Citrus: Lemon, Lime, Orange, Tangerine,
Grapefruit - Citrus spp.
The genus Citrus
belongs to the Rutaceae or Rue family, sub-family Aurantoideae. While Citrus is by far the
most economically important genus, two other genera contain species
important in citriculture:
1. Fortunella spp.
(Kumquats). Originally classified with citrus, kumquats were then moved
to their own genus, named after Robert Fortune, who introduced kumquats
to Europe. They are evergreen shrubs or small trees (8-15 ft), native
to southern China, but can be grown around the world into subtropical
areas. Unlike citrus fruits, the peel of the fruit is
edible, and usually sweeter than the pulp. Four major cultivars were given species status by
Swingle, a noted citrus taxonomist:
'Nagami' - F. margarita Swing. Also called
Oval or Long Kumquat. Fruits are longer than wide, 1-1 ½" long,
with thin, yellow-orange peel.
'Meiwa', or Large Round Kumquat
- F. crassifolia Swing.
Possibly a hybrid between 'Nagami' and 'Marumi'. Round fruit, thick
'Hong Kong', or 'Hong Kong Wild'
- F. hindsii Swing. Fruit is
orange/scarlet when ripe, many seeds.
'Marumi' - F. japonica Swing. (syn. Citrus madurensis Lour.). Also
called round kumquat. Thin, golden-yellow peel surrounds aromatic and
trifoliata L. Raf. - trifoliate orange. Important as a
rootstock for citrus, especially in Japan, although the fruit is
scarcely edible. It is used as a male parent in production of citrange
(sweet orange* trifoliate orange) rootstocks, and as an ornamental. It
has a deciduous habit in cooler areas, and can tolerate more freezing
than any other citrus relative. It is native to northern China, and
grown as far north as Philadelphia in the eastern USA.
The 5 commercially important fruit crops (sweet orange,
tangerine, grapefruit, lemon, and lime) are recognized as single
species within Citrus:
(L.) Osb. - Sweet oranges. This is a widely accepted name for this
crop, containing 4 groups of cultivars: common oranges, blood oranges,
navel oranges, and acidless oranges (see below). The term "orange" is
used rather loosely, sometimes for fruits that look like oranges but
are not C. sinensis. Examples include: 'Temple' and ‘Page' oranges (
tangerine hybrids), Satsuma orange (a cold hardy variant of tangerine),
and Trifoliate orange (Poncirus
Blanco - Tangerine, mandarin, or satsuma. Due to the success of
breeding with these types, many
cultivars and hybrids have been produced or formed naturally, some
erroneously given species status. I prefer to use C. reticulata for all tangerines,
but other species names sometimes given in the literature include: C. unshiu (Satsuma), C. deliciosa (Willowleaf), C. reshni (Cleopatra), C. nobilis (King), and C. temple (Temple).
Macf. - Grapefruit. This is clearly not a true species, but its
economic importance today has granted species status that even a lumper
could not deny. Grapefruit is thought to be a hybrid of pummelo and
sweet orange that occurred naturally somewhere in the Caribbean between
the time of Columbus' voyages and its introduction to Florida in 1809.
Burm. f. - Lemons. I would lump the rough lemon (C. jambhiri), sweet lemon (C. limetta), and Volkamer lemon (C. volkameriana) as variants within
C. aurantifolia L.
- Limes. The literature distinguishes the two main cultivars - 'Key'
and 'Tahiti' - as separate species, with the latter labeled C. latifolia Tanaka or Citrus X tahiti Campbell. I would
lump these two, along with the 'Rangpur' lime (C. limonia) and sweet limes (C. limettioides), all under C. aurantifolia.
Three other citrus fruits given species status and worthy of mention include:
C. grandis (L.)
Osb. or C. maxima (Burm.)
Merr. - Pummelo or shaddock. This species originates from southeast
Asia where it is as common as grapefruit is in the USA. It is much
larger and thicker-peeled than grapefruit, but said to have milder
L. - Sour orange. This is allied with limes by some, but is a very
important rootstock and ornamental. Cultivars and
variants include: Bittersweet, Oklawaha, Vermillion Globe, Paraguay,
Trabut, var. myrtifolia
(Myrtle), Bergamot, daidai (Japanese), Leaf of Chinnoto, and C. taiwanica Tanaka.
medica L. - Citron. This lemon-like fruit may be the progenitor
species of modern lemons and limes. The peel is very thick, and the
white, spongy portion of the peel is edible.
