I was nibbling on some nori the other day when a thought suddenly hit me. I don't know squat about algae. I know it comes in many shapes, sizes, and colors. I know it is that stuff that we used to throw at each other on the beach. I know that it photosynthesizes. That's about it. What is algae? Are they even plants?
The shortest answer I can give you is "it depends." If you are talking about nori for instance, then yes, technically they belong in the plant kingdom. Nori is made from algae in the genus Porphyra, which is a type of Rhodophyta or red algae. Together with Chlorophyta (the green algae), they make up some of the most familiar groups of algae. These groups differ from higher land plants in some pretty major ways. They lack adaptations such as leaves, roots, and do not contain specialized vascular tissues. However, even the term algae is a bit nebulous in itself.
In Latin, the word "alga" simply means "seaweed." Algae are paraphyletic, meaning they do not share a common ancestor. In fact, without specification, algae may refer to 4 entirely different kingdoms of life, Kingdom Plantae, Chromista, Protista, or Bacteria. Taxonomy being what it is, these may differ depending on who you ask. The point I am trying to make here is that algae are quite diverse from an evolutionary standpoint. Even calling them seaweed is a bit misleading as many different species of algae can be found growing on land.
Take for instance what is referred to as cyanobacteria. Known commonly as blue-green algae, colonies of these photosynthetic bacteria represent some of the early evidence of life in the fossil record. Remains of colonial blue-green algae have been found in rocks dating back roughly 4 billion years. As a whole, these types of fossils represent nearly 7/8th of the history of life on this planet! Diatoms (Chromista) are another enormously important group. The single celled, photosynthetic organisms are encased in beautiful glass shells that make up entire layers of geologic strata. They comprise a majority of the phytoplankton in the world's oceans and are important indicators of climate.
However, to bring it back to plants, there is one group of algae that really started it all. It is widely believed that land plants share an evolutionary history with a branch of green algae known as the stoneworts or Charas. These aquatic, multicellular algae superficially resemble plants with their stalked appearance and radial leaflets. It is likely that land plants evolved from a Chara-like ancestor resembling modern day liverworts living in shallow freshwater inlets. Estimates of when this happen go back as far as 500 million years before present. Unfortunately, fossil evidence is sparse for this sort of thing and mostly comes in the form of fossilized spores.
A couple bites of nori turned into a few hours of my morning. Algae are more diverse that I ever realized. All of this time I was either eating them or scraping them off of the glass of my aquarium. I have a new found respect for these organisms. We all should really. Even today, their importance in the environment goes largely overlooked.
Photo Credits: Proyecto Agua (http://bit.ly/1CxAvay), sunphlo (http://bit.ly/1J977Kl), Richard Ling (http://bit.ly/1xSoqJ1),