From The Buffalo Seed Company:
 
"LETTUCE (Lactuca sativa) (leaves 50-60 days) — Merveille des Quatre Saisons is a French butterhead type heirloom lettuce that is absolutely delicious and can hold its own throughout the seasons. This is a great salad lettuce with crisp and tender leaves. Some plants have splashes of dark red colors against a nice green background while others are completely green."