Two citrus fruits of minor importance are the pummelo or
shaddock (left), and the citron (right).
Several hybrids among Citrus
species, and between Citrus and
Poncirus or Fortunella, have been produced
either naturally or through controlled breeding. A series of prefixes
and suffixes is used to denote the parents of such hybrids:
Citrange (trifoliate orange x
Citrumelo (trifoliate orange x
Tangor (sweet orange x tangerine)
Tangelo (tangerine x grapefruit)
Sweet Orange. Cultivars are
subdivided into 4 groups based on fruit characteristics:
Tangerine. Like sweet oranges,
tangerine cultivars fall into 4 main groups:
- Common or round oranges
- Blood oranges
- Acidless oranges
Grapefruit. The major
white-fleshed cultivars are ‘Duncan' and ‘Marsh'; the former is seedy
and the latter seedless. 'Thompson' (syn. 'Pink Marsh') was a mutation of ‘Marsh' with pink
flesh, and is also seedless. Other deep red cultivars include ‘Star Ruby', ‘Ruby
Red', ‘Rio Red', and ‘Flame', grown largely in Texas.
- Mediterranean or ‘Willowleaf'
- Hybrids. Crosses of tangerine with
orange (tangors) or grapefruit (tangelos) have produced many
cultivars of importance in the USA.
Limes. ‘Key' (syn. ‘Mexican',
‘West Indian') and ‘Tahiti' (syn. Persian) are the major cultivars.
‘Key' limes are small, round, and seedy, and turn yellow under
Mediterranean conditions. ‘Tahiti' limes are larger, green, and shaped
Lemons. The main cultivars are
'Lisbon' (oval to round, more pronounced stylar end furrow and point)
and 'Eureka' (oval, less pronounced stylar end). 'Meyer' is a cold hardy, larger
fruited cultivar used as an ornamental or containerized plant, and is
probably a lemon hybrid. ‘Femminello' and ‘Verna' are the major
cultivars in Italy and Spain, respectively.
The two major lime cultivars are ‘Key' and ‘Tahiti', the
former being small, round, and seedy, and the latter larger, oval, and
seedless (left). ‘Lisbon' lemon is the most common lemon in the USA
HISTORY OF CULTIVATION
The center of diversity for Citrus ranges from northeastern
India eastward through the Malay archipelago and south to Australia.
Sweet oranges probably arose in India, the trifoliate orange and
mandarin in China, and acid citrus types in Malaysia. Oranges and
pummelos were mentioned in Chinese literature in 2400 BC, and later in
Sanskrit writings (800 BC) lemons were mentioned. Theophrastus, the
Father of Botany, gave a taxonomic description of the citron in 310 BC,
classifying it with apple as Malus
medica or Malus persicum.
At the time of Christ and shortly thereafter, the term "citrus" arose
as a mispronunciation of either the Greek word for cedar cones,
"Kedros", or "Callistris", the name for the sandalwood tree.
At this time, citrus fruits were spread throughout
Asia, North Africa, and Europe along trade routes. The dissemination
was carried out by many cultures, indicating widespread appeal of the
fruits at this time. From the first centuries BC to medieval times,
orangeries and citrus "groves" were established in Europe, and
cultivation became more sophisticated. Christopher Columbus, Ponce de
Leon, and Juan de Grijavla carried various citrus fruits to the new
world in the late 1400's early 1500's. Citrus culture proliferated in
Florida in the late 1700's, when the first commercial shipments were
made. Right about this time, citrus was introduced to California,
although it was much later that commercial production began in the
west. With the advent of large-scale irrigation projects in the 1940's,
citrus culture increased greatly in western states. Today, citrus
fruits are grown commercially in Florida, California, Arizona, and
World (2002 FAO) - 64,128,523
MT or 141 billion pounds. Oranges are produced commercially in 114
countries worldwide, on about 9 million acres. Worldwide average yields are just over
|Top 10 Countries
(% of world production)
|1. Brazil (29%)
||6. Spain (4%)
|2. USA (18%)
||7. Italy (3%)
|3. Mexico (6%)
||8. Iran (3%)
|4. China (6%)
||9. Egypt (3%)
|5. India (5%)
||10. Pakistan (2%)
United States (2002 USDA) -
11,403,136 MT or 25 billion pounds. Production has increased 1.5%
per year in last decade. The industry value is $1.8 billion. Leading
1. Florida (82%)
2. California (16%)
Prices received by growers are among the lowest of any fruit
crop in the USA: 5-15 ¢/lb, with fresh fruit receiving 10-15
¢/lb, and processed about 5-6 ¢/lb.
