Mustard greens
Excellent choice for greens. High in calcium, but somewhat high in goitrogens. Best when cut into larger pieces or strips. Finely chop or discard stems. Store cut, dried pieces in plastic storage bag with other greens wrapped in paper towels. Squeeze air out of bag.
Ca

2.4:1, Pro: 2.7%, Fat: 0.2%, Water: 91%, Fiber: 3.3%
STAPLE GREEN
http://www.greenigsociety.org/foodchart.htm
Anything that says staple can be for a gut load. Most of the leafy stuff can be dehydrated and frozen to be used as a powder.