What
is an Algae?
I was hoping you wouldn't ask that question.
In its broadest sense, the algae are photosynthetic organisms that do not belong to any of the major phyla of land plants (either vascular plants or bryophytes).
Traditionally algae
are photosynthetic Protozoa.
Some scientists only consider the eukaryotic phyla to be "true" algae.
Some now exclude certain eukaryotic phyla with weird traits (notably the Dinozoa
and the Euglenophyta) that are said to be secondarily photosynthetic (meaning
that they obtained their photosynthesis from some other cell that they absorbed).
This is an example of the problems that arise from the difference between taxonomy and phylogeny.
Algae have very few universal characteristics:
Most but not all are aquatic.
Not necessarily small.
Not necessarily unicellular.
Can be arranged in filaments, sheets or other structures.
Can be coenocytic (e.g. Caulerpa).
Cell walls made from cellulose or any of a long list of other polysaccharides.
Many different reproductive strategies.
Many different shapes, sizes, colors, life styles.
Biochemically and genetically diverse.
Very ancient... the different lineages diverged a long time ago. Groups are
not necessarily closely related.
The
group "algae" (as defined in the broad sense above) is certainly not
a clade because the most recent common ancestor of all the various algal phyla
lived such a long time ago that it is also the ancestor of animals and plants!
Taxonomy complicated by frequent endosymbiosis.
Since most algae defy the traditional description of Kingdom Protista (small
and unicellular), the Kingdom is now often referred to as the Protoctista.
Prokaryotic Algae:
Cyanobacteria (formerly blue-green algae)
Can be any color, but "typical" forms are a bluish-greenish-cyan color.
http://www-cyanosite.bio.purdue.edu/images/images.html
Oscillatoria
http://botit.botany.wisc.edu/images/130/Bacteria/Cyanobacteria/Oscillatoria/Oscillatoria_MC.html
Eukaryotic (true algae)
Kingdom Protista or Protoctista, sometimes placed in sub kingdom Protophyta
(as opposed to Protozoa)
Rhodophyta - red algae (phylum)
Mainly seaweed-like and marine.
http://www.sonoma.edu/biology/algae/Red.html
Examples include:
Porphyra - nori (sushi seaweed)
http://www.sonoma.edu/biology/algae/Porphyra.html
Many
individuals pressed into square sheets and dried.
Coralline algae
http://www.globaldialog.com/~jrice/algae_page/algae_gallery.htm
A
group of marine species
that secrete calcium carbonate as they grows to form rocky or stony structures.
Very important tropical reef builders. Contribute more rocky material to reefs
than the corals do.
Gelidium
http://www.sonoma.edu/biology/algae/Gelidium.html
We get agar from this genus - used to make agar plates. Also important as a thickener in many foods and condiments.
Phaeophyta - brown algae (phylum, group
of related phyla, who knows? Several different taxonomic schemes have been suggested
by different scientists)
Mainly
seaweed-like, and marine.
Some microscopic forms in marine and freshwater.
http://www.sonoma.edu/biology/algae/Brown.html
Examples include:
Fucus
http://www.sonoma.edu/biology/algae/Fucus.html
Nereocystis (kelp)
http://www.sonoma.edu/biology/algae/Nereocystis.html
Chrysophytes - microscopic brown algae, often single celled, usually swim using
flagella.
Diatoms
http://www.umich.edu/~phytolab/GreatLakesDiatomHomePage/groups/majorgroups.html
Microscopic brown algae with cell walls made of silica (glass).
Extremely
common in all aquatic environments, form a brownish film on almost any surface.
Also called Bacillariophyceae.
The cell walls are known for their elaborate shape and surface features, which
is usually characteristic for each of the many species.
Accumulated diatom shells form a white powder called "diatomaceous earth",
which has a number of commercial uses, mainly as an abrasive.
Chlorophyta - green algae (phylum)
Seaweed-like and microscopic forms. Slightly more freshwater species than marine.
http://www.sonoma.edu/biology/algae/Green.html
http://botit.botany.wisc.edu/images/130/Chlorophyta/
Many classes and orders of green algae:
http://tolweb.org/tree?group=Green_Plants&contgroup=Eukaryotes
Three examples
of important classes are:
1) Ulvophyceae
(green, seaweed - like, generally filaments or sheets)
http://www.bio.mtu.edu/~jkoyadom/algae_webpage/ALGAL_PAGES/ulvophyceae.htm
Examples of the phylum Chlorophyta, class Ulvophyceae include:
Ulva
http://www.sonoma.edu/biology/algae/Ulvafen.html
"Sea lettuce". Common marine species found all over the world. Usually grows as green sheets.
