Mar 062010
 

Photo © Bulleen Art & Garden

Botanical names: It is generally accepted that there are 3 (possibly up to 5) original citrus species and all the rest are hybrids of these (excluding the wild species still being discovered – at least 6 in Australia). Citrus have been hybridised frequently over a long time and over wide geographic boundaries, consequently, there is a great deal of confusion around correct botanical names of commonly known citrus. As genetic testing progresses, some of the more disputed classifications will be resolved, but in the meantime we are choosing to use the classifications of Prof David Mabberley, an eminent botanist and taxonomist.

POMELO
Citrus maxima (Sometimes incorrectly referred to as Citrus grandis)
Described by Johannes Burman in 1755 as Aurantium maximum and then in 1842 as Citrus grandis by Justus Hasskarl. In 1915 the confusion was cleared up by Elmer Merril who renamed it Citrus maxima (acknowledging the earlier description by Burman).
Believed to originate in the Malay archipelago. One of the original citrus species, and by hybridising with the mandarin is involved in the parentage of several of our current citrus:
Citrus × aurantium (pomelo x mandarin) which includes the following pomelo hybrids
1. Sour Orange (e.g. Seville orange). The sour orange has inherited more features from the pomelo than from the mandarin
2. Sweet Orange (e.g. Navel Orange, Valencia Orange). The sweet orange has inherited more features from the mandarin than the pomelo. This group also includes all the crosses of orange, mandarin and grapefruit such as tangors, ortaniques, tangelos and clementines.
3. Grapefruit: These are the pomelo backcrossed with the orange.

CITRON
Citrus medica
Referred to as Citron. Used as a Jewish symbol and called Etrog in Hebrew.
Citrus medica var. sarcodactylis, or the fingered citron is referred to as Buddha’s hand in China, Japan and Korea. Used there mainly in perfumery, but also as a temple gift.
Citrus medica is one of the original species and with hybridisation is involved in many well-known current citrus (hybrid parents in brackets).
Citrus x limon, (citron × sour orange) gives us our lemons and similar hybrids such as the sweet limes (sometimes called Palestinian/Indian/common sweet Lime)
Citrus × jambhiri, (citron × mandarin) produces the rough lemon (commonly used as a good rootstock) and similar hybrids like Rangpur lime and Mandarin lime
Citrus × aurantiifolia, (citron × lemon × Ichang papeda) gives us the well-loved lime (Lime/Key Lime/West Indian Lime/Mexican Lime).
Citrus × bergamia, (citron × sour/bitter orange) gives the wonderfully scented Bergamot orange.

MANDARINS
Citrus reticulata
Mandarins are still to be thoroughly genetically tested and there are two main groups of thought on their classification. One keeps all the species together under Citrus reticulata and the other gives tangerines and satsumas their own species. For the purposes of this fact sheet we will keep them all grouped together and wait for genetic testing to definitively sort it out later.
One of the original species, varieties of this species includes the mandarins, tangerines, and satsumas.
• Mandarins
• Tangerines – closely related to, or a type of mandarin. Referred to as Citrus tangerine by those who believe it belongs in a separate species. Similar to an orange, but smaller, sweeter and stronger. Very thin peel and easily peeled like a mandarin.
• Satsumas – closely related to, or a type of mandarin. Referred to as Citrus unshiu by those who believe it belongs in a separate species. Seedless with a sweet delicate flesh. Loose, thin slightly leathery easily removed peel. Similar in size and shape to mandarins.
Extensively hybridised with citron hybrids, pomelos and pomelo hybrids to form a wide range of oranges, grapefruits and specialty citrus. It is the mandarin that adds the sweetness to these hybrids.

CUMQUAT OR KUMQUAT
Citrus japonica – formerly known as a separate genus Fortunella japonica
Within this species are several separate groups:
• Marumi/Morganni/Meiwa
These are the round cumquats, with sweet skin but sour flesh. Used in marmalades and brandied cumquats, as well as other forms of preserves.
• Nagami
These are the oval cumquats with very sweet soft skin, allowing the fruit to be eaten whole; the sweet skin contrasting with the sour flesh giving a pleasant sweet/tart flavour. Smaller growing than their round cousins, they are ideal in pots. Like all cumquats they are prolific fruiting.
Also produces a variegated form, sometimes called centennial cumquat.
Cumquats have been used in hybridisation to create new edible citrus, two of which are readily available in Australia:
• Calamondin (x citrofortunella microcarpa): A hybrid of a mandarin orange and a cumquat
• Limequat: A hybrid between a Key Lime and a cumquat.

