples include dahlia
Examples include turfgrasses, most perennial and annual and sweet potato.
flowers, and many trees and shrubs.

Adventitious roots arise from locations where root

growth normally does not occur.

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