Hesperidiums Of The Rutaceae

Assorted Citrus Fruits: A. and B. Eureka and Meyer's Lemons (Citrus limon); C. Tangerine or Mandarin Orange (C. reticulata = C. nobilis); D. and E. Navel and Valencia Oranges (C. sinensis); F. Tangelo (C. x tangelo). The tangelo is a hybrid produced by crossing a Tangerine (C. reticulata) with a Grapefruit (C. x paradisi). The grapefruit (C. x paradisi) is another hybrid between the Shaddock or Pomelo (C. maxima) and the Sweet Orange (C. sinensis).

Blood oranges, another variety of Citrus sinensis characterized by red pigmentation (anthocyanins) in the flesh. These oranges have been described as having a rich orange flavor with overtones of raspberries or strawberries.

A. Grapefruit (Citrus x paradisi); B. Mandarin Orange or Tangerine (C. reticulata); C: Tangelo (Citrus x tangelo). The Tangelo is a hybrid produced by crossing a Grapefruit (C. x paradisi) with a Tangerine (C. reticulata). The grapefruit (C. x paradisi) is another hybrid between the Shaddock or Pomelo (C. maxima) and the Sweet Orange (C. sinensis).

Shaddock or pomelo (Citrus maxima). These large citrus fruits are about 6 inches (15 cm) in diameter. This species is crossed with a sweet orange (C. sinensis) to produce the grapefruit (Citrus x paradisi).

A large shaddock or pomelo (Citrus maxima). These over-sized citrus fruits are about 6 inches (15 cm) in diameter. This species is crossed with a sweet orange (C. sinensis) to produce the grapefruit (Citrus x paradisi).

A large shaddock or pomelo (Citrus maxima). This over-sized citrus fruit is almost 8 inches (20 cm) in diameter. It is crossed with a sweet orange (C. sinensis) to produce the grapefruit (Citrus x paradisi).

Hesperidium Anatomy: Berry with a leathery rind.

The lemon (Citrus lemon) is a hesperidium, a berry with a leathery rind. The exocarp (peel) contains volatile oil glands (essential oils) in pits. The fleshy interior (endocarp) is composed of separate sections (carpels) filled with fluid-filled sacs (vesicles) that are actually specialized hair cells.

Close-up view of the peel (exocarp) of a lemon (Citrus lemon) showing numerous pits containing volatile oil glands. Essential oils (terpenes and phenolic compounds) in the pits are responsible for the aroma given off when the peels are bruised or ground up. The fragrant perfume called bergamot comes from the fruit rinds of Citrus bergamia (C. aurantium ssp. bergamia). Essential oils in the pits of skins are extracted by maceration and modern hydraulic presses. The bitter chemical found in the mesocarp and parchment-like layers (partitions) surrounding the sections (carpels) of citrus fruits is limonin.

Magnified longitudinal view of the endocarp of an orange (Citrus sinensis) showing several sections (carpels) filled with numerous fluid-filled "juice sacs." The two lower sections each contain a seed which is surrounded by the fleshy sacs. The sacs (vesicles) are actually swollen (plump), specialized hairs. According to K. Esau (Anatomy of Seed Plants, 1960), the juice sacs originate as multicellular hairs in which the interior of the enlarged distal part breaks down and fills with liquid. The juice sacs constitute the fleshy, edible pulp of an orange and are the source of the sweet juice. A bitter compound called limonin occurs in the mesocarp (rind) and membranous layers (partitions) surrounding the seed-bearing sections of grapefruits and other members of the citrus family (Rutaceae).

A large shaddock or pomelo (Citrus maxima) showing fluid-filled "juice sacs" (juice vessicles). The sacs (vesicles) are actually swollen (plump), specialized hairs. This large citrus fruit is almost 8 inches (20 cm) in diameter. It is crossed with a sweet orange (C. sinensis) to produce the grapefruit (Citrus x paradisi).

Left: Lime (Citrus aurantiifolia), a spiny tree native to tropical Asia. There are several varieties including the small, round "bartenders lime" ('Mexican') and the larger California cultivar 'Bearss.' The 'Mexican' cultivar is also grown in the Florida keys and is the source of delicious "key lime pie." Right: Kumquat (Fortunella margarita = Citrus japonica), a citrus relative native to tropical Asia. Bigeneric hybrids between limes and kumquats are called "limequats" and are placed in the hybrid genus (x Citrofortunella).

