Citrus trees are diverse evergreen trees and shrubs recognized for their aromatic flowers and flavorful fruits. While many popular citrus varieties cultivated today are largely thornless, thorns are a natural feature found across numerous species within the genus. These sharp appendages appear on branches and twigs. Understanding which citrus trees possess thorns and why can offer insight into their natural history and cultivation.
Common Thorned Citrus Varieties
Many citrus species exhibit prominent thorns. The trifoliate orange (Poncirus trifoliata), a close relative to true citrus, is notable for its very sharp, often 1 to 2-inch long spines and deciduous nature, unusual for citrus. This plant is frequently used as a rootstock for grafting other citrus varieties due to its hardiness.
Among the true citrus, several lime varieties are known for their significant thorns. Key lime (Citrus aurantifolia) trees can be quite thorny, with sharp projections that remain throughout the tree’s life, though they may shorten with maturity. Kaffir lime (Citrus hystrix), also called makrut lime, similarly features strong spines up to 1.5 inches long on its branches.
Lemon varieties also commonly display thorns, especially on younger trees or less domesticated types. Some common thorny lemons include Meyer lemon and Lisbon lemon, though thorniness can vary. Even if the upper part of a grafted citrus tree is thornless, the thorny rootstock might produce thorny suckers from below the graft union. These suckers should be removed to prevent the rootstock from dominating the desired fruit-producing variety.
The Purpose of Citrus Thorns
Citrus thorns serve as a defense mechanism, primarily protecting the tree from herbivores. These sharp structures deter browsing animals like deer from consuming leaves, young stems, or developing fruit. This protection is especially important for the survival of younger trees, as their foliage is more vulnerable to damage.
Thorns are often more pronounced on new growth and juvenile trees. As some citrus trees mature, the number or sharpness of their thorns can diminish. This ancient trait evolved to enhance survival against browsing animals. Over time, this trait has been selectively bred out of many commercially popular varieties for easier harvesting and handling.
Thorns and Citrus Cultivation
The presence of thorns on a citrus tree does not indicate that its fruit is inedible. Many delicious and widely consumed citrus varieties, such as Key limes and certain lemons, naturally have thorns. Thorniness can also vary within the same species due to factors like the tree’s age, specific cultivar, and growing conditions.
Gardeners often manage thorny citrus trees by pruning for safety, especially in high-traffic areas or where thorns might pose a risk during harvesting. Pruning thorns will not harm the tree. Thorns can sometimes serve as an identification clue for a particular variety or indicate the presence of a specific rootstock.