Among more exotic varieties of greens, mustard spinach, water spinach (with slender, pointed leaves), and chrysanthemum greens (all Asian, the latter an edible kin to the familiar floral type) are tender enough to mix raw in salads or use as last-minute additions to stir-fries or soups.
Mizuna (Japanese mustard greens) have sawtooth leaves and a mustard tang used to accent mesclun mix or soup.
Tatsoi (Chinese flat cabbage or spinach mustard) is kin to bok choy, with spoon-shaped leaves and a spinachlike flavor. It withstands freezing temperatures, and can be harvested even under snow.