Calories in Lettuce, cos or romaine

What makes lettuce so powerful?

Romaine lettuce, scientifically classified as Lactuca sativa var. longifolia, forms distinct, elongated heads that grow upright rather than spreading outward. This vertical growth habit creates a natural self-blanching effect: the outer leaves are exposed to intense sunlight, while the tightly packed inner leaves remain shielded, developing their characteristic pale, crisp texture. Because of this structural adaptation, the nutritional profile varies dramatically between the outer and inner leaves. The dark green exterior leaves perform the majority of the plant's photosynthesis, accumulating significantly higher concentrations of beta-carotene, lutein, and vitamin K compared to the pale yellow-white interior ribs. Historically, this lettuce variety traces back to the Mediterranean, specifically the Greek island of Kos, which gave it its alternate name, 'cos lettuce.' It later became a staple in Roman gardens, eventually earning the name 'romaine' from its association with the Roman papal gardens in France. Unlike iceberg lettuce, which was bred specifically for storage and transport, romaine retains much of the phytonutrient density of its wild ancestors, making it one of the most nutritionally dense lettuces available.