Caulerpa
http://www.globaldialog.com/~jrice/algae_page/feathercaulerpa.htm
Marine
alga often used as ornamental species in marine aquaria. Many species, each
with distinct, sometimes plant-like, pleasant-looking fronds.
Caulerpa invasion! Caulerpa taxifolia has become an ecological problem
because of its ability to escape from aquaria and establish itself in non-native
environments.
http://www.coastalconservancy.ca.gov/scwrp/BOGMtgs/BOG102000/Caulerpa.htm
http://www.cosmiverse.com/science070702.html
Cladophora (image here).
Filamentous green algae with freshwater and marine species. Thrives in nutrient-rich freshwater ponds, lakes and bays. Almost totally overgrew parts of lake Erie in the past.
2) Chlorophyceae
(generally microscopic - cause green pond water)
http://www.ucmp.berkeley.edu/greenalgae/chlorophyceae.html
http://www.bio.mtu.edu/~jkoyadom/algae_webpage/ALGAL_PAGES/chlorophyceae.htm
Examples:
Chlamydomonas (image)
Ankistrodesmus (image)
Scenedesmus (image)
Volvox (image)
3) Charophyceae
(Green, plant-like ancestor of the land plants, sometimes called stoneworts.)
http://www.bio.mtu.edu/~jkoyadom/algae_webpage/ALGAL_PAGES/charophyceae.htm
Examples:
Chara (image here)
Choleochaete (related to common ancestor of ALL green plants)
Most
important feature is the fact that this species protects it's fertilized embryo
in a special structure, much like the land plants do.
Problems involved with getting onto land:
http://www.mansfield.ohio-state.edu/~sabedon/campbl29.htm#plant_terrestrial_adaptations
Other eukaryotes that may not really be algae at all, but they sure look like it.
Generally these are non-photynthetic protozoans, unrelated to the other algae that at some point have acquired chloroplasts from some other organism that they basically swallowed. In most cases, the organism they swallowed was also a eukaryote. When this happens the "swallowee" gradually degenerates and loses many of its original parts. The true nature of these organisms has been unraveled mainly using DNA sequence techniques. At one time they were classified as algae. This is one reason why the "dinoflagellates" have been renamed "dinozoa".
Euglena
http://staff.jccc.net/pdecell/protista/euglena.html
http://www.jracademy.com/~mlechner/archive1999/euglena.html
Dinozoa. Sometimes called dinoflagellates, or dinophyta. Actually related to
protozoans like amoeba, paramecium and the organism that causes malaria. Contains
one or more brownish chloroplasts that appear to have at one time belonged to
an endosymbiotic chrysophyte (Phaeophyta).
http://www.ucmp.berkeley.edu/protista/dinoflagmm.html
http://fig.cox.miami.edu/~161hon3/temp1.htm
Variety of shapes
and colors. Sometimes called "golden brown algae".
Responsible for red tides, which are huge blooms of rapidly growing dinozoans
caused by elevated nutrient levels in marine environments. Red tides are often
a sign of pollution and may kill other marine life in the area.
Dinozoans like to form symbiotic relationships. Some Dinozoans live inside the
tissues of corals and other animals as ZOOXANTHELLAE. Contribute to the nutrition
of these animals in exchange for a safe place to live. Physiological stress
can cause corals to evict their dinozoan guests, a phenomenon called "coral
bleaching". Unfortunately this is often fatal to the coral. This phenomenon
is partly responsible for the global decline of coral reef environments.
More symbiosis stuff:
Paramecium
and the chlorophycean algae Chlorella.
http://botit.botany.wisc.edu/images/130/Symbiosis/Paramecium_Chlorella.html
Cryptomonas - cyanobacteria in a red algae in a brown algae.
(red algae nucleus reduced to nucleoid)
http://www.bio.mtu.edu/~jkoyadom/algae_webpage/ALGAL_PAGES/cryptophyta.htm
Gymnodinium acidotum - cyanobacterium in a red algae in a brown algae
(red algae nucleus reduced to nucleoid) in a dinozoan. Confused? You should
be. This thing is weird.
Learn more.
Amphiscolops (flatworm containing Amphidinium, a dinozoan.)
Plates from an OSU study of this organism:
