I am from the south of mexico, and am not sure what is this, the stem looks like plastic, the pot had like 10 different seeds before, or maybe is just a weird weed I have to cut?
It looks like "Pilea pumila" commonly known as clearweed. It is a member of the nettle family (Urticaceae) and has a broad native range in North America. It is usually thought of as a weed, but apparently Native Americans once used in for medicinal purposes. There are many links online about it. Here are two of them.