Lettuce  

Lettuce is a leafy green that cuts across all classes and cuisines. You find it at the fast-food drive-through at the end of the exit ramp when you stop for a burger. It’s the bed of the salad that opens dinner at a tablecloth restaurant farther down the road.

It’s the most widely-grown, harvested and consumed foods in the U.S. It has become the most common salad green in the world, popular even in China.

Dozens of greens called “lettuce” are available but nearly all can fit into four basic categories: crisphead, butterhead, looseleaf and romaine.

Crisphead is round with tightly packed leaves. They’re thick and crunchy. They’re almost always a light green color, often with white streaks or patches. The most famous member of this group is Iceberg.

Butterhead, too, is basically round but not as compact. It has light green to lime green leaves, soft and tender, gathered in a loose rosette. Its category includes varieties called buttercrunch, Boston and bibb.

Romaine is tall and elongated, with stiff crispy leaves, sometimes thick, often very dark green. Most varieties have compact, tightly folded core at their centers called “hearts”. It’s often called “cos” and one of the most common varieties is Parris Island.

Looseleaf includes a wide range of varieties, and as its name implies, it’s a collection of flat or curled, spikey or rounded, short or long, floppy or stiff leaves. It comes in many colors, from light green to deep purple. Many types develop as a rosette.

In the past few years plant breeders have been developing new varieties that combine characteristics of two or three varieties into one lettuce. The trend has been prompted in part by the growing popularity of salad mixes and mesclun. Some of the new types have easy to cut, peel-off leaves. Some are big and robust while others are small “dwarfs”.

Breeders have also been working to create varieties that withstand both the colder and hotter conditions brought on by climate change.

Nearly all commercially-produced lettuce in the U.S. is grown in California, with about 70 percent of the annual crop, and in Arizona, with 30 percent. Long-term drought, however, threatens that dominance by western states.

Lettuce isn’t known as a “super food” but it has significant nutritional value.  Romaine, for example, has about 8 calories and 1 to 2 grams of carbohydrates per cup. It’s low in fiber, but high in minerals like calcium, phosphorous, magnesium and potassium. It's naturally low in sodium. It’s also loaded with vitamin C, vitamin K, and folate.

The most nutritious lettuce, though, are the types in the butterhead category.  The leaves are higher in folate, iron, and potassium than romaine, Iceberg or leaf lettuces.

Lettuce was originally farmed by the ancient Egyptians, who transformed it from a plant whose seeds were used to obtain oil into an important food crop raised for its succulent leaves and oil-rich seeds, according to Wikipedia.

It was adopted and adapted by the Greeks and then the Romans, who gave it the name “lactuca” for the white, natural latex fluid some varieties exude.

Europe and North America dominated the use of lettuce for centuries. It was first brought to the Western Hemisphere by Christopher Columbus.

By the end of the 20th century production and consumption had spread around the world. China now produces about 55 percent of all the lettuce used on Earth, according to United Nations statistics.