Clementines:
Clementines are a darkly colored variety of mandarin, or tangerine, popular in the American Southwest, from Texas to California. Small and thin skinned, they are easy to peel, have few or no seeds and separate easily into segments. Perfect for snacking out of hand or as an addition to green or fruit salads. Clementines originated in Algeria around 1900 CE and were brought to the United States shortly thereafter. The season runs from November through January.

Common Sweet Oranges:
Valencia is the most important and ubiquitous variety of many in this category. Primarily used for juice, sweet oranges have a mild flavor that is often augmented during the commercial juicing process with peel oils. They can be eaten out of hand but are more difficult to peel and segment than navel oranges. The season for Valencias runs from March through June with other varieties filling out the calendar year.

Grapefruits:
Grapefruit (Citrus paradisi) is the most recent offspring of the Citrus family - a family prone to hybridization - appearing in the West Indies in the 18th century. A cross between the sweet orange and pomelo, grapefruit is a large, round citrus fruit with a somewhat bitter flavor that is an acquired taste for some. Its assertive flavor recommends it as a dessert fruit rather than one for cooking. Difficult to peel, it is often halved and eaten with a spoon. Globally, about half the grapefruit crop is used for juice. A milder flavored pink variety appeared in 1913. Grapefruit is available year round but supply peaks in January.

Key Limes:
Also called West Indian or Mexican lime (Citrus aurantifolia), this small, yellow-green fruit is the original or true lime and the most acidic of all citrus fruits. It is the dominant variety everywhere except North America. It can be squeezed over green salads, in ice water, atop seafood soups and fish dishes and of course, in Key lime pie. Available year round with supply peaking June through August.

Lemons:
Lemons are perhaps the most versatile citrus fruit and certainly the most important for cooking, having been used as an accompaniment for fish and seafood for centuries; as a souring agent; a crucial ingredient in sweet dishes such as meringue and chiffon pies, mousses and soufflés; a source of both flavor and pectin in jams and jellies; a delicate substitute for vinegar in salad dressings; a flavor enhancer for tropical fruits like guava and papaya and, of course, lemonade. Lemons are available year round with the U.S. fifth in production behind India, Argentina, Spain and Iran.

Mandarin Tangerines:
Also known as tangerines in the U.S., mandarins (Citrus reticulata) are smaller, flatter and have less acid than oranges. Their delicate flavor is lost in cooking so mandarins are usually eaten fresh. They are typically more darkly colored than oranges, with looser skins that peel and segment easily. Available November through spring.

Navel Oranges:
Easily peeled and seedless, navel oranges (a member of the Citrus sinensis species) are the best choice for eating fresh. They are distinguished from other oranges by a navel-like depression on the blossom end, beneath which is a miniature set of segments. Juice squeezed from navel oranges becomes very bitter within minutes due to a compound called limonin. Navel oranges originated in China and are now cultivated in subtropical areas worldwide. The season runs from late October through April in the U.S., with the best quality oranges available in mid-season, December to February.

Tangelos:
Tangelos are a cross between mandarins and pomelos or mandarins and grapefruit. The best known varieties in the U.S. are Minneola, with a rich, sharp flavor and distinctive pronounced knob on the stem end, and Orlando, a pale orange fruit with a mild flavor. Its juice is well suited to salad dressings and sauces for meats. Available January through March.