Above ground: stems and leaves

stem tuber

modified stem used to store food underground (ex/potato)

bulb

(onion), short, flattened stem bearing fleshy, food-storing leaves

rhizome

underground, horizontal stem

Shoot system

mostly above ground

-stems, leaves, reproductive organs

-origin in plume of embryo

stem functions

support, conduction, photosynthesis, food storage

orient towards sun (support)

tropisms

food storage in stems

Modified stems can serve as food storage (mainly starches)

Plant stems characterized by presence of ___

nodes: points of attachments of leaves, spaced at regular intervals

internode

region of the stem - the area between two nodes - elongates early in its development to ensure separation of leaves

axillary bud

usually found in the axil - area between a leaf and the stem.

• It can give rise to a new shoot (axillary shoot) - with its own apical meristem

Identifying ___ can help you figure out where a leaf starts

the axillary bud

Apical meristem produces 3 types of primary meristematic tissue

protoderm: rise to epidermis

ground meristem: gives rise to ground tissue (photosynthetic, storage, support)

procambium: rise to vascular tissue (transport)

secondary growth

increase in thickness or girth of stem caused by division of secondary meristem

secondary (lateral) meristem consists of

vascular cambium and cork cambium

secondary tissue

periderm and wood and tertiary tissue (bark)

vascular cambium 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

-New layers of periderm are produced inside the older layers

gas exchange happens via

lenticels- elevated regions with large intercellular space

rhytidome

older layers of periderm, die and are pushed out - cracking and producing typical texture of bark

secondary growth-bark

all tissue external to the vascular cambium.

-inner bark: secondary phloem. The cortex, and the phelloderm

-outer bark: cork cambium and everything outside (periderm, cork, etc).

-protects plant against physical damage and prevents water loss

older layers of secondary phloem are ____

lost/crushed, makes bark thick

Secondary growth-wood

consists of the original pith, primary xylem and secondary xylem

vascular cambium divides in 2 directions

secondary phloem (outside) and secondary xylem(inside).

• Older (dead) layers of secondary xylem are retained - adding layers of wood

• As new layers of xylem are created, the pith tissue at the center may be destroyed

heartwood

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

• Darker in color• Tylosesvessel elements prevent water flow

sapwood

water-conducting xylem in the periphery of heartwood.

• Lighter in color

branching

Lateral (or axial) buds can give rise to branching -new stems.

2 types of branching

monopodial: buds do NOT degrade, and all shoots continue to grow

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

Plant growth forms

vines: climbing woody and herbaceous

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), rosette, erect, mat

leaves arise from shoot apical meristem through _____

leaf primordia

most leaves have ____ growth

determinate

true leaves subtend an ____ at their base and are ____

axillary bud, lateral

blade

(lamina) - 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 main vein

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

Is the arrangement of leaves on the stem.

• Number and arrangement of leaves is species dependent

3 main types of leaves phyllotaxy

1)Alternate: one leaf per node

2)Opposite (deccusate): pair of opposite leaves per node, each pair rotated 90 degrees

3)Opposite(distichous): pair of opposite leaves per node, all pairs in same plane

4)whorled: 3 or more leaves per node

simple leaf

blade is undivided

compound leaf

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

palmately compound

leaflets arise from a common point (resembles palm of 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 are ____ coming from the stem

vascular bundles

-main vein (usually midrib)

-secondary veins branch from main vein

-tertiary veins branch from secondary

3 main arrangements of veins

a) Parallel venation – runs longitudinally

b) Pinnate venation – branch from main vein

c) Palmate venation – arise from a single point at base of leaf

reticulate vs percurrent venation

reticulate: netlike pattern, percurrent: ladderlike pattern

Leaf margins

entire: smooth margin

undulate: wavy margin

palmately lobate: lobes outlining palmate venation

pinnately lobate: lobes outline pinnate venation

toothed leaves

Serrate = sharp teeth pointing forward

• Dentate = sharp, symmetrical teeth

• Crennate = teeth are rounded

leaf shapes

• Ovate - are widest towards the base

• Obovate - are widest towards the apex

• Elliptic - single wide middle portion

• Oblong - longer wide middle portion

• Linear - long and thin

• Lanceolate - lance shaped (intermediate between ovate and linear)

leaf shape-tips and bases

• Rounded

• Acute - less than 90o angle

• Obtuse - greater than 90o angle

• Attenuate - tappering to a point

• Acuminate - curving inward to a point

• Cuneate - wedge-shaped (only base)

• Cordate - upside-down heart(only base)

hetrophylly

Some plants might have more than one type of leaf -juvenile vs adult, aquatic vs aerial, sun vs shade .For instance, in the common ivy, young leaves are palmately lobate, and older leaves are entire