Spineless Prickly Pear Cactus pads (Opuntia).
Can be bought at grocery stores fresh in the produce section as Nopal or Nopalitos. The fruit, known as Tunas is also good.
Collard Greens are the best and most preferred leafy green...along with Romaine, Escarole, Endive, Arugula, and Dandelion greens.
Squash (Yellow, Butternut, others) is also a good choice.
That's a start.
jsc
-----
"As hard as I've tried, just can't NOT do this"
John Crickmer