Here we may be dealing with different names - British/American.
Perpetual Spinach seems to be called Spinach Beet by British seed company, Thompson Morgan.
http://www.tmseeds.com/product/697.html
I really like it, it tastes more like beets than anything else but is closely related to chard. It is a biennial so usually provides fresh greens right thru the season.
New Zealand spinach (you suppose they call it something else in New Zealand?

) is a perennial. Once you've got it, you generally have got it. It spreads and if it doesn't make enuf growth its first year, it'll be back like a carpet the 2nd year.
Dad grew it and I liked it but he didn't and took it out. I guess I could have taken a start before he did.
"Iron-y taste," huh? No, I think I would have dis-remembered that variety.
I live where it will turn hot and dry in about an instant. Regular spinach is difficult to grow. The varieties I have the best luck with are Hector and Unipack 51. How are those for unappealing names?? I mean, you could go with "Medania" or "Melody" . . . I'm stuck with Hector and Unipack 51

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Steve