Looks like an Oil Seed Rape plant. Seed probably blown by the wind.

certainly one of the cabbage family, going by the substantial leaf and its size I wonder if it is a cabbage or sprout plant that has flowered. They flower in their second year. Is it flowering now? if yes than it's unlikely to be oil seed rape as they flower later april/may. also the leaves are more like a cabbage than oil seed rape.
could also be mustard, again a member of the cabbage family.

where abouts are you in the country, I only ask as it often helps answering questions? if you are in Norfolk it could well be mustard as it is a commercial crop there.

welcome to GoY :o)

At this time ofyear it could be mustard...but it could also be oil seed rape. The fields around here are just starting to flower.

It's actually in Cuba, the soil is dry where the plant started growing. My grandma said that another one like that started growing at her other house, but when she moved, it dried out. She is really curious and wants to know what kind of plant is it.

Based on my research and your answers, I think is a Florida broadleaf mustard plant. Which probably got there via a migrating bird dropping the seed. Thanks for your help :)

Well well...Cuba! Welcome to Goy and do keep posting, as we love to see what grows across the globe :)

wow that seems really early cottagekaren. the oil seed rape in the fields that back on to us and not showing any buds yet.

glad you have an id for it. if you go into your profile you can add where you are from and it will show as a flag under your avatar.

Yes, it always comes early here SBG...because of the south facing slopes and because we actually get a lot of sunshine here believe it or not. You'd never guess from the amount of complaining I do!