These are volunteer plants. This bed has not had New Zealand Spinach growing in it for THREE YEARS now. It is also coming up in my flower garden in places I never planted it. Go figure.
New Zealand Spinach is one of the few tropical spinach varieties that you can cook and it doesn't fall apart. It does prefer our winters to our summers and only volunteers in the late fall in SWFL.
Read my earlier post on this here: https://growagardener.blogspot.com/2016/02/new-zealand-spinach-how-to-grow-eat-and.html