Microcitrus

The Microcitrus group contains seven species, five of which are native to Australia with the other two found in New Guinea. The Australian species occur in rainforests and their margins from Cape Yorke Peninsula, south to the Northern Rivers of New South Wales.

They produce small, round or finger-shaped fruit, with a pleasant but very acid juice.

Citrus australasica (previously Microcitrus australasica), commonly known as the Australian finger lime, occurs as an understorey shrub or tree in rainforests in southern Queensland and northern New South Wales. It produces finger-shaped fruit, up to 10cm long, with thin green or yellow skin and green-yellow compressed juice vesicles that tend to burst out when the skin is cut. A pink to red-fleshed form with red to purple or even black skin (known as Citrus australasica var. sanguinea) also occurs in the wild.

Australian Finger Limes

Citrus australis (previously Microcitrus australis), commonly known as the Australian round lime. A shrub or tall narrow tree occurring on the open and drier rainforest margins of southeast Queensland, from Brisbane northwards. It produces round fruit with a thick, green to lemoncoloured skin and pale green pulp, very similar to a small commercial lime in appearance.

A hybrid between Citrus australasica and Citrus australis, commonly called the ‘Sydney hybrid’, is known and was provisionally given the scientific name of Microcitrus virgata before its hybrid nature was established. It is notable for its extreme vigour, exceeding that of all other known citrus in the length of twigs produced. More than 200 metres of twigs were borne on a single branch, 3 cm in diameter, of a Sydney hybrid growing near Riverside, California, which survived for several decades on land no longer irrigated and where conventional citrus trees made little or no growth.

Citrus inodora (previously Microcitrus inodora), commonly known as the Russel River lime or Large-leaf Australian wild lime, is now rare in the wild, being native to the high-rainfall lowland rainforest between Cairns and Innisfail, much of which has now been cleared to grow sugar cane or bananas. It is a shrub or small tree and produces a lemon-shaped fruit. Fruit is not traded commercially.

Citrus garrowayi (previously Microcitrus garrowayi), commonly known as the Mount White lime, occurs in rainforest on Cape Yorke Peninsula. It produces a finger-shaped fruit, similar to Citrus australasica though shorter and thicker, with a pale lemon skin and light green pulp. The species is considered rare in the wild and fruit is not traded commercially.

Citrus maideniana (previously Microcitrus maideniana), commonly known as Maiden’s Australian wild lime, is reported to have the same distribution as Citrus inodora and is very similar to in appearance, with a sunken apex as its main distinguishing feature. It may in fact be a variation of Citrus inodora, rather than a separate species.

Eremocitrus

The Eremocitrus group contains one species, Citrus glauca (previously Eremocitrus glauca), known commonly as the Australian desert lime. A similar species, Citrus gracilis, the Humpty Doo or Kakadu Lime, has recently been described.

Citrus glauca grows wild in Queensland and New South Wales, west of a line running from Rockhampton to Dubbo, with some isolated occurrences in central South Australia. It is the only known member of the citrus family which is a xerophyte (i.e. adapted to withstand drought).

Seedlings develop a large root system before making vigorous aerial growth and under extreme drought the leaves fall and the leafless twigs carry on photosynthesis. The plant tolerates high temperatures (up to 45°C) and when dormant in late winter is able to withstand temperatures of –24°C, or lower, without injury. The roots are able to endure high salt concentrations. It has the shortest flowering to fruit maturity period (about 8 weeks) of any member of the citrus family.

It is likely that the desert lime shared a common ancestor with the more coastal Microcitrus types and has been spreading slowly westward over a long period of time, during which it has become adapted to a semiarid climate and saline soils.

Trees vary from short shrubs, only 2 to 3m high and often forming thickets, to tall upright trees up to 12m high. The fruit resembles a small, thin-skinned, yellow-green lime. It is juicy, pleasantly acid and often seedless.

Citrus gracilis has recently been described and grows wild as a straggling tree in Eucalypt woodland in the Northern Territory. It has a similar growth habit to Citrus glauca and produces round fruit up to 8cm in diameter.

 

Source Anthony Hele, Industry Development Consultant, Native Foods
 
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