Looks like a plant but is really a
• Most seaweed is photosynthetic.
• Some are not producers but parasites of other
• Seaweeds transform solar energy into chemical energy
in the form of organic matter.
• This organic matter is available to many other
• Seaweed is a type of marine algae, it can also be
referred to as a macrophyte or macroalgae.
• Seaweed is multicellular and eukaryotic.
• Seaweeds lack highly specialized structures and
reproductive structures that are characteristic of
terrestrial plants.
• Seaweeds show a wide range of growth forms and
complexity of structures.
• Seaweeds lack true leaves and roots.
• The complete body is called the thallus. It can be a
filament, thin leafy sheet or giant kelp.
• The leaf like, flattened portion of the thallus is known
as the blade, these have no veins.
• Gas-filled bladders, called pneumatocysts, sometimes
keep the blades close to the sea surface.
• Some have a distant stem-like structure that provides
support, this is called the stipe.
• Blades originate from the stipe.
• A structure that looks like roots attach the thallus to the
bottom. This is called the holdfast.
• These help anchor the seaweed. They cannot usually
cannot anchor in soft sediments and are restricted to
hard bottoms.
• These do not penetrate through sand or mud like true
roots do, so they are not involved in the absorption of
water and nutrients.
• They also usually lack tissues specialized in the
transport of water and nutrients. Water and nutrients
are picked up across the surface of the thallus.