Range of Thallus Structure in Algae

Algae are chlorophyll bearing autotrophic thallophytes, bounded by a cell wall. Algae represent the most diverse kingdom in form and structure with both prokaryotic and eukaryotic members.
Following is the summary chart showing the diversity in algal thallus organization.
Range of thallus structure in algae

Algal thallus organization can be broadly classified into Unicellular and multicellular thallus.
1. Unicellular
(a) Non-motile uni cellular: A single non-motile cell carrying out all essential functions of life.
     Flagella is absent
     Example – Chlorella, Synechococcus
(b) Motile unicellular: A single cell with flagella  for locomotion. This group varies greatly in size and shape. The  unicellular forms may be spherical, oblong, pear-shaped or sometimes
elongated bearing flagella
    Example – Chlamydomonas
2. Multicellular
Colony is formed by aggregation of individual cells.
a) Non motile colony
Individual cells in the colony lacks flagella.
often a coenobium
Coenobium: A colony with definite number of cells and having a constant shape and size
Example – Pediastrum, Scenedesmus

b) Motile colony
Individual cells in the colony possess flagella for locomotion.
Often a coenobium
Volvox (500-50000 cells) are interconnected with each other with division of labour.
Example – Volvox, Gonium

c) Palmelloid or amorphous colony:
Here numerous non-motile cells are embedded in a common mucilaginous matrix
Number, size or shape of cell is not constant unlike coenobium.
All cells are independent and fulfils all function of an individual.
Example – Tetraspora, Chlorosaccus, Palmella
d) Dendroid forms: tree-like
The plant body appears as ‘tree like’ under microscope.
Mucilage often seen at the base.
Example – Ecballocyctis, Dinobryon

e) Filamentous
Cells arranged one upon the other in a definite sequence or uniseriate row forming filament.
Filaments may be branched or unbranched.

e 1. Unbranched filaments: Cells arranged one above the other without any branching points.
Example – Spirogyra, Zygnema (free floating), Nostoc, Anabaena, Spirulina
Ulothrix, Oedogonium (attached to the substratum by a basal specialized cell)
e 2: Branched filaments: Filaments with branching often dichotomous branching.
Example –Cladophora, Pithophora, Bulbochaete

e 3. Psuedobranched: Appear like branched under microscope. Actually, branching is due to the close association of unbranched individual filaments
Example –Scytonema

f) Heterotrichous form (hetero: different, trichous: trichome or filament)
Presence of more than one type of filament
Plant body consists of a prostrate system from which an erect system develops (also called as primary projecting system). Branches may give rise to primary projecting system, secondary projecting system sometimes even tertiary projecting system
Example – Chlorophyceae: Drapanaldia, Stigeoclonium, Draparnaldiopsis, Fritschiella
Phaeophyceae- Ectocarpus
g) Siphonous forms
Elongated plant body without septation. Many nuclei present in a common protoplasm called as coenocytic condition
Multicellular plants lacking usual septation (Fritsch,1935)
Example- Vaucheria, Botrydium, Codium, Bryopsis
h) Pseudoparenchymatous
Two types: Uniaxial and multiaxial forms
a) Uniaxial
“Close juxtaposition of the branch systems of a single main axial thread which form the thallus “(Fritsch,1935)
Plant body consist of a one main pseudoparenchymatous axis and all others are side branches
Example: Batrachospermum, Dumontia
b) Multiaxial forms
Main axis made up of association of many pseudoparenchymatous threads, appearing as more than one axes.
Example: Polysiphonia, Chondrus
i) Parenchymatous forms
In some algae, cell division and associated septation in all planes lead to the formation of a parenchymatous body. Such algae are foliose and flat
Example: Chara, Dictyota,  Laminaris, Fucus, Macrocysytis
Some algae like Microcystis even possess sieve tube like structures similar to higher plants
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