Algae

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See Algae in Wikipedia, the free encyclopedia.

The term "Algae" refers to various "simple" plants, such as the Green Algae and the Charophyta, as well as any of the various groups of photosynthetic protists, as well as some of their relatives (i.e., "Oomycota").

The variety of algae run the gamut from microscopic cells, such as Euglena, to massive multicellular organisms such as the gargantuan, 36-meter long Bull Kelp, Nereocystis luetkeana.

Unlike true plants, multicellular algae, i.e., kelp, bladderwrack, or sea palms, do not have true leaves, stems, or roots. Instead, the "body" of the alga is divided into the root-like holdfast, and the plant-like thallus. In brown algae, the thallus is further differentiated into the stem-like stipe and the leaf-like blade. Unlike true plants, the cellular tissues of the holdfast, stipe, blade or thallus are not differentiated from each other.

Eukaryotic algae are a polyphyletic group, as, each group obtained their chloroplasts independantly. Some groups, such as the Green and Red Algae, are presumed to have obtained their chloroplasts, when the ancestral protozoa phagocytosed cyanobacteria, but did not actually digest their prey. Others, such as Euglena and the Chlorarachniophytes, are presumed to have obtained their chloroplasts through phagocytosis or myzocytosis (where the cell contents of the prey are sucked out) of green or red algae. A similar situation to what the ancestral predatory protists went through occured when Paramecium have been observed injesting the green alga Chlorella, whereupon the Paramecium soon began minimizing its feeding habits.

Historically, cyanobacteria were considered algae ("blue-green algae"), but, being prokaryotes, they clearly don't belong there.

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