Algal Morphology
I. Internal thallus morphologies
II. External thallus morphologies
III. Algal Growth
Unicells- solitary cells can be motile or non motile
ex. Chlamydomonas
Colony- an assemblage of individual cells, variable or
predictable
d
bl number
b of
f cells,
ll flagellated
fl
ll
d or non motile
l
coenobium- predictable number
and arrangement of cells
ex. Volvox
Filamentous- daughter cells remain attached to each other
following cell division forming a chain of cells
Coenocytic/ Siphononous– one large multi-nucleate cell
lacking crosswalls
Uniseriate- cells occuring in a single row
Utricles -swollen, terminal
end of the siphon
Multiseriate- consisting of
several rows of cells in a
longitudinal series in one or
two planes
Codium
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Limited cell differentiation compared to terrestrial plants…
Terrestrial Leaf
Coenocytic thallus construction -
Algal blade
What does this allow?
• Chloroplast movement
What special issues does it raise?
• Herbivory – healing
• Well developed cytoskeleton
• Repairs membrane in 1-2 seconds
• cuticle
• parenchyma (palisade, spongy)
• veins
• epidermal
• guard cells
Medulla
• stomates
Cortex-pigmented cortical cells
– unpigmented medullary cells
Pseudoparenchyma- form of thallus composed of interwoven
continuous filaments, superficially resembles
parenchyma
Parenchyma – undifferentiated, isodiometric cells
generated by a meristem
Cells division in any plane , not filamentous
Sarcodiotheca
Filaments
Hypnea
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Parenchymatous
vs.
Pseudoparenchymatous
Polysiphonous – composed of tiers of vertically elongated
cells, transversely arranged, the lateral cells around a
central axis (siphon)
Reds only
central cell surrounded by 4 or more pericentral cells
Polysiphonia
Petalonia
Mazzaella
Cortication – elaboration of polysiphonous condition where pericentral
cells continue to proliferate
Filament
(Central Tissue)
Ceramium nitens
Cortical Cells
(Outer Tissue)
Complete Cortication
Ceramium
Cortical Cells
(Banded Pattern)
Partial Cortication
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II. External thallus morphologies
Algal morphology:
sori
Can affect:
thallus
blade
- Photosynthesis
- Nutrient uptake
stipe
- Resistance to herbivory
holdfast
- Resistance to physical disturbance (e.g. wave stress)
Chaetomorpha
Filamentous
non-branching forms
branching forms
Filamentous
Chaetomorpha
Cladophora
Derbesia
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Prostrate / Procumbent: trailing on the ground
Foliose = a sheet of cells, blade like, no stipe
Monostromatic – one cell thick
Distromatic - two cells thick
Polystromatic – many cells thick
Codium
Petrospongium
Crustose Grows flat along the substrate; crust-like.
Ulva
Hildenbrandia
Bladed- flattened leaf like thallus, may have a stipe
Ralfsia
Stipitate = has a stipe
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Saccate = sac-like
Pneumatocysts-a large float containing gas found in heterokontophyta
-provide buoyancy to lift the blades toward the surface,
allowing them to receive more sunlight for Ps
- can hold O2, CO2, CO
Botryocladia
Cystoseria osmundacea
Halosaccion
Midrib-thickened longitudinal axis of flattened
branch or blade
-catenate series
Sargassum muticum
-singly
Midvein-a delicate median line of cells,
the blade is thicker through this region
Alaria fistulosa
Undaria sp.
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Tubular- tube of cells, hollow in center
Geniculate corallines
Geniculum
(flexible joint)
Intergeniculum
(hard part
between genicula)
• upright
•articulated
•geniculate
Non-geniculate corallines
Calliarthron cheiliosporiodes
Branched- axillary divisions
• crustose
• encrusting
encrustin
•non - geniculate
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Dichotomous/Bifurcate
Pectinate/Secund
Whorled/Verticillate
Pinnate-feather-like, regular opposite branching, distichous
Distichous-branching on both side of the axis, irregular,
opposite or alternate
Monopodial-having a distinct main axis of continuous
growth & giving off branchlets
Sympodial- apparent main axis does not extend by continuous
growth
Opposite
Alternate
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Holdfast Types:
III. Algal growth
Discoid Disc-shaped holdfast
apical
Hapterous- network of small branches
intercallary
basal
Stolon/Rhizome Creeping vegetative branch can also give
rise to new plants
Simple modified basal cell- one cell attached to the substrate
Apical growth =Apical cell or apical meristem
Where on the algal thallus does cell division occur?
“Meristem” = area of cell division and growth
Multiaxial- several longitudinal medullary filaments,
each derived from an apical cell
Pikea
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Uniaxial- one longitudinal central filament forming the axis
Apical around margin
Intercalary
Intercalary growth
Diffuse growth =
No defined area of cell division or growth;
occurs throughout the thallus
“transition zone”
• Growth in both directions away from meristem
• Usually between stipe and blade (or blade and pneumatocyst)
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Trichothallic Growth: Cells divide to form hair (filament)
above and thallus below
Heterotrichous growth – filamentous growth in 2 directions, results
in thallus composed of both prostrate + erect components
(in this case, psuedoparenchymatous polysiphonous…)
Polysiphonia
Upright Form
Filaments
Thallus
Prostrate Form
(Crustose, spreading)
Lithophyllum congestum
Anticlinal Pattern of cell division perpendicular to surface of algae.
Periclinal Cell division parallel to surface of plant.
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