The 'biggest plant on earth' is a seagrass!

I saw a little while ago that the largest plant was some underwater plant, maybe seagrass, in the Med. I think it was near Sicily, but presumably the Ozzie version is even bigger. Meanwhile, this is a small part of the world's widest tree, in Kolkata.
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My understanding is that there is only a single root system, but I could be wrong.
I think so. I have seen the odd item about it. There are some oddly extensive botanical specimens, as well as fungi. At one time the largest biomass of any one clone was supposed to have been the daffodil 'Carlton'.
 
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