BIO 3015 - Above Ground: Stems and Leaves

Stem Tuber

A modified stem used to store food underground (ex. Potato)

Bulb

A short, flattened stem bearing fleshy, food-storing

leaves. (ex. Onion)

Rhizome

An underground, horizontal stem (ex. Ginger)

Shoot System

This system consists of stems, leaves, and reproductive organ. Mostly found above ground... although modified

stems (e.g. potatoes) and leaves (e.g. onions) grow

underground.

Stem Function - Support

Upholds leaves, flowers, and buds. Sometimes can help leaves orient towards Sun (tropisms)

Stem Function - Conduction

Moves water and minerals from roots to leaves, and

products of photosynthesis from leaves to the rest of the plant

Stem Function - Photosynthesis

Green stems are photosynthetic - sometimes the only

photosynthetic organ (e.g. cacti)

Food Storage

Modified stems can serve as food storage (mainly

starches)

Stems - Morphology

Plant stems are characterized by the presence of

nodes spaced at regular intervals. The internode region of the stem elongates early in its development to ensure separation of leaves.

Nodes

Points of attachment of leaves

Internode

Area between nodes

Axillary Bud

A structure that has the potential to form a lateral shoot, or branch. The bud appears in the angle formed between a leaf and a stem.

Axillary Shoot

A shoot that forms in tissue culture from a new bud formed during the micropropagation process; this type of shoot forms more slowly but with greater genetic uniformity

Primary Meristematic Tissue

Protoderm, Ground meristem, & Procambium

Protoderm

gives rise to epidermis

Ground Meristem

Gives rise to ground tissue (photosynthetic, storage, support)

Procambium

Gives rise to vascular tissue

(transport)

Secondary Growth

An increase in thickness or

girth of the stem caused by cell division of

secondary meristem

Secondary Meristem

This meristem consists of the vascular cambium and the cork cambium

Vascular Cambium

This divides into secondary xylem (inside) and secondary phloem (outside)

Cork Cambium

Produces periderm tissue

Secondary Growth - Periderm

Replaces the epidermis in shoots at the end of the first year of growth. It is mostly not permeable due to waxy suberin

Lenticels

Elevated regions with large intercellular space (Where gas exchange happens)

Rhytidome

Old layers of periderm that die and are pushed out of the bark , racking and producing typical texture of bark

Secondary Growth - Bark

Consists of all tissue external to the vascular cambium.

Inner Bark

Includes the secondary phloem. The cortex, and the phelloderm.

Outer Bark

The cork cambium and everything outside (periderm, cork, etc).

Wood

Consists of the original pith, primary xylem

and secondary xylem

Vascular Cambium - Wood

Divides in 2 directions - secondary phloem (outside) and secondary xylem (inside).

Heartwood

The oldest (inner most) layers of secondary xylem which NO longer conduct water

Tylosesvessel

Elements prevent water flow

Sapwood

Water-conducting xylem in the periphery of heartwood.

Twigs

Dormant stems of winter deciduous plants that are modified to facilitate overwintering.

Terminal Bud

Contains apical meristem and is protected by bud scales

Lateral Buds

Similar in structure to the terminal bud, but form at

each node.

Leaf Scars

Form where leaves fall off - they contain circular markings called bundle scars

Monopodial Branching

Buds do NOT degrade, and all shoots continue to grow

Sympodial Branching

Terminal buds degrade, and lateral buds closest to the apex become the new terminal shoot

Vines

Climbing woody and herbaceous plants

Trees

Woody plants with one main long-lived

trunk

Shrubs

Woody plants with multiple main long-

lived trunks/stems

Herbs

Herbaceous plants (no secondary

xylem) Ex. Rosette, Erect, Mat, etc.

Leaf Primordia

The place where leaves arise from the shoot apical meristem

Blade

Flat, usually widest, part of leaf

Petiole

Stem-like part of the leaf, collecting the

blade to the stem

Petiolate Leaves

Leaves containing visible petiole (usually attached to margin)

Sessile Leaves

Leaves without visible petiole

Midrib

Contains the main vein of the leaf

Peltate Leaves

Special type of petiolate leaves in which the petiole attaches underneath the blade (instead of margin)

Perfoliate Leaves

Special type of sessile leaves in which the stems passes through the center of the blade

Phyllotaxy

The arrangement of leaves on the stem.

Alternate

One leaf per node

Opposite (Deccusate)

A pair of opposite leaves per node. Each pair is rotated at 90o

Opposite (Distichous)

A pair of opposite leaves per node. All pairs in the same plane

Whorled

Three or more leaves per node

Simple Leaf

Blade of leaf is undivided

Compound Leaf

Blade is completely divided into leaflets. Notice position of axillary buds!

Palmately Compound

Leaflets radiate from a single point (resembles the palm of a hand)

Pinnately Compound

Leaves originate from the midrib (feather-like)

Doubly Compound

Rachis (stem-like structure) originate from midrib, and then divide into leaflets.

Leaf Veins

Vascular bundles coming from the stem. Main vein (usually the midrib). Secondary veins branch from main vein. Tertiary veins branch from secondary(etc)

Parallel Venation

Runs longitudinally on the leaf

Pinnate Venation

Branch from main vein of the leaf

Palmate Venation

Arise from a single point at base of leaf

Entire Margin

Smooth margin

Undulate Margin

Wavy margin

Palmately Lobate

Lobes outlining palmate venation

Pinnately Lobate

Lobes outlining Pinnate venation

Serrate Teeth

Sharp teeth pointing forward

Dentate Teeth

Sharp, symmetrical teeth

Crennate Teeth

Teeth are rounded

Ovate Shape

Are widest towards the base

Obovate Shape

Are widest towards the apex

Elliptic Shape

Single wide middle portion

Oblong Shape

Longer wide middele portion

Linear Shape

Long and thin

Lanceolate Shape

Lance shaped (intermediate between ovate and linear

Attenuate Tip

Tappering to a poin

Acuminate Tip

Curving inward to a point

Cuneate

Wedge-shaped (only base)

Cordate

Upside down heart base