Lettuce

Lettuce is a temperate annual plant most often grown as a leaf vegetable. In Western countries, it is typically eaten cold and raw, in salads, hamburgers, tacos, and several other dishes. In some places, including China, lettuce is typically eaten cooked, and use of the stem is as important as use of the leaf.

A lettuce plant has a short stem initially (a rosette growth habit), but when it blooms, the stem lengthens and branches, and it produces many flower heads that look like those of dandelions, but smaller. This is called bolting. When grown to eat, lettuce is harvested before it bolts.

Commonly recognized types of lettuce include:

Iceberg lettuces form tight, dense heads that resemble cabbage. They are generally the mildest of the lettuces, valued more for their crunchy texture than for flavor. Varieties of iceberg lettuce are the most familiar lettuces in the USA. The name Iceberg comes from the way the lettuce was transported in the US in the 1930s. It was transported on trainwagons all covered in crushed ice - making it look like icebergs.

Crisphead lettuces form moderately dense heads with a crunchy texture; this type is intermediate between iceberg and looseleaf types.

Looseleaf

Romaine, also called cos is a head-forming type with elongated leaves.

Butterhead, also called Boston or bibb forms loose heads; it has a buttery texture.

Batavia is similar to butterhead.

Chinese lettuce types generally have long, sword-shaped, non-head-forming leaves, with a more bitter and robust flavor than Western types, appropriate for use in stir-fried dishes and stews.

There are hundreds of varieties of lettuce within these categories.

Some lettuces (especially iceberg) have been specifically bred to remove the bitterness from their leaves. These lettuces have a high water content with very little nutrient value. The more bitter lettuces and the ones with pigmented leaves contain antioxidants.