∞ generated and posted on 2016.12.04 ∞
Eukaryotic organisms that are photosynthetic and are not plants.
|The Algae all possess plastids, i.e., as equivalent to chloroplasts as found in plants, but are not plants, are highly diverse, range from unicellular to multicellular, and in fact are ancestral to land plants.|
Singular, alga; among algae types are green algae, brown algae, golden algae, red algae, diatoms, dinoflagellates, etc. All algae possess homologous though often greatly derived chloroplasts.
Figure legend: Some sort of multicellular alga found on the beach a few hours north of San Francisco (2011). Note that the image has been recolored a bit as it was very gray, foggy, and misty.
Historically certain kinds of bacteria have also been described as algae, particularly the so-called blue-green algae, though blue-green algae are actually bacteria, not eukaryotes (another, more modern name for blue-green algae is cyanobacteria).
Though certainly not all eukaryotic algae are unicellular nor small colonial forms, the smaller, especially unicellular members are microorganisms.
Note also the "not" in the definition, the presence of which often can be taxonomically problematic, typically implying a polyphyly, which indeed the algae constitute.