World (2002 FAO) - 4,979,781
MT or 10.9 billion pounds. FAO statistics include pummelo with
grapefruit, so a small fraction of this amount is actually not
grapefruit. Produced commercially in 74 countries worldwide, on about
653,000 acres. Yields average 16,700 lbs/acre.
|Top 10 Countries
(% of world production)
|1. USA (44%)
|6. Israel (5%)
|2. China (7%)
|7. Argentina (3%)
|3. South Africa (6%)
||8. Turkey (3%)
|4. Cuba (6%)
||9. India (3%)
|5. Mexico (5%)
||10. Tunisia (1%)
United States (2002 USDA) -
2,206,464 MT or 4.8 billion pounds. The industry value is $285
million. Yields range from about 8000 lbs/acre in Arizona to 38,000
lbs/acre in Florida. Prices received by growers are extremely low,
about 5 ¢/lb. Leading states:
1. Florida (83%)
2. Texas (10%)
3. California (8%)
4. Arizona (<1%)
Hybrids [hybrids include tangelos and tangors. FAO statistics
may place some hybrids in an alternate category, "Citrus NES", so these
data may be a slight underestimate]
World (2002 FAO) - 18,792,909
MT or 41.3 billion pounds. Produced commercially in 60 countries
worldwide, on about 4.2 million acres. Worldwide average yields are
|Top 10 Countries
(% of world production)
|1. China (38%)
||6. Iran (4%)
|2. Spain (10%)
||7. Thailand (3%)
|3. Japan (7%)
||8. Italy (3%)
|4. Brazil (5%)
||9. USA (3%)
|5. South Korea (4%)
||10. Pakistan (3%)
United States (2002 USDA) -
627,660 MT or 1.1 billion pounds. Value = $168 million. Yields range from 9000 lbs per acre in Arizona to 25,000
lbs/acre in Florida. Leading states: FL, CA, AZ (in order). The USA average price paid to growers is about
Lemons & Limes
World - (2002 FAO) -
11,227,173 MT or 24.7 billion pounds. Lemons and limes, as we know them
in the USA, are not distinguished by the FAO. Thus, the following data
are totals of lemon- and lime-like fruits. In Mediterranean climates
(like Spain, Italy, and California), production of lemons dominates; in
tropical and subtropical regions (like Mexico, Brazil, and Florida)
lime production dominates.
Lemons and limes are produced commercially in 94
countries worldwide, on about 1.9 million acres. Yields average 13,500 lbs/acre.
|Top 10 Countries
(% of world production)
|1. Mexico (15%)
|6. USA (7%)
|2. India (12%)
||7. Brazil (5%)
|3. Argentina (11%)
||8. Italy (5%)
|4. Iran (9%)
||9. Turkey (4%)
|5. Spain (8%)
||10. China (3%)
United States (2002 USDA):
1,095,160 MT or 2 billion pounds. Value = $341 million. California 86%,
Arizona 14%. Yields are about 16,000 lbs/acre in Arizona and
32,000 lbs/acre in California. Prices are 12-15 ¢/lb.
MT or 14 million pounds. Value = $1.7 million. Florida produced 100% of
the limes in the USA, but hurricane and disease damage has all but eliminated the Florida industry. Acreage estimates showed
1000 acres in 2002, and less than 400 in 2003.
