Seaweed
Seaweed refers to several species of macroscopic, multicellular, marine algae that live near the seabed (benthic).
The term includes some members of the red, brown, and green algae. Seaweeds can also be classified by use (as food, medicine, fertilizer, filtration, industrial, etc.). The study of seaweed is known as phycology.
Taxonomy
A seaweed may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae. As these three groups do not have a common multicellular ancestor, the seaweeds are in a polyphyletic group. In addition, some tuft-forming bluegreen algae (Cyanobacteria) are sometimes considered to be seaweeds — "seaweed" is a colloquial term and lacks a formal definition.
Structure
Seaweeds' appearance somewhat resembles non-arboreal terrestrial plants.
thallus: the algal body
- lamina or blade: a flattened structure that is somewhat leaf-like
- sorus: a spore cluster
- on Fucus, air bladder: a floatation-assisting organ on the blade
- on kelp, float: a floatation-assisting organ between the lamina and stipe
- stipe: a stem-like structure, may be absent
- holdfast: a specialized basal structure providing attachment to a surface, often a rock or another alga
- haptera: a finger-like extension of the holdfast anchoring to a benthic substrate