Plant Components and Descriptions
The purpose of this exercise is to expose students to common terms and anatomical parts
used to identify plants; in turn, species are placed in established taxonomic groups in
herbaria or planted in planned landscapes. Because space is limited in botanical text,
students of plants have become accustom to using a few morphological terms to describe
plants in detail.
Root Systems
Root systems are rarely used in the identification or classification of plants. Yet,
horticulturists often develop watering practices based on root type, age, size, and
location.
Roots develop from the seed as a primary or first structure, and then others emerge as
secondary types, also called adventitious roots, from other growth areas. The following
types are often recognized for identification purposes:
Fibrous root – is a very thin, long root system often without a primary root, as in the
Kentucky Bluegrass.
Tap root – is a medium sized root; may have several secondary roots, often storing water
and food, as in the Hybrid Tea Rose.
Succulent or tuberous root – is a thick, fleshy root providing storage areas for water and
food, as in the Tuberous Begonia.
Adventitious root – is a root system produced either at the original root site or somewhere
else on the plant, as in the Corn plant.
Aerial root – is a root system produced for the purpose of holding climbing plants such as
epiphytes to another plant or object, as in the Orchid, Bromeliad, and Philodendron.
Mycorrhizae - is a symbiotic association of a fungus with the roots of certain plants, as
in the Conifer, Orchid, and Beech.
Stem Systems
The stems show morphological a range of shapes, sizes, longevity, location, and direction
of growth. Herbs, vines, shrubs, and trees show differences in stem size, longevity as
well as habit. The following are terms often used to describe stem components and
systems:
Bud – is an immature, compressed shoot covered by several modified leaves or scales.
Buds are located at the top (apical) or on the side (lateral) of a stem.
Node – is a place on the stem that may produce new leaves or stems.
Epidermis – is a thin, often green layer, of skin that protects the stem from dehydration,
diseases and pests.
Peridermis – is often a thick layer of bark that protects the stem from dehydration,
diseases, pests, and fire.
Cortex – is the bulky tissue in the center of a stem that may store water and food. In the
stem, parenchyma cells provide areas for storage, while at the same time vascular tissue
conduct water from the roots to the leaves or sap from the leaves to the stem and roots.
Modified Stem- is one of the many stem structures produced above or underground for
propagation as well as food and water storage. Inside some of the stems, young shoots
rest, which when stimulated by environmental factors, will begin to grow. Other stems
without young shoot produce fleshy stems to survive long periods of drought and aridity.
Common types and examples of modified stems include:
Bulb – is an underground stem that produces fleshy scales and young shoot
attached to a basal plate and adventitious roots, as in the tulip.
Corm – is an underground stem that produces a woody core and young shoot
attached to a basal plate and adventitious roots, as in a gladiolus.
Tuber - is an underground fleshy stem that serves as a storage structure for food
and propagation, as in the Russet Potato.
Rhizome – is an underground fleshy stem, often growing horizontally and
producing new shoots at their tips, as in the Dutch iris.
Stolon – is an above ground stem, producing roots at their nodes as well as new
plantlets while still connected to the parent plant, as in the strawberry.
Caulescent – is a stem that produces buds, leaves, and flowers at the nodes.
Growth Pattern – is the shape in which a plant grows, which may include the degree of
woodiness, mature height, spread, and number of basal stems.
Herbaceous – is a plant that produces stems containing very little woody tissue; skin
often green, but in some perennial species a brown bark layer is produced.
Shrub or fruticose – is a woody perennial producing sets of basal stems reaching a mature
height of 1 to 15 feet.
Vine – is a creeping, multi-stemmed plant commonly used as a ground cover or wall
cover.
Tree or arborescent – is a woody perennial, usually producing one trunk and reaching a
mature height from 15 to over 300 feet.
Life History
Life history is the sequence of events that a plant shows during its life. The common
terms used include the following:
Annual – is a plant that lives for one season or year providing vegetative growth and
reproduction, as in a Marigold.
Biennial – is a plant that lives for two years, producing only vegetative growth the first
year and vegetative and reproductive growth the second year. Fox Glove is classified as
a biennial.
Perennial – is a plant that lives for many years; shows juvenile, transitional, and adult
stage of growth, as in the oak and pine trees.
Deciduous – is a behavior in which leaves are shed at the end of a growing season, often
before winter.
Evergreen – is a behavior in which leaves persist for many seasons; some leaves may be
shed, but not all.
Leaf Systems
Leaves produce the food for the whole plant; they show different shapes to capture
sunlight to make sugars; some stems partially or complete release (deciduous) leaves
sometime during the year, while others keep most or all (evergreen) of the leaf system
throughout the year.
The components of a leaf are as follows:
Blade – is usually a flat, expanded portion of a leaf.
Petiole – is a leaf stalk that connects the blade to the stem and transports materials to and
from the blade.
Stipule – is small, paired appendages attached to the base of the petiole.
Axillary bud – is a leaf bud growing at the base of the petiole next to the stem.
Node – is a place where the petiole is attached to the stem.
Internode – is the area between adjacent nodes.
* Look for the stipules at the base of the petiole and an axillary bud above the petiole.
Leaf Arrangements
There are three four patterns of leaf arrangement on stems.