All citrus are small, spreading, evergreen trees or
tall shrubs. Grapefruit trees are the largest, and limes
the smallest statured trees of the group. Trees may reach 20-30' in
height in nature, but most cultivated trees are <15'. Stems are
often armed with long thorns, particularly limes, and in all types when
young. Leaves are unifoliate (sometimes termed compound unifoliate to
indicate the loss of lateral leaflets over time), relatively thick,
ovate with acute to obtuse tips, having entire or crenulate margins,
and stout, winged petioles of various width depending on species
(grapefruit = wide, tangerine = narrow).
Fragrant, white flowers are solitary or in short
cymes, borne axillary on current flush of growth ("leafy
bloom"), and also without leaves from the previous flush
("bouquet bloom"). Flowers are perfect, with 5
petals and sepals; petals linear, sometimes curved lengthwise, waxy,
and thick; sepals fused at base to form a small cup. Ovary is compound with
10-14 locules in most commercial cultivars; position superior, and
subtended by raised nectary disc.
Most cultivars are self-pollinated. Some are
parthenocarpic (e.g., 'Tahiti' lime, and some Navel oranges
and tangelos). Cross pollination is necessary only for some tangerines and tangerine
Citrus fruits are so important that they have
received a special name - a hesperidium. A hesperidium is basically a
leathery rinded berry. The endocarp is the edible portion, divided into
10-14 segments separated by thin septa, each containing up to 8 seeds,
but usually only one. Each segment is composed of juice vesicles
("pulp"), with long stalks attached to the outer wall, containing
Citrus seed is unusual compared to most fruit crops
because it forms nucellar embryos (maternal clones) in addition to the
zygotic embryo produced through fertilization. Exceptions include some
tangerines and the pummelo, in which only a zygotic embryo forms.
The condition is termed nucellar embryony or polyembryony,
and it allows clonal propagation of citrus by seed, which is rare in
horticultural crops. This condition is exploited by nurserymen, but
presents obvious difficulties in citrus breeding. Multiple embryos per
seed ensures that germination rates often exceed 100%, and production
of uniform seedlings in high percentages simplifies clonal rootstock
production greatly. In other fruit crops, clonal rootstock production
requires some form of layering and an extra year in the nursery,
raising costs of tree production. For breeders, variation in seedling
progeny is low or non-existent since most seedlings arise from nucellar
embryos, and are thus clones of the maternal parent.
Soils and Climate
Wide variety of soil types
and conditions - almost pure sand in central Florida,
to organic muck near the Everglades, to loamy, heavy, high pH soils in
the San Joaquin valley of California, tolerant of high
or low pH and salinity. Citrus
species generally do not tolerate soil flooding for more than a few
days without injury.
Most citrus perform best in subtropical climates,
where there is a slight change of season but little or no chance of
freezing weather. Cold hardiness is the major limiting factor for
citrus production in subtropical areas. Flowers and fruit are killed at
about 28°F. Leaves and stems are killed by a few minutes at
20-28 F, depending on stage of acclimation, species, and age of
tissue. Flowering is induced following emergence from
quiescence, and sometimes by relief from drought.
There is perhaps no better illustration of the
influence of climate on fruit quality than in citrus. Internal and
external quality differs greatly between humid subtropical and
Mediterranean climates. Temperature and humidity are the main
environmental factors controlling quality. The following changes are
• Peels become thicker and have
more pebbly or rough texture in Mediterranean climates than in
• Peel color is best in
Mediterranean climates due to cool winters enhancing chlorophyll
destruction and fewer pests that blemish the peel.
• Juice content is higher in
subtropical than Mediterranean climates.
• Acid content is higher and sugar
content generally lower in Mediterranean than subtropical climates, due
to warmer temperatures during ripening. Acids break down faster with
warm nights, and warmer day temperatures allow greater photosynthesis.
Hence, the sugar:acid ratio is higher in Florida, and fruit is said to
be richer in flavor.
• Within arid climates, rate of
maturation is faster in hot, desert areas of California and Arizona
than in cool, coastal areas.
• On-tree storage is generally
better in Mediterranean than subtropical climates. ‘Valencia' oranges
maintain color and quality well into the summer if left on trees in
California, but will regreen if the same is done in Florida.
