“Green” marble is the crux. Easily stained and impossible to fix.

Sorry.

If it’s just one piece of marble it may be possible to replace but a difficult call from where I’m at.

Cleaning Marble: Baking Soda, Water & Lemon Juice.
Mix to a paste, rub all over and clean off

Try T cut (for cars) it also bings back the shine to scatched marble. What ever you do don’t put lemon juice on it, the acid will eat into the stone and leave a white mark.

make a paste out of baking soda and water. Make it kind of thick too.

Then take a damp cloth and scrub it. This may take a couple of trys, and some effort but it should work.

Then wipe of with wet rag and dry

you’re not going to remove any stain from any marble especially the green one just replace the piece if it’s in pieces or leave the plant where it is
flooring expert

On a day to day basis marble needs wiping with a damp soapy cloth.

As it is porous,it does stain easily.using half a lemon on stains will fade them but great care must be taken to prevent the acid affecting the marble.
It is best to leave the lemon for just a couple of minutes,then rinse the area well and repeat the the procedure several times,so that the marble can be checked for signs of any damage.

try with White Spirits or pure soap , what ever you do don´t use bleach or any other detergents

The brown ring is more than likely rust from the pot. , the dirt and water from the plant caused the rust to form
Rust is one of the most difficult stains to remove from marble, granite and other stone surfaces. Many of the rust removers available in stores can damage stone. You may want to give the following suggestion a try:
There is a product called “Iron Out” that is available from most home centers and hardware stores. This product is a white powder that is designed for removing iron from water softeners, but also works great for removing iron and other metal stains from stone. To remove iron stains mix 1 part “Iron Out” to 2 parts poultice powder (diatomaceous earth). Add water until you get a soupy consistency. Apply this mixture to the iron stain, cover with plastic and let it sit for 24 hours. After 24 hours remove the poultice and reapply if necessary.
As with any stone treatment it is always good practice to try this out on a small section of stone that is not visible to make sure it will not do any damage.

I think this going to be hard to do. I have tried everything on a stain on marble and can’t shift it. Tried bleach, tiny bit, lemon juice, all types of cleaner, but you have to be careful you don’t take the shine off the marble with the removers.

Marble is extremely porous. Once the stain is in it becomes part of the marbles features im afraid.
You should look to disguise the mark,perhaps replacing the plant pot.
Natural marble can be sealed to prevent further discolouration ,although I still would never rely on the sealer.