See page 215-216 of Seed to Seed by Suzanne Ashworth.
New Zealand Spinach is the only member of it's family! There are only 3 types of New Zealand Spinach, so if you only grow one, you don't have to do anything to keep the seed pure. It likes the heat, not the cold, so it will grow when other spinach bolts. You'll want to eat this one cooked, it has a bitter taste if eaten raw. It reseeds itself, so that makes it kind of invasive, make sure you contain it!
Please read the description in Seed to Seed, and let me know when you come across or plant something interesting.