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Chlamydomonas spp., the dinoflagellates (Peridinium spp.), and others. Many of the
microscopic forms also form multicellular colonies or filaments of single cells. Examples include
colonial Volvox spp. and filamentous Oedogonium spp. There are thousands of microscopic
algal species.
In freshwater systems, there are also several genera that have cells and colonies large
enough to be easily visible. Sometimes these algae are included in manuals on identification and
control of aquatic plants. Chara spp., Nitella spp., and Hydrodictyon spp. are examples of such
"large" microscopic algae. All three of these belong to the green algae group although there are
other large freshwater forms in the red algal group.
In terms of phylogeny and physiology, the green algae are considered to have the most
characteristics in common with higher plants. A single spinach cell would have many of the same
structural and functional characteristics as, say, a single Chlorella spp. cell.
Major Algal Groups. Although this will be explained later in this section, there is one
algal group that is more like bacteria than other algae. The Cyanobacteria are described in a
section immediately following this one. All other groups of algae have characteristics in common
with higher plants and a cellular structure that includes membrane-bound organelles such as the
nucleus, chloroplasts, and mitochondria. This and other characteristics places them among the
eukaryotic organisms which include all multicellular plants and animals as well as many other
single-celled organisms that are animal-like.
Many biologists place the algae within the eukayotic group that also includes single-
celled animals and is called Phylum Protista. Although the algae are technically considered
single-celled organisms, as mentioned before, they can form multicelled colonies or multicelled
tissues that look very much like higher plants. When the algae form large structures that can be
collected by hand or viewed with the naked eye they are sometimes referred to as
"macroalgae". Examples of macroalgae include Ulva (sea lettuce), and the many kelps. The
difference is that the cells of these algae are still not completely modified into functional tissues
such as leaves or vascular tissue. In some cases, single cells taken from these complex
organisms can grow into new algal organisms. For a more complete discussion of the
differences, the reader should refer to a botany text or a college-level biology text.
The major groups of the algae include some that most people do not normally think
about outside of their school courses sometime in the past. The major groups are briefly outlined
as follows:
Green Algae - This extremely diverse group includes common filamentous and single-
celled organisms such as Spirogyra, Ulothrix, Cosmarium, Chlorella, Staurastrum, Pediastrum,
Scenedesmus, Volvox, Chlamydomonas, Pithophora, and Cladophora. This group also includes
species that form structures large enough to be easily seen without the aid of a microscope and
are considered "macroalgae". The green algae can bloom as thick planktonic suspensions of
single cells or colonies, or as thick mats of tangled filaments either attached to substrates or lying
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