The original is the "true" lime, Citrus aurantifolia, native to northeastern India and Southeast Asia and known here as Mexican, Key or West Indian limes. All are small, roundish, seedy and sour, with pale greenish flesh; they are usually sold with green rinds, although in cool-winter climates like ours they turn yellow when fully ripe. They are prized for their acidic juice and rich aroma, with pine, spicy and floral notes.
This distinctive aroma, which is more pronounced in true limes than in their more common large-fruited cousins, represents a happy combination of its pollen parent, citron, the father of the lemon, and its seed parent, a papeda, possibly C. micrantha, one of a group of primitive citrus species with acrid rind oil, like the Kaffir lime.
The local season for true limes, roughly October to December, is earlier and shorter than that for large-fruited limes. In general, it's earlier and shorter still in inland districts with more extreme climates and later and longer in coastal areas, where small quantities may be available year-round. True limes produce most heavily in tropical climates and are the most cold-tender of citrus, so all but a tiny fraction of them are imported, mostly from Mexico. Because of their small size and thin skin, true limes dry out easily and are relatively perishable, so they're less common and more expensive per pound than large-fruited limes.
Large-fruited limes — the Bearss variety in California, and Tahiti or Persian elsewhere — are by far the most common type of limes here, both at supermarkets and farmers markets. The local season runs from late summer to early spring, so we're right in the middle now, although individual groves can differ markedly in timing.
Historically the large-fruited limes were accorded their own species, C. latifolia, but scientists now understand that they represent a natural hybrid of true lime and citron. Unlike most kinds of citrus, which have two sets of chromosomes, large-fruited limes have three, and this genetic peculiarity causes them to be sterile and therefore seedless. This and their larger size makes them more convenient than small-fruited limes, although at their best the latter arguably have a slight edge in aroma.
The more important factor is ripeness: Although Mexico can grow very good Persian limes, producers there sometimes harvest the fruit when it is dark green and dry, so we're fortunate to have access at farmers markets to light green, silver (intermediate) and yellow limes, which are juicier and more aromatic.
I'm still surprised every year when I see the canary-yellow color of fully ripe Bearss limes from inland producers like Pritchett Farms of Visalia, which seem more like Meyer lemons until you scratch and sniff the rinds or cut them open to reveal the pale greenish flesh.
Demand from immigrants from tropical Asia and Latin America, and an increasing taste among native-born Americans for tropical cuisines and food habits, has spurred a continuing boom in lime imports. While per capita consumption of citrus overall declined 24% from 1999 to 2009, consumption of limes more than doubled, from 1.55 to 3.61 pounds, according to Department of Agriculture statistics.
The vast majority is imported from Mexico, where huanglongbing, a bacterial disease deadly to citrus trees, has spread rapidly since its discovery in 2009, and threatens to severely disrupt production. Florida, which used to be the leading domestic source of limes, has lost almost all its groves — its famous Key limes and its large-fruited varieties — to hurricanes and disease. California's lime acreage, which was 473 in 2010, has remained stable for the last decade, leaving our area as the last significant domestic source.
Those are the two most important types of limes, historically and commercially, but the name has also been applied more loosely to other citrus with some (but not necessarily all) lime-like features such as small size, green color and acid pulp. These differ in ancestry, although some share common parents with the limes proper.
The most widely available exotic type, sweet lime (C. limettioides), is a hybrid of citron and either sweet or sour orange, small to medium in size, roundish, with a prominent nipple, yellow rind when ripe and pale yellow pulp. It is almost completely lacking in acidity, giving it a flavor that seems insipid to most Americans, but sweet limes (sometimes called sweet lemons) are very much appreciated in areas such as Latin America and the Middle East, where they are considered to be refreshing and healthy.
The Kaffir lime, from a species (C. hystrix) related to the papeda parent of true limes, is native to Southeastern Asia, where the highly aromatic leaves are indispensable in Thai cooking. The fruits, round with a nob at the top and a bumpy rind, are bitter and seedy, and are often left by growers to fall on the ground. In their native counties, they are commonly used in hair wash and insect repellant, although the juice and grated rind are occasionally used in cooking.
The finger lime, Microcitrus australasica, looks quite different from other citrus, like a gherkin, up to 3 inches in length, with thin skin and round, firm juice vesicles that pop on the tongue like caviar. It has a flavor that combines lemon and lime with green and herbaceous notes, and has been a novelty and high-priced sensation in the last several years as the first local plantings have started bearing fruit. Peak season is October to December, but the trees produce some fruit year-round in coastal districts. Finger lime caviar is used with seafood, cocktails and desserts, and it adds a welcome acidity and crunchy texture to Fuyu persimmons, also at their best at this time.
My pick for a coming foodie craze, but still currently the least familiar of exotic limes, is Rangpur lime (C. limonia), which looks just like a mandarin, medium in size, flattish and seedy, with orange skin and flesh. If you taste the very tart pulp, however, you'll know immediately why it is sometimes called "mandarin lime." Native to the Indian subcontinent, it's a hybrid of citron and mandarin, backcrossed to mandarin. The Rangpur's rind and juice have a clean, spicy flavor, which makes it a favorite of adventurous citrus lovers for marmalade and cocktails.
Sandy Lejeune, who used to work at Fairview Gardens, now tends an orchard that has a few Rangpur lime trees, and he sells the fruits at the Santa Barbara Saturday farmers market. Mud Creek Ranch of Santa Paula has planted Rangpur trees, although they're still young. A specialty citrus grower in Orange Cove, Rising C Ranches, sells Rangpur limes by mail order from late December to March.