The term "algae" is used to collectively refer to a wide range (20,000-30,000 spp.) of very simple photosynthetic organisms. While this term is no longer used as a taxonomic grouping, it is still useful for referring informally to these photosynthetic protists. (Protists are diverse eukaryotes which are neither fungi, animals nor plants.)
The earliest multicellular alga known is the red fossil alga Bangiomorpha (at right), found in 1,200 million year old rocks in Arctic Canada. What's more this is the first known organism to show sexual reproduction.== Chapter 9. Phycology ~ The Algae == The algae (singular: alga) comprise several different groups of plant-like organisms, some of which are (and some are not) regarded as members of the Kingdom Plantae. All algae lack true leaves, roots, flowers, and other structures found in the higher plants. They are distinguished from bacteria and protozoa mainly in that they are autotrophic, obtaining energy through photosynthesis. Although no longer considered a natural group, the term algae is still used for convenience. The botanical discipline concerned with the study of algae is called Phycology (or sometimes, Algology); and the environments most phycologists (or algologists) focus on are the marine intertidal/shallow subtidal regions of the world oceans. It is in these environments that the diversity of structurally complex algae (called seaweeds) reaches its pinnacle.
As a grouping, the algae cut across even the prokaryote/eukaryote divide: the so-called "Blue-green algae" are cyanobacteria. All other algae are eukaryotes. Green Algae (different from Blue-green algae) are considered to be the ancestors of green plants. Other kinds of algae on the other hand are distinct from green plants and from each other in having different and unrelated accessory pigments. These pigments are responsible for the ways different algae absorb light, providing advantage to each individual type of alga to compete best at a water depth where its preferred wavelength is perhaps strongest.
The cyanobacteria comprise the structurally simplest algae, and presumably are closely related to the oldest photosynthetic organisms on the planet. Although capable of extracting energy from sunlight through photosynthesis, these algae are related to bacteria as evidenced by their prokaryotic cell structure. Yet, some Blue-greens have developed multi-cellular thalli that approach eukaryotic algal forms, and thus their traditional inclusion within the "algae."
- Read Cyanobacteria
8.1 How do we know that the different algae are not monophyletic?
8.2 What do the different algae have in common that they are grouped together as algae?
8.3 What are 3 similarities between the green algae and green plants?
8.4 Define endosymbiosis. Did photosynthetic cyanobacteria exist before or after photosynthetic organelles? Why or why not?
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Chapter 7 - Plant Systematics ~ :Chapter 8 - Microbiology ~ Chapter 9 - Algae