Seaweed & Algae

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Although they are in the same family and all usually lumped as algae.. there are some differences...

Algae are very simple chlorophyll-containing organisms: some say that they are plants; other say that the are not, calling them Protists or Protoctists. We use the term "algae" very loosely because defining them is very difficult. In general, we can say that they are simple organisms composed of one cell, or grouped together in colonies, or as organisms with many cells, sometimes collaborating together as simple tissues.

Seaweeds are algae that live in the sea or in brackish water. Scientists often call them "benthic marine algae", which just means "attached algae that live in the sea". They come in three basic colours: red, green, and brown, as shown on the right on an Irish shore: dulse is the red seaweed; green sea lettuce is on the bottom right; and the brown plant with the midrib (a central thickening) is a young wrack. Red and brown algae are almost exclusively marine, whilst green algae are also common in freshwater (rivers and lakes), and in terrestrial (rocks, walls, houses, even trees) situations.

Many of these algae are very ancient organisms, and although lumped together as "algae", are not actually very closely related, having representatives in 4 of the 5 kingdoms of organisms.

Seaweeds are far more complex organisms than generally realised. Many have complex tissues and growth forms. They may have very complicated sex, with many of them producing sex pheremones, and with many different types of sex organs. Red algae have the most complicated sex known in plants. Kelps are known to have quite rapid translocation, something that is not credited to algae in many textbooks. There is even evidence emerging of root-like structures in some wracks that reach deep into rocks.

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What is a weed? A plant whose virtues have not yet been discovered.