Citrus javanica Blume

Small, densely and irregularly branched, evergreen tree, about 5 m tall; twigs armed with short stiff sharp spines. Root suckers and suckers on older branches, characterized by stout sharp spines, are common. Lime in an everbrearing tree. Leaves alternate, elliptic to oblong-ovate, 4-8 cm x 2-5 cm, margin crenulate; petioles narrowly winged. Inflorescences short axillary racemes, 1-7(-10)-flowered; flowers small, white in bud; calyx cup-shaped, 4-6-lobed; petals 4-6, 8-12 mm long; stamens 20-25(-34), ovary 9-12(-15)-celled, style abruptly distinct. Fruit a globose to ovoid berry, 3-6 cm in diameter, sometimes with apical papillae, greenish-yellow; peel very thin, very densely glandular; segments with yellow-green pulp-vesicles, very acid, juicy and fragrant. Seeds small, plump, ovoid, pale, smooth with white embryos (polyembrionic). Limes hybridize freely with other Citrus species, and many hybrids are known, e.g. Lemonimes (lime x lemon), Limequats (lime x kumquat). Limes are divided horticulturally into acid and sweet limes. In addition to the common (Mexican, West Indian or Key) lime described, there is the Tahiti or Persian lime (2n = 3x = 27), presumably a hybrid of lime and citron (Citrus medica L.). It has a longer, globose fruit, acid but less richly flavoured than the common lime; the fruit is seedless or nearly so. The Tahiti lime is more hardy and successful in the subtropics; in South-East Asia it plays a very minor role. The sweet citron, probably from India, where it is of some importance. It has been used as a rootstock. Lime cultivars are not very distinct; in Thailand 'Kai' and 'Paan' can only be identified by fruit shape (ovoid and flattened/globose respectively).

Flowers are either perfect or male and borne in inflorescences of up to 10 flowers in the leaf axils of mature shoots, but are often single in the axils of a shoot which has just flushed. The stigma is receptive as the flower opens and remains so for a few days. Pollen is not released until the flower has opened. Copious secretion of nectar by a floral disk attracts insects, especially honey bees, which pollinate the flowers. Self pollination occurs but self-incompatibility limits fruit set. Fruit requires 5.5-6 months from flowering to harvest. In Thailand there is little fruit in March-April. This may be due to early ripening (colouring) of the fruit during the cool dry period of December-February. Alternatively, the gap in supplies may be caused by poor flowering or fruit set during September-October (the second half of the rainy season).

Limes can grow on poor soils and tolerate heavier soils than oranges, provided that good drainage prevents waterlogging.

The lime is at home in the lowland tropics. The tree is sensitive to cold but is quite drought-resistant. High incidence of bacterial canker is a limiting factor in the wet tropics; under dry conditions irrigation is necessary to obtain good quality fruits.

The lime is now cultivated throughout the tropics and in warm subtropical areas.

Unlike other citrus species, limes are rarely propagated by budding. In South-East Asia air layering is the normal method, elsewhere the trees are raised from seed. Sturdy twigs, preferably suckers, are selected for layering and the dust of coconut husk after fibre extraction is the medium used in Thailand. The layers are potted and nursed for 2-4 weeks before planting.

Husbandry: Unpruned trees have a dense twiggy canopy and crowded branches may die back due to competition. Hence, trees are pruned to thin the branches and to remove suckers and limbs infected by canker. To influence the harvest time, irrigation is withheld for 3 weeks in the dry season; resumption of irrigation triggers a flush which brings on flowering.

Diseases: Limes are susceptible to tristeza virus, but the more serious threat is bacterial canker (Xanthomonas campestris p.v. citri), which shortens the life of trees by gridling the trunk. The bacteria are distributed by rain. Strict orchard hygiene, i.e. removal of infested branches, spraying with copper early in the rainy season, and spraying with streptomycin are recommended. Pests: The obnoxious citrus leafminer (Phyllocnistis citrella) causes leaf malformation and early leaf fall. The pest affects almost every tree and to the extent that flowering is diminished. Control by insecticides is difficult because the caterpillars are relatively safe in their tunnels in the underside of the leaves, and the life cycles are short and overlap. Increased use of insecticides seems to have aggravated the pest, perhaps because predators are more vulnerable.

Other products: The fruit is used in nearly every home in South-East Asia, mainly to flavour food, but also to prepare drinks and for a variety of medicinal applications. Food: The rich flavour and acid taste make lime a favourite for hot and spicy dishes, either fresh or in the form of pickles and sauces. The refreshing qualities come to the fore in lime juice, lime tea and the use on other fruit, e.g. papaya. In Malaysia the fruit is preserved in brine and vinegar; it is enjoyed as an appetizer when fried in oil with sugar added. Medicine: The leaves and fruits have many medicinal uses, some of which are linked with the belief that limes drive evil spirits away.