Collard greens

Measured by kg; no spoon or counted-piece conversion is needed.

Instead of Collard greens

Mustard greens
Use the same weight, strip tough stalks and shred. They have a similar bite; cook until tender, checking a little earlier than collard greens.
Spinach
Use the same weight, wash well and add later. It wilts and cooks much faster, gives a milder taste and releases more water.
Amaranth leaves
Use the same weight, pick leaves and tender stems. Add near the end; they are softer and cook in a few minutes.