Algae is a plant ... in the past they were all considered to share a common ancestor ( monophyletic ) so were all grouped in the Plant kingdom ... today they are thought to have different ancestors ( polyphyletic ) and are placed in several different divisions within the Plant kingdom while unicellular and colonial algae are placed in seperate kingdom Protista ( these would not be plants since they are not multicellular despite the fact they are photosynthetic ).

Keep in mind there are bacteria capable of photosynthesis but these are all placed in the kingdom Monera which contains the bacteria and "Blue Green Algae" ... due primarily to there cell structure ( they are prokaryotic and not eukaryotic like members of the Plant kingdom ... and they are also single celled organisms amongst other differences )

It's also interesting that Fungi also were once placed in the plant Kingdom but now are placed in the Kingdom Fungi.

Good Day ...

Algae are a subgroup of plants ... so they are indeed plants ... some algae have been moved to the kingdom Protista and in this case it can be said they are not plants ... Kelp is an example of a plant that is also an Algae.

At least according to Bold's "The Plant Kingdom" ...

An eight kingdom system ??? ... eeesh

Good Day ...

Hi
What about the things found at the bottom of the ocean.??
They are extracting checicals directly from seawater.
They are obviously not plant nor animal so would assume they must create a new kingdom for them??
The most common name I've heard is "worm" lol Definitely not a worm .
Algae,is one of the most fascinating live forms particularly the marine types. Gave up long ago trying to tell one from another lol. I just take their word for it.
Another question about naming I've always wondered about.
If life is discovered on another planet will a new kingdom have to be created or will they use the standard approach and classify it by earth standards?? Given how resourceful and adaptable algae is I'd bet money that it's the most likely to survive the extremes of even our nearest neighbors.
Gary

Algae are plants, are multicellular eukaryotic photsynthetic organisms. They can be unicellular (ex Chlamydomonas) or multicellular (ex. Giant kelp ; Macrocystis).
The difference between an alga and a superior plant is for example the lack of roots (usually) and of vascular tissue (xylem, phloem).
Blue green algae are NOT algae, and they are not plants. They were thought to be algae, and hence were named according to the binomial nomenclature. IT was sometime in the 70s (or 80s) that they were reclassified by Rippka et al. as bacteria. Blue green algae, which should be called cyanobacteria, are prokaryotic photosynthetic organisms. As Kelly mentionned plants come from the symbiosis of a non photosynthetic organism (the plant ancestor) and a cyanobacterium. The cyanobacterium was engulfed and somehow was not decomposed (as food) and not only stayed in the cell ,but found a new function : providing the cell with sugars (from photosynthesis).
It is therefore not surprising that Chloroplasts (ancient cyanobacteria that were engulfed) replicate independently from the plant cell, the same way that mitochondria do.
Gary, are you talking about Anemones? These things are so weird! both plant and animal and none of each!

"If life is discovered on another planet will a new kingdom have to be created or will they use the standard approach and classify it by earth standards?? "

The BIG question to be anticipated ... depends on what we find and what we think it is ? ... If we find life on Mars .. did life originate on that planet and come to Earth or did life evolve independently on Earth and Mars ?? If life started independently on both planets maybe we would have a super taxa above Kingdom ... if life started on Mars and came to the Earth maybe it can be placed in an existing kingdom ...

Who knows ??

Good Day ...

Nazanine
Well not only the Anemones but the Corals ,Crinoids.Gorgonians and photosynthetic clams. Then even more plant-like the calcereous algaes and the highly developed algaes such as Calerpas and Udoteas.
At the extreme depths of the ocean there exist totally unknown genus of plantanimals that rely on extration of chemicals directly from the ocean appraently depending on heat from volcanic vents.They do appear "wormlike" but obviously will require a whole new catagory of life.
Mojave Kid
That "contamination "theory is fascinating isn't it?? If Mars does prove to be older and that life once existed there
It would mean we know nothing about how planets are created.
or geology. lol Obviously matter can and does exchange between the planets but would it be possible for any lifeform to survive the trip?? One thing that can be said for sure.Martian life is rare and tiny.Anything above microscopic level would surely have been detected by now.
Personally I think that theory is a dead end.
Astronomy is changing so rapidly with the new tools being used it's easy to see already that we don't understand our own solar system. It's at least 4 times bigger and is globe shaped not a disc. The oort clouds and Kuiper belt not only exist they are the biggest part.!! Obviously this brings into serious question about how and when the solar system began and even more about why.
Would sure like to come back in say a hundred years from now and see how many of the present theories are still around.
Personally I think IF there is life out there.There will be a large assortment of algaes lol
Gary

As pointed out above, the general term "algae" takes in a lot of things that are only distantly related to each other. But the more specific group of "green algae" have much in common with each other and are a natural group (but paraphyletic, meaning another group that evolved from within them--land plants--has been classified as a separate group).

