What is this chinese veg., and how to cook it?

At the Asian market I bought a green vegetable that I thought was labelled Chinese spinach (though I wouldn't swear to it). It had comparatively tough stalks--long, thin, but tough, almost woody--with leaves on them. I figured I'd slice it and stir-fry it.

It was quite tough to cut, and when I stir fried it, the leaves came out fine, but the stalks were inedible. We decided the entire dish was inedible and a disaster.

Can someone tell me what vegetable this was, and how are you supposed to cook it?