What Kind of Citrus Tree Has Thorns?
Several fruit trees, including many types of citrus fruit that flourish in U.S. Department of Agriculture plant hardiness zones 9 through 11, have thorns on their branches. The thorns are the tree's way of protecting itself against hungry animals that want to nibble on the leaves and fruit of the tree, which can heavily damage or even destroy a young tree. Over time, as the tree grows older and stronger -- and better able to handle animal damage -- the thorns usually diminish.
Lemon (Citrus limon) is the leading acidic citrus fruit, according to Purdue University Agriculture. Desirable for its distinctive odor and flavor, it is cultivated in tropical and subtropical climates around the world. Most true, or species, lemon trees have sharp thorns lining the twigs. Some hybrid varieties, however, are almost thornless, such as "Eureka," which is a leading cultivar in California.
Oranges (Citrus sinensis) are loved around the world for their attractive package and sweet flavor, although some are much sweeter than others. Over time, growers have bred oranges to be less thorny. Today, most varieties are either thornless or have thin, blunt, flexible thorns found only at the base of the leaves. Oranges that are bitter and not commonly consumed, however, may have large thorns. The hardy or trifoliate orange tree, for example, features sharp, 2-inch long thorns and sour fruit.
Limes (Citrus aurantifolia) are used in everything from cooking to adding fragrance to cleaners and other industrial products. They are the second most popular acidic citrus fruit -- second to lemons -- and are also less cold-hardy than lemons. Although lime trees, with their small, stocky profile and thorny branches, look rather tough, the fruit is actually sensitive to cold. Most commercially valuable lime trees do have small thorns, and although thornless varieties are more desirable, they are less productive, according to Texas A&M Aggie Horticulture. The Mexican lime, or the Key lime, is probably the most well-known of the varieties.
Grapefruit (Citrus X paradisi) trees, like other citrus trees, have thorns, but they are short and flexible, and they are only found on the twigs. "Marsh" is the most popular variety grown in the United States and is desirable for its sweet, juicy flesh and small number of seeds.
Kumquats (Fortunella spp.), included in the Citrus genus until 1915 when they were reclassified into the Fortunella genus, are prized for their sweet and tart flavor -- the thin, edible skin is sweet, but the pulp is tart. Kumquats are about the size of plums, with skin ranging from bright orange to ruby red, and are usually eaten whole. The trees are small, compact and slow-growing. Many, such as "Hong Kong," are liberally covered with thorns. A few others, such as the popular "Meiwa," are either thornless or feature small -- but still sturdy -- spines.
- Oecologia: Thorns as Induced Defenses -- Experimental Evidence
- Purdue University Agriculture: Lemon
- University of Arkansas Division of Agriculture: Plant of the Week -- Hardy Orange or Trifoliate Orange
- Texas A&M Aggie Horticulture: Texas Citrus and Subtropical Fruits -- Limes
- Purdue University Agriculture: Grapefruit
- Purdue University Agriculture: Orange
- University of Florida Environmental Horticulture: Citrus Spp.
- Purdue University Agriculture: Kumquat
- Pasco County Cooperative Extension Service: Get Aquainted With Kumquat