Whether algae are considered "plants" is really just a matter of where you draw your lines, and where you stick the labels. It's just semantics. Botanists agree that all green land plants (flowering plants, gymnosperms, ferns & fern allies, & bryophytes) had a common ancestor, and that that common ancestor was some kind of green algae. In other words, land plants are really just algae that learned to live on land. But botanists disagree on whether we should reserve the term "plant" for only the things that came onto land to live, or include their aquatic ancestors in the group.

Gary, those organisms that form the basis for the ecosystem at deep sea trenches are sulfate reducing bacteria. The bacteria derive thier energy from sulfate compounds in the sea water released at the geothermal vents. This heat and energy source forms the basis for that food chain. Those worms have symbiotic bacteria which provide the worm with energy via this inorganic energy source. Other "regular" animals go up from there, detritivores, true predators, etc.

I hope this confuses (does not confuse?) the issue further.

Also, plant is a common name, mostly, and as such you can call anything you want a plant, but if you want to be more accurate one needs to refer to its most accepted and widely used name, if in turmoil, or a cladistically valid name if further work has been done to elucidate that organism's relationships. Barring a well defined and agreed upon definition it's all a matter of just making sure other people know what you mean. Know what I mean?

Alan

so what's a slim mold :)

and gimmie 8 kindoms, this whole shoving stuff into places that aint quite right bugs me.

froggy

Alan
Thanks for the explanation. i didn't know much study had been done on these"animals" as yet. Obviously they don't fit into any known catagories of other marine "animals"
Mind boggling that anything could exist yet alone thrive at those pressures and total lack of light. The more studied
types susch as corals and clams almost defy classification.
They sure appear to be both a plant and an animal as two separate organisms .Appears one can't live without the other
but definitely different than an "organ"
Froggy How about mildew or Virus ?? i read a definition once of "Virus , a string of DNA with limited life functions". Surely they must be the smallest of functioning life forms.??
Gary

Gary--A lot of people consider viri to not be "alive". This is where it would help us to know the meaning of life! LOL

Viruses cannot reproduce on their own. They must first take over the workings of a cell before they can replicate, hence they are non-living. Virus is actually the best descriptor of what they are, provided you know what viruses do.

A recent theory is that chloroplasts originated from blue-green bacterial symbionts in the common ancestorof green plants, red algae and an obscure group called glaucophytes, and that the chloroplasts in brown and golden algae, etc. originated from red-algal internal symbionts.

What is the function of these esoteric splitter classifications? Who does what with such information as "[blue]-green algae are not considered Protists. They are a type of photosynthetic bacteria"? I've a degree in one of the biological sciences and never quite understood the emphasis on classification. Just curious, not fussing about anything that has been posted.

(My father-in-law just vegetates in a nursing home. Should we reclassify him? BG)

Good question ...

Our survival depends finding and discovering uses of our resourses on Earth ... a classification system allows one to better manage our living resourses ... the more accurate the system the better since closely related organisms should share simalar traits ...

Kinda like having some of your sox in your underwear draw and some of your shirts in the sox draw ... what happens when your house is on fire and the lights are out and you need to get out real fast !!

Many scientific studies could not be performed without an existing system of classification , identification and nomenclature.

There is also the more lofty goal of understanding how life evolved on Earth ... that is our past ... a better understanding of our presnt and maybe a hint of the future.

The fine details add up ... I would speculate.

Good Day ..

ALGAE ARE NOT PLANTS! They have some same characteristics, but they are not considered plants. It is thought that plants evolved from algae but that doesn't make it a plant.

I must say that I am very greatly impressed by the wealth of knowledge expressed in the answer to this question. Altho no real answer is forthcoming, it's fun and interesting to discuss taxonomy. Please continue this interesting discussion!