spread to tropical and subtropical North America, including Mexico, Florida, and later California. In California in the late 19th century, "Mexican" limes were more highly valued than lemons; however, in Florida, they were generally considered weeds. Then, in 1894–95, the Great Freeze destroyed the Florida lemon groves, and farmers replanted Mexican limes instead; they soon became known as the Florida Key Lime, a "beloved regional crop". But when the 1926 Miami hurricane ripped them up, they were replanted with the hardier, thornless Persian limes. Since the North American Free Trade Agreement came into effect, most Key limes on the United States market have been grown in Mexico, Central America and South America. They are also grown in Texas, Florida, and California. The Key lime has given rise to several other lime varieties. The best known, the triploid progeny of a Key lime-lemon cross, is the Persian lime (Citrus × latifolia), the most widely produced lime, globally. Others are, like their parent, classed within C. aurantiifolia. Backcrossing with citron has produced a distinct group of triploid limes that are also of commercial value to a limited degree, the seedy Tanepeo, Coppenrath, Ambilobe and Mohtasseb lime varieties as well as the Madagascar lemon. Hybridization with a mandarin-pomelo cross similar to the oranges has produced the Kirk lime. The New Caledonia and Kaghzi limes appear to have resulted from an F2 Key lime self-pollination, while a spontaneous genomic duplication gave us the tetraploid Giant Key lime. The potential to produce a wider variety of lime hybrids from the Key lime due to its tendency to form diploid gametes may reduce the disease risk presented by the limited diversity of the current commercial limes. Agronomy Cultivation and propagation There are various approaches to the cultivation of Key limes. This variety of citrus can be propagated from seed and will grow true to the parent. The seeds must be kept moist until they can be planted, as they will not germinate if allowed to dry out. If the plants are propagated from seed, the seeds should be stored at least 5–6 months before planting. Alternatively, vegetative propagation from cuttings or by air layering may permit fruit production within one year, and from genetically more predictable lines of plants. Another method, digging around a mature tree to sever roots, will encourage new sprouts that can be transplanted to another location. Clones are often bud grafted into