I’ve always heard it is Pando, the aspen grove in south central Utah, which have an interconnected root system across 108 acres.
But recently there was the discovery of a seagrass meadow off the coast of Australia covering 70 square miles or almost 45,000 acres. The seagrass repeatedly clones itself and has the same DNA throughout the meadow.
So has Pando been dethroned, or is this just some other method of measuring the largest, like “on Thursdays on grass we are undefeated” ?
I understand what they’re saying, but I still don’t them as one organism, no more than I would of conjoined twins. It is, of course, a matter of definition, but if you cut one of those trees off underground, it would still go on much as before.
I’m not sure how it compares to the others but there is the humongous fungus:
I remember that X-Files episode!
I have always heard it was The Great Barrier Reef.
Edit: Its Wikipedia article says it is is the “world’s biggest single structure made by living organisms” so I guess it is NOT organism by itself.
I’ve looked at all the press reports and the original paper and general stuff about seagrass and I still cannot figure out in what sense a seagrass meadow is a single organism. The humungous fungus is physically one continuous thing underground. Is that true of seagrass? I man, it’s not enough to prove that it reproduces by cloning. It has to be physically one entity with some degree of shared metabolism.
Someone would need to do some math but, conceivably, there might be more vegetable mass in Utah, so they’d still have a claim.
I think it is like Pando…the Aspen grove mentioned in the OP.
In Pando, a tree sends roots out and then another tree pops up from that. Rinse and repeat.
In theory, you could pull on one tree/blade of grass and the whole lot would come out connected to that one piece.
At least, that is how I think of it.
Then we need to know what we mean by “biggest”. Are we talking about area covered or mass?
My sense of it was Pando was more massive and the humongous fungus was biggest (in area). Totally a WAG on my part though. I really do not know. Not sure where the sea grass fits in.
Funny thing…I was recently re-watching the X-Files.
Same thing that pops into my head any time I hear mention of a new world’s biggest organism.
Ditto the episode with the ice worms when mention is made of drilling down to places under the ice where life may exist.
I think largest single living organism means if something like a deadly bacteria, virus or poison were introduced into part of it, all of it would be affected, even die.
I see the idea you’re going for, but in practice I don’t see how a pathogen or a poison works as a rigorous test. It’s common for something to harm just one part of an organism and not spread.
Along similar lines, you could introduce an isotope-tagged basic nutrient that you could track to see if it moves through the organism. But again, if something is a single organism where everything is physically linked, you could still have a situation where something introduced at any given point only spreads to a certain distance from that point.
I think a bright line is going to be difficult.
More or less:
the plant has been able to continue growing through a vegetative growth extending its rhizomes outwards
Now, obviously parts of it may have broken off for various reasons and continued growing, but just as a form of growth, it could all be one organism, same as the aspen (where the same caveat holds, anyway)
There are potential studies that could be done to decide the matter, but personally, I’m happy to consider it one organism.
From your article:
I’ll let you take a minute to absorb the fact that pretty much every mushroom you’ve ever eaten has been fungus genitalia.
I’ve always detested mushrooms, now I have an excuse. 
Pando is the heaviest, the grass is bigger in 2-dimensional surface area. And maybe dethroned the mushrooms. Pando is also very old, but not the oldest.
But how do you know? Has it been weighed? I’m sure a theoretical calculation has been done, but the seagrass covers an area over 400 times that of Pando. While the height of an aspen tree is much taller than seagrass, the seagrass is also more closely bunched together than a grove of aspens.
Anyone interested in attempting the calc.?
Hopefully, the next time you stop to smell the roses, you don’t think too hard on what part of the flower that is.
A rose by any other name is still a spiky bush genital.
Re: Pando–if you’re ever in that area (kind of a back road route from Capitol Reef to I-70) it’s worth a detour. Largest organism or not, it’s a beautiful spot.
It’s not like they’ve exactly been subtle about it…