Alternate – is one leaf per node.
Opposite – is two leaves per node.
Whorled – is three or more leaves per node.
Fascicled – are leaves grouped in small, tight bundles, as in pine needles.
Leaf Composition
Leaf form and shape range from a complete blade to those that produce multiple divisions
of a blade. The classification of leaves is as follows:
Simple – is a blade undivided.
Leaflet – is a blade divided into featherlike (pinnate) or digit (palmate) patterns.
Compound – is a blade divided one or two into smaller sections.
Once pinnately compound – is a series of leaflets arranged on either side of an elongated
axis, or rachis.
Twice pinnately compound – is a series of two or more leaflets divided twice; first
division is the blade into two or more leaflets and the second division is the leaflets into
two or more smaller sections or pinnae.
Palmately compound – is dividing a blade into leaflets emerging from one point at the
base of the leaf.
Leaf Venation
Vascular tissue of leaves makes up the patterns of veins from the base to the tip of the
blade. There are four vein patterns is as follows:
Pinnate – is a vein pattern with a main midvein and secondary veins arising from it at
intervals; found in dicot leaves that produce a highly branched network throughout the
blade.
Palmate – is a vein pattern with several main veins all emerging from one point at the
base of the leaf; dicots also produce this type of venation.
Parallel – is a vein pattern with all of the main veins running side by side throughout a
leaf.
Dichotomous - is a vein pattern in which each vein divides again and again.
Leaf Margin
The edge of the leaf blade is its margin, which may show great diversity by producing
appendages that extend beyond the blade, or by developing shallow or deep indentations
into the blade. The margin terms are as follows:
Entire – is a margin that does not produce either appendages or lobes.
Pinnately lobed – is a blade with the lobes arising along the length of the mid-line of the
leaf.
Palmately lobed – is a blade with the lobes all arising from one point at the base of the
leaf.
Ciliate – is a blade with hairs on the margin forming a fringe.
Serrate – is a blade with sawtooth appendages on the margin.
Doubly Serrate – is a blade with small sawtooth appendages on the margin.
Dentate – is a blade with teeth that point out.
Undulate – is a blade with wavy or a serpentine pattern on the margin.
Revolute – is a blade turned under.
Crisped – is a blade curled tightly
Leaf Shapes
The general outline of the blade, or all of the leaflets of a compound leaf, constitutes the
shape of the leaf. Usually the shape is described as including only the blade, omitting the
petiole. The shape of a compound leaf is determined by drawing an imaginary line round
all projected parts, ignoring the indentations and the areas between leaflets. Common
terms used include:
Ovate – is an egg-shaped blade with a larger base than at the tip.
Elliptic – is a football shaped blade, which tapers from the middle to the ends.
Oblong – is a shoebox shaped blade, with both sides more or less parallel.
Linear – is an obelisk shaped blade with both sides parallel to the tip.
Lanceolate – a knife shaped blade with a broad base that gradually tapers to the tip.
Orbicular – is a round shaped blade.
Cordate – is a heart shaped blade.
Hastate – is an arrowhead shaped blade with two basal appendages that point straight out.
Saggittate – is an arrowhead shaped blade with two basal appendages that point down
along side the petiole.
* The prefix ob- means that the blade shape is inverted – a lanceolate shaped leaf upside
down is thus oblanceolate.
** It is common practice to use two or more terms to describe intermediate shapes,
hyphenating the terms used; thus a leaf that is intermediate between ovate and lanceolate
in outline may be termed ovate-lanceolate.
Leaf Apices and Bases
A number of terms are used to describe the shape of the tip (apex) or base of a blade.
Some common terms used include:
Tips
Acute – is a blade tip shaped like a football.
Acuminate – is a blade tip starting deep in the leaf and ending in a long taper.
Obtuse – is a blade tip that is round.
Emarginate – is a blade tip with a notch in the middle.
Mucronate – is a blade tip with a tiny, usually stiff, point.
Truncate – is a blade tip with a straight cut across (flat top).
Retuse – is a blade tip with a round sinus in the middle.
Bases
Acute – a blade base shaped like a football.
Rounded – is a blade base that is round.
Cuneate – is a blade base that is wedge shaped.
Hastate – is a blade base with two appendages that point straight out.
Sagittate – is a blade base with two appendages that point straight down.
Truncate – is a blade base with a straight cut across (flat top).
Cordate – is a blade base shaped like the two lobes of a heart.
Oblique – is a blade base that is unequal; one side of the blade is located lower on the
petiole than the blade on the opposite side.
Modified Stems and Leaves
Some plants produce modified leaves and stems that are somewhat different from the
ordinary foliage and stems of a typical plant. For example, tulips produce bulbs, which
are modified stems that produce fleshy leaves surrounded by bulb scales. The following
are terms used to define modified stems and leaves:
Tendril – is a modified leaf that coils around another plant or structure.
Aerial root – is a modified root system used to attach to another plant or structure.
Thorn – is a modified stem that forms a sharp tip (e.g. Natal Plum).
Spines – is a modified leaf that forms a narrow sharp tip (e.g. Cactus).
Prickles – is modified epidermis (skin) that produces a sharp tip (e.g. Rose).