By Barbarak
North Yorkshire,
United Kingdom 
Wild flower I think but what? Strange thing. Last autumn I scattered seeds from an oriental poppy seed head over a small 2x2 foot square hoping some might germinate but instead in this area only there appeared seedlings but the true leaves didn't look like I was expecting . I dug them up and put into pots to see what came up . The photos show the uleaves and flowers. They are no where else in the garden.
1 May, 2017
Answers
Yup and the images are upside down :) I'd assume this is a weed and dispose of accordingly!
1 May, 2017
I think its oilseed rape - a seedling from a farm crop.
1 May, 2017
The leaves are wrong for rape. It could be Charlock, Sinapis arvensis, which is a common weed.
1 May, 2017
Aren't Charlock leaves longer than these though? Its not an easy family to sort out...
2 May, 2017
Sorry about upside down photos but always happens when photo taken on iPad and uploaded to this site. I ditched all the 'weeds' . I was curious as I hadn't seen it before locally or in my garden but I thought it would be a weed. Re the oriental poppy, do the seeds germinate easily?
2 May, 2017
Ignore this - couldn't delete it
2 May, 2017
I have oriental poppies appearing in profusion some years and only very sparsely in others. I have not sown them. I understand poppy seed can lay dormant for many years and pop up when the ground is disturbed. (If they feel like it!)
2 May, 2017
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Whatever it is, it's a member of the Mustard family.
1 May, 2017