As stated in http://www.gov.pe.ca/af/agweb/index.php3?number=70431, there are 5 types of lettuce: • Crisphead (also called Iceberg lettuce) • Butterhead • Cos or Romaine • Loose leaf or bunching and • Stem lettuce (also called Asparagus lettuce or Chinese lettuce/ celtuce).
hope that'll help too =)