AUSTRALIAN LIMES
There are debatably 7 species of Australian limes. The Finger limes are the most readily known and have been recently used in hybridising to produce various new hybrids. Native limes currently available in the nursery industry include:
FINGER LIMES
(Citrus australasica). Sometimes referred to as Microcitrus australasica
These come in an array of colours from almost clear, to yellow, green, pink, and reds. Desirable for culinary use due to their citrus tang and their caviar like vesicles.
ROUND LIME (DOOJA)
(Citrus australis)
A round lime similar to the Key lime. A distinct and pleasant flavour.
DESERT LIME
(Citrus glauca) formerly Eremocitrus glauca
Heat, drought, salt and cold tolerant characteristics have made this lime useful for breeding and hybridising. The fruit is small with a distinct lime flavour.

CITRUS HYBRIDS

CLEMENTINE
(Citrus x clementina). Arguably a hybrid between a mandarin and a sweet orange, but some consider it to belong to the Citrus reticulata species. Very similar to satsumas and tangerines.

TANGELO
A hybrid of a tangerine (Citrus reticulata) and either a pomelo or a grapefruit.
• Honeybell Tangelo is a hybrid cross between a Thompson Tangerine and a pomelo
• Minneola Tangelo is a cross between a Duncan Grapefruit and a Dancy Tangerine
• Seminole Tangelo is a cross between a Bowen grapefruit and Dancy Tangerine

YUZU
(Citrus x junos).
Bred from crossing Citrus x ichangensis and Citrus reticulata.¬ The C. ichangensis (also called Ichang papeda and regarded by some as a subgenus of the citrus genus) parent gives the Yuzu its cold tolerance. The Yuzu has a tart grapefruit like flavour with mandarin overtones. Very aromatic peel.

TAHITIAN LIME (also called Persian Lime)
Citrus x latifolia
A highly regarded hybrid lime, regarded as a new species and as such has an ‘x’ before the species name. The correct botanical name is Citrus × latifolia. Generally believed to be a cross between the key lime (Citrus × aurantiifolia) and a lemon (Citrus × limon).
A heavy bearing tree producing juicy seedless fruit with a fine rind and little pith. They are conventionally eaten green, before they turn yellow at full maturity and lose flavour.

LIME OR KEY LIME (also called West Indian or Mexican Lime)
Citrus x aurantiifolia
Smaller, seedier and more acidic than the Tahitian Lime, with a thinner rind and a more aromatic flavour. Used in the classic Key Lime Pie (from the Florida Keys – hence sometimes know as Key Lime).
The tree is thorny and shrubby to 5m. Not frost tolerant, needs a warm protected position in Melbourne.

INDONESIAN LIME
Unknown botanical name
This lime is only a recent introduction to Australia and currently grown by Engalls in NSW. It produces a small flat fruit, turning from green to yellow / orange when fully ripe, mainly in winter. They are incredibly juicy and the tree is only small, but very dense and bushy. Fruit has conventionally been used in cooking, especially as a marinade for meat.

RANGPUR LIME
Citrus x jambhiri
A hybrid between a mandarin and a citron hybrid

ORANGES
Citrus x aurantium
The oranges are hybrids of the pomelo and the mandarin, deriving their sweetness from their mandarin parent. Both sweet and bitter oranges are included in this grouping. The sweet oranges include many subgroupings such as Navel Oranges and Blood (or pigmented) Oranges. The sour oranges include Chinotto (Citrus x aurantium var. myrtifolia) and Seville.
Oranges are also involved in backcrossing and further hybridisation to give more edible citrus such as the grapefruits (Pomelo crossed with orange), bergamot oranges (Pomelo cross bitter orange) and lemons (Citron x bitter orange)

LEMONS
Citrus x limon
A hybrid between a bitter orange and Citron
There are many different cultivars, the two most common in Australia being the Lisbon and Eureka.
The other commonly grown lemon is the Meyer lemon (Citrus x meyeri) and it is believed to be a hybrid of a true lemon and either a mandarin or orange.

GRAPEFRUIT
Citrus x aurantium (Often referred to as Citrus x paradisi)
A hybrid derived from backcrossing a sweet orange with a pomelo. Can be highly acidic to sweet, and yellow, pink or red.
Used in further hybridisation to create tangelo varieties.