Sweet lime (Citrus limettioides), not to be confused with the sweet lemon (C. limetta).

The calamondin (x Citrofortunella microcarpa) is a hybrid fruit resembling a miniature orange. It is the result of a cross between the tangerine or Mandarin orange (Citrus reticulata) and the kumquat (Fortunella margarita = Citrus japonica). Although the flesh is quite sour, the peel is sweet. The bigeneric hybrid Citrofortunella also includes the limequat, a cross between the lime (C. aurantiifolia) and the kumquat (F. margarita = Citrus japonica).

According to Citrus Pages by Jorma Koskinen (2009) the genus Fortunella is taxonomically invalid.
Therefore, all of the varieties and hybrids of kumquats should be listed under Citrus japonicaThunb.

Buddha's Hand or Fingered Citron (Citrus medica var. sarcodactylis)

Citrus medica var. sarcodactylis is an unusually shaped citron variety whose fruit is segmented into finger-like sections. The following is from Wikipedia (accessed 9 Jan. 2020): "The different cultivars and variations of this citron variety form a gradient from "open-hand" types with outward-splayed segments to "closed-hand" types, in which the fingers are kept together. There are also half-fingered fruits, in which the basal side is united and the apical side fingered. The origin of this kind of citron is commonly traced back to the Far East, probably northeastern India or China, where most domesticated citrus fruits originate. Buddha's hand fruit is very fragrant and is used predominantly in China, Malaysia and Japan for perfuming rooms and personal items such as clothing. Unlike other citrus fruits, most varieties of the Buddha's hand fruit contain no pulp or juice. Though esteemed chiefly for its "exquisite form and aroma", the Buddha’s hand fruit can also be eaten (often as a zest or flavouring) in desserts, savory dishes and alcoholic beverages (such as vodka) or candied as a sweet. The sliced, dried peel of immature fruits is also prescribed as a tonic in traditional medicine." The fruit in above image came from the Palomar Campus Botanical Garden.

Longitudinal section of Buddha's hand fruit.

Botanical Gazette

Magnified image of juice vesicle (juice sac) taken through compound microscope with back-lighting (40x). The fluid-filled vesicle is a swollen multicellular structure with a hairlike stalk. The following is from Katherine Esau (1962) Anatomy of Seed Plants: "The juice sacs are comparable to multicellular hairs but originate subepidermally, with the epidermis forming a single layer. The distal part of each hair is enlarged, and the interior broken down and filled with juice."

More Images Of Juice Vesicles In Finger Lime

Two San Diego Native Shrubs In The Citrus Family (Rutaceae)

Bush Rue (Cneoridium dumosum), a native member of the citrus family in the chaparral of San Diego County. The small globose fruits and white blossoms superficially resemble miniature oranges. This shrub is also called "spice bush" because of the fragrant foliage and stems when the are crushed.

Turpentine Broom (Thamnosma montana), a native shrub in the citrus family occasionally encountered when hiking in the Anza-Borrego Desert area. The pitted, gland-dotted, aromatic fruits are typical of the Rutaceae.

Other Members Of The Citrus Family

White sapote (Casimiroa edulis), a native tree in the highlands of Mexico and Central America. Although this tree belongs to the citrus family (Rutaceae), the fleshy, very sweet fruits are not true hesperidiums as in oranges and grapefruits. They are drupelike and contain several large seeds. The delicious fruits are eaten fresh, and used for fruit salads, sauces, desserts, milkshakes and preserves. Mamey sapote (Pouteria sapota) is a widespread tropical American tree. It belongs to the sapodilla family (Sapotaceae) along with the sapodilla or naseberry tree (Manilkara zapota). It is listed incorrectly in some references as Calocarpum mammosum. In the Rio Napo region of Ecuador, the shiny black seeds are used in necklaces. Another mamey fruit called the mammee apple (Mammea americana) comes from a native Caribbean tree in the garcinia family (Guttiferae).

See Fruit Of Chicle Tree Or Naseberry

Curry leaf tree (Murraya koenigii), native to India and Ceylon. The aromatic leaves are a common ingredient in curries and chutneys. Crushed dried leaves are an ingredient in curry powder.

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