Bark
Vascular tissue
Xylem and phloem
Bark is the non-technical term
for the outer layers of a woody
stem.
Pith
Cortex
Botanically “bark” is called the
periderm on younger stems and
a combination of periderm and
rhytoderm on older stems.
Periderm
Vascular tissue
Xylem and phloem
Pith
Cortex
Periderm
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Bark
Periderm
The periderm is an actively
growing tissue that takes on
the role of the epidermis and
functions as a protective layer.
Periderm
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Cork
cambium
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Vascular
cambium
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Bark
Periderm
The periderm is designed to
divide and grow as the stem
enlarges with age.
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Periderm
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Bark
Periderm
The periderm is made of three
layers.
The outer phellem (or cork) layer.
The middle phellogen (cork cambium).
This layer divides to create phellem
to one side and phelloderm on the
other.
And the inner phelloderm, which is
living parenchyma cells formed to
the inner side of the periderm.
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Bark
Periderm
A stem will produce wound periderm in
response to injury or pruning.
Periderm
It will continue to grow until it covers
and seals the wounded area.
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Bark
Rhytidome
As a tree grows older, there is an
accumulation of dead, corky (suberized)
cells in the outer layers.
This is called the rhytidome and it covers
the still actively growing periderm.
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Bark
Rhytidome
In most shrubs, the outer cork layer is
limited in growth or falls away so does
not develop a thick bark layer.
Oakleaf hydrangea (Hydrangea quercifolia)
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Seven Sons plant (Heptacodium)
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Bark
Rhytidome
The periderm does not always grow
symmetrically and may deposit cork along
linear planes that form corky wings.
Winged euonymus (Euonymus alatus)
Winged elm (Ulmus alata)
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Bark
Rhytidome
In many cases, the rhytoderm is
persistent and forms outer scales as in
pine, or a more net-like pattern as in ash.
Pine (Pinus)
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Ash (Fraxinus)
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Bark
Rhytidome
The rhytoderm in some species is not
persistent and exfoliates or falls off.
The bark may exfoliate as patches or
scales as in sycamore and lacebark pine.
Lacebark pine (Pinus bungeana)
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Sycamore (Platanus)
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Bark
Rhytidome
The bark may also exfoliate in fibrous
paper-like layers as in some paperbark
maple and river birch.
Paperbark (Acer griseum)
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River birch (Betula nigra)
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Bark
Rhytidome
In some cases, there is limited rhytidome
development and older stems (trunks)
remain relatively smooth.
European beech (Fagus sylvatica)
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Magnolia hypoleuca
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Bark
Rhytidome
The color, texture and cracks in the bark can
be ornamental and help identify a plant.
European birch
(Betula pendula)
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David maple
(Acer davidii)
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Japanese maple
(Acer palmatum
‘Sango Kaku’)
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Amur cherry
(Prunus maackii)
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Bark
Rhytidome
One of the most interesting and useful
bark products is found in the
Mediterranean cork oak (Quercus suber).
The bark is striped from mature trees and
used to make products like wine corks.
Pith
Bark striped
away.
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Bark intact
for future
harvest.
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