I've grown Chenopodium giganteum, a variety of Tree Spinach that thrives in the UK producing 7ft tall plants. Please look at this article on Wikipedia:
http://en.wikipedia.org/wiki/Chenopodium_giganteumIt grows as a small bush if you crop the tender shoots when the plants grow to about 2ft: they are really, really delicious if chopped fine and sweated in a pan with a bit of oil, garlic, onion, salt, pepper. It really is the most delicious green you can grow and the most nutritious too. When young it tastes like a cross between well cooked Kale, Spinach (as a Chonopodium, it is related) with a faint Asparagus aftertaste.
Also, it is supremely productive - not only do you get massive plants on any patch of clear land, you also get thousands of seeds for the following year from every tree at the end of the season which is late October. Like many plants, if eaten after the plant has flowered, it's too late and the flavour will have fled.
This is an amazing, nutritious, delicious, green leafy vegetable plant and I highly recommend growing and eating it.
