on the bottom of the lake. The latter sometimes float to the surface as large filamentous mats
and can clog intakes and waterways. The green algae have certain photosynthetic pigments in
common and most closely resemble land plants in this and some other respects. A single spinach
cell would, in many ways, be quite similar to a single green algal cell. As in all algae these
contain Chlorophyll a, the primary photosynthetic pigment. They also contain Chlorophyll b, a
common accessory pigment. Their cell walls contain cellulose just like land plants.
Green algae occur in both freshwater and marine environments. Ulva, mentioned as an
example before, is a marine alga that forms leaf-like growths resembling lettuce. And as with
lettuce, spinach and many green algae, Ulva is edible. (Here I make a distinction between
'edible', an objective judgment, and 'palatable', a subjective judgment.) Two macroalgae
commonly found in freshwater are related to each other: Chara (muskgrass) and Nitella. These
are common inhabitants of lake sediments in the littoral zone and are large enough to be
confused with vascular aquatic plants.
Some green algae float as plankton, dependent on water movements, others are
attached to surfaces, and others such as Chlamydomonas can swim quite well with the aid of
one or more flagella.
Diatoms and golden-brown algae - This group is sometimes separated into two or more
groups consisting of the diatoms and the golden-brown algae. The two groups are similar in their
pigment content that also includes Chlorophyll c, another accessory pigment, but they differ in
structure. The diatoms are the algae that formed diatomaceous earth, a common filter material
and they all form siliceous (glass) structures as their cell walls. These are called 'frustules' and
are often shown in microscopic illustrations because of their diverse and beautiful forms. They
are common to all waters except the most extreme thermal environments and they are among
the most ecologically important organisms on earth. The golden-brown algae also include
common planktonic forms such as Dinobryon, Mallomonas, and Synura. These algae do not
form the frustules of the diatoms but they often do have siliceous scales. Many of the golden-
brown algae can swim with the aid of their flagella. Diatoms, however, either do not move or
when attached to substrates can "glide" slowly without flagella. As plankton, the diatoms are
considered euplankton, completely subject to water movements.
Euglena-like algae - These algae are motile by means of flagella. The best known genus,
Euglena, is typical of the group. Among the well-known characteristics are several animal-like
characteristics including the absence of a cell wall (usually found in plants), active motility, and
the ability to ingest food particles. Please note that recently other algal forms have been found to
be able to ingest food particles as well. This mode of nutrition (mixotrophy) is still being
investigated for its importance in aquatic ecosystems. Members of the Euglena group store food
as a unique form of starch called paramylon. In contrast with other starches paramylon has the
curious property of not changing color in the presence of iodine. Some commonly encountered
genera of this group include Euglena, Phacus, and Trachelomonas.