[PennyS]

 It is now growing well.

If it is horseradish, it will grow exceptionally well - it can be quite invasive!! 

[Sideways]

Sideways, is the plant in the photo outside in the open or is it covered .

Its growing outside, no protection. There are several more plants to the right of the image, considering how early/chilly it is Im expecting quite a crop, hence my keeness to identify it and eat it all!

[Sideways]

BTW - why did you plant up a bag of unknown cuttings? Are you sure that there wasn't any Japanese knotweed in there too 

I thought I knew them all but lost track of this one...

[Sideways]

Is it a type of rocket?is there a prize for getting it right,like an Easter egg?

You get to feel smug for a day! 

[Spana]

It looks like American Cress/ Land Cress, but never heard of it being grown from tubers.

[Flump]

ok,I can cope with that....oh wait,no chocolate? :blink:
 If you crush the leaves,do they have a smell?

[gillie]

It is not a chicory or endive is it?

Gillie

[Aunt Sally]

Actually looks more like cornsalad (lambs lettuce) to me although that is usually grown from seed

I've only ever grown it from seed.  I wouldn't have any idea what the roots would be like.

[Aunt Sally]

My lamb's lettuce had just round leaves though.  Worzel (who dug the bed over) said there were no large roots.

[Puenktchen]

It is definitely no lambs lettuce. We are eating it at the moment fresh from our allotment and they have only rounded leaves, no incised leaves like the plant on the picture. For me, it looks also more like a Knautia arvensis/field scabiosa or something similar.

[paintedlady]

It's not "land cress" is it?  http://www.thompson-morgan.com/seeds1/product/616/2/ 

[Puenktchen]

The leaves look different, landcress has more rounded leaves, the leaves of the unknown plant are more pointed. I am really curious now about the real name of the plant.

[plum crumble]

maybe send a pic to the RHS? - they should identify it for you

[Sideways]

Im still waiting for a reply from the person who gave it to me, Im pretty sure Ive got the right person.

If this fails I will do as PC suggests and send it in to the RHS.

Im glad so many of you are interested too!

[Bagpuss]

It is definitely no lambs lettuce. We are eating it at the moment fresh from our allotment and they have only rounded leaves, no incised leaves like the plant on the picture. For me, it looks also more like a Knautia arvensis/field scabiosa or something similar.

Ah okay I wasnt sure what the leaves looked like before it ran to seed as it is many years since I grew it