Cavolo nero, or black kale as its commonly known is the only thing I can think of from what you've said, not having seen the programme. I tried it about a month ago (bought from the veg section), gave me terrible heartburn - I didn't realise kale has fat in it.... but you might like it. Lots of health claims being made (superfood and all that) but its slightly less nutrient dense than watercress, spinach and chard, though still healthy. Still, makes a change if you like it...

I love it but it's sooo expensive. Loads of vitamins and iron in it.

Not as much iron as spinach actually, Cammomile, now they've checked - its full of nutrients, but spinach beats it on several other nutrient counts, though not by much. One of the highest iron content things is ordinary salad cress... as well as watercress.

If you're looking for something with high iron content, then look at parsley, which has more than twice that of spinach.