Boston or Bibb is a delicious head lettuce with a softer and more buttery texture than iceberg. Its loose, succulent, almost oily leaves are green or brown-red on the outside, creamy white on the inside. Kale and Collards are basically cabbages without heads. They have a milder flavor than head cabbage though. Kale is usually flat with frilled leaf edges or very curly like parsley.
Collards have large flat dark green leaves.
They are among the most nutritious of the greens and are great cooked. Watercress is a popular salad green with dark green small leaves and a peppery taste. Leaf Lettuce is sold either as a loose head or as young leaves in a mesclun mix. The leaves may be waxy with curly margins, or flat and deeply lobed like an oak leaf, or even frilly. These come in red and green.