Although citrus seedlings will produce fruit
identical to the parent tree due to nucellar embryony, trees are
generally budded onto various rootstocks to avoid the long juvenile
period for seedlings. Budding can be performed during most of the year,
when pencil-sized, round budsticks are available, and bark slips on
rootstocks. Bud unions on citrus are generally higher than many other
tree fruits (8-12" above soil line) to avoid any contact of the scion
to the ground.
|Yield / tree
|Tolerance to Freeze damage to tree
Planting Design - rectangular
arrangements which eventually become tall hedgerows
typically 20 x 25 for grapefruit and vigorous trees, 15 x 20 for
oranges and tangerines, and 12-15 x 18-20 for limes and smaller
densities are now about 100-110 trees/acre for grapefruit, and 130-140
for sweet orange.
Training and Pruning - very little training is
needed. Young trees may be
headed at 30 inches to induce branching, and stripped of trunk
sprouts and suckers for the first 2 years. They may be defruited for a
year or two to induce vegetative growth. At maturity, trees are
mechanically hedged and topped to form hedges about 12 ft tall and
wide. Almost no hand pruning is done.
Mature citrus orchards in Yuma, Arizona seen from
the air look like parallel hedgerows (left). A grapefruit orchard in
the Indian River district of Florida has been hedged and topped
mechanically to control size.
HARVEST, POSTHARVEST HANDLING
All citrus are non-climacteric fruit, meaning that
they ripen gradually over weeks or months and are slow to abscise from
the tree. External color changes during
ripening, but is a function of climate more than ripeness, and a poor
indicator of maturity. The best indices of maturity for citrus are
internal: oBrix (sugar), acid content, and the oBrix/acid
Citrus is hand harvested, whether processed or
marketed fresh. Mechanical harvesters have been used for
processed fruit in Florida and are increasing in popularity due to high
labor costs and lack of labor availability.
For fresh fruit, standard packing line operations
are used (in order): dumping, culling, washing, brushing, waxing,
drying, grading (human), sizing, and boxing. For
processed fruit, growers are paid for "lbs-solids" or sugar content,
based on juice analysis. Harvested fruits are culled for rot, and
remaining fruit is washed prior to juicing. Juice is extracted by
inserting a cylindrical strainer in the center of the fruit and
compressing the fruit hydraulically. Extracted juice contains some pulp
and oils, which are separated from the juice by centrifugation and
screening. Juice is pooled into lots of various colors
and sugar levels; some mixing is done to produce uniform product. Sales
of frozen concentrate have been outpaced by single-strength juice
products in recent years, due to the superior flavor of the latter.
Citrus may be stored for periods of up to 1-2 months
at low temperatures (32-40°F). Chilling injury is common in
grapefruit, lemons, and limes when stored below 50°F, but rare in
oranges and tangerines. A unique aspect of citrus is the ability to store
fruit on the tree. Fruit may reach minimum maturity standards in early
winter, but since they are nonclimacteric, they ripen slowly and will
not soften or abscise for periods up to several months.
Americans derive about 26% of total vitamin C from
citrus fruits, the highest proportion from any single food group. All
other non-citrus fruits contribute another 16%, for a total of 42% from
fruit consumption. Citrus contributes only 0.9% of total daily calories
and 1.7% of daily carbohydrate intake, despite recent efforts to
characterize citrus fruits as "high carb" foods. Per capita consumption of citrus is higher than any
other fruit crop when juice and fresh consumption are combined. In
2004, U.S. citizens consumed 78.8 lbs of sweet oranges (86% as juice),
7.9 lbs of of
grapefruit (48% juice), 6.7 lbs of lemons (54% juice), 2.6 lbs of limes
(28% juice), and 3.9 lbs of tangerines (28% juice). Consumption
has been constant for most citrus fruits, except lime which has
increased and grapefruit , which has decreased.
Dietary value, per 100 gram edible portion:
* Percent of recommended daily allowance set by FDA, assuming a 154 lb
male adult, 2700 calories per day.
|Crude Fiber (%)
of US RDA*