Problem with black bamboo

A few months ago I was given some black bamboo cuttings, which pleased me as I'd tried growing some from seed and out of 100 seeds, only two germinated.
Anyway, since then both the plants from cuttings and the two from seeds have grown rapidly and all are over 2 ft tall but their leaves are kind of deformed. They're over-sized, wrinkly and curly but not brown. I can't figure out if they're under-watered, over-watered or suffering from something else as no pictures I have found on the net show leaves the same as these.
Any help and/or suggestions would be greatly appreciated.
PS: the only reason the stem is drooping on this pic is it needs a taller stake to tie it to, which I'll be doing tomorrow. The other plants have the same leaf problem but their stems are straight and healthy.

Thanks in advance.
Posts
I had considered that also but the two I grew from seed look the same and those were ordered as black bamboo and labelled as such when I got them.
I do have a Red bamboo which I bought as a plant online and that is perfectly healthy. I have no idea what's going on.
I have to agree that this is definitely not bamboo. Bamboos are monocots which means that they have parallel leaf veins (along with grasses, tulips, lilies etc.). This plant has leaves with a central midrib and branching veins confirming that it is a dicot. To me, it looks like some form of dock, sorrel or another member of the Rumex genus.
I've been having trouble with mine also. It had a lovely yellow flower and now this has happened!
Sorry, couldn't resist it! But joking aside you have to be careful who you buy seeds or young plants from. Some of the more established suppliers are bad enough and I would be wary of the likes of e-bay unless they have some good feedback.
Must go, I have some magic beans to plant!
Thanks for your help, guys. Much appreciated.
As others have said, that definitely ain't bamboo. It looks more like one of the weeds with which I do regular battle in the garden.
I don't think bamboo grows from cuttings, you need a bit of root with a shoot or potential shoot. Also interested to know the origin of the bamboo seed.
In the sticks near Peterborough
That's very kind of you, Tetley. I really appreciate it. However, as I have one good Red bamboo plant, I'm going to split that so instead of my original plan of alternating down the fence with red and black bamboo, I'll just stick with red all the way down. Hopefully the effect will be just as good.