I´m sorry but could anyone please help me and tell me what kind of plant this is? It suddenly started growing in one of the pots of my other plants

Welcome to ATP!

It looks like a dandelion. The seeds float in the slightest breeze and come to earth whenever they spot dirt.

Daisy

Oh really? How nice!

looks like some type of thistle maybe w the prickly ends on the leaves. Really hard to tell, a closer pic of the leaves would be nice. The leaves appear from the photo to be bluish tinted and to be kind of a heavy substance? It does not appear to be a dandelion to me. dandelions are very green and the flesh of the leaves is somewhat thin.

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Thicker fleshy substance of the leaves with a bluish tint could suggest a Brassica Family , mustard , cabbage , Kale , etc , the list is huge ,

that is what I was thinking too, but unless it is a seed he planted, most likely a volunteer weed thus my thistle guess... It does look alot like kale to me.

Frillylilly Wild Mustard or cabbage (spinach?) are actually invasive self sowers in more western parts of North America .
Several Mustard members are self sowers here ,
Your correct with several of the smaller thistle are that shape , and look also
This is more probable ,grow it until it blooms ,,

SandFlytrap, it would be good to know where you live. It would make an ID easier.

Daisy

I think I agree will Daisyl. It look just like a Dandelion, a weed.

Hi & welcome! It looks like it may be a Sonchus, but IDK which one.