Citrus australasica, popularly known as the finger lime, is a citrus fruit part of the wider Rutaceae family. Finger lime grows in tropical and subtropical rainforests of Australia located on the east coast of the continent, between south east areas of the state of Queensland and north east New South Wales.
Depending on the location, the finger lime can be considered a large shrub or a small tree and reaches a maximum height of 6 m. Aromatic oil glands are located on the leaves and branches are protected by thorns of about 2.5 cm. It blooms between late autumn and the next summer, while the lemons mature during the months of May and June. Flowers can be pale pink or white, while the fruits display a variety of colors. They can have green, yellow, purple, brown or even black skin, while the flesh is green, pink or yellow. The lemon finger fruit is famous for its special aroma and taste similar to caviar, which gives it a high commercial value. Citrus australasica 'Alstonville', Citrus australasica 'Blunobia Pink Crystal', Citrus australasica 'Judy's Everbearing', Citrus australasica 'Durhams Emerald' and Citrus australasica 'Pink Ice' are the five cultivars that are currently accepted.
Marmalades prepared from finger lime fruits harvested in the wild have become popular for the first time in the 1990s. This prompted the first commercial plantations and 10 years later finger limes were an established ingredient in Australian restaurants and fresh fruits were already available for export.
The high value and increasing demand for finger limes has recently increased the number of commercial plantations in Australia. For the same reason, there is more and more genetic selection and grafting. However, the popularity of the species has been quite sudden, so selected wild stock remains the main source for propagation.
Since ancient times, lemons have been known as the kings of citrus. The finger lime has a similar taste to lemons, limes and other related species. Finger lime is commonly used to prepare a refreshing drink, by squeezing the juice of a fresh fruit in a glass of cold water. It is a major source of vitamin A, which is a very strong antioxidant. It plays many roles inside the human body and protects the cells from mutations that can cause cancer and other very serious conditions.
Vitamin A is especially needed by our eyes and an increased intake is helpful for people with poor vision. It can make eyesight more effective and correct a number of issues, such as night blindness. Finger limes are also a major source of potassium, an essential mineral that reduces hypertension. High blood pressure can be very dangerous and people who suffer from it should include finger limes in their daily diet. The potassium provided by the finger lime fruits can prevent other diseases as well. High amounts of this essential mineral can prevent the formation of stones in the kidney, which are very painful and difficult to remove. Scientists now understand the mechanism behind kidney stones and know how to decrease the risk with a proper diet.
As calcium builds up in the kidneys, it creates the structures popularly named kidney stones. Potassium can prevent their formation because it balances the levels of calcium, as part of a natural mechanism. At the same time, increased levels of potassium can reduce the risk of prostate, colon or breast cancer. Another benefit observed by scientists in people who consume finger limes is a proper blood count. It is also a major source of vitamin D, which is required for bone and teeth durability. Due to the high antioxidant content, finger lime fruits also provide a boost to our immune system and can fight infections like flu or cold.
The finger lime fruit has been obscure for a long time but is now considered to be a bush food delicacy. It is widely praised as a cooking ingredient or garnish and its taste has been compared to caviar. The finger lime releases its flavour as you chew it and is an excellent addition to many recipes. It is quite similar in taste and acidity to a normal lime and its peel can be used as a spice after it is dried. Most often, the finger lime fruit is pickled or prepared as marmalade.
Unlike other citrus fruits, finger limes can be eaten raw. However, their most popular uses are as a garnish to other types or food or as an ingredient in many dishes. It pairs best with light recipes based on chicken meat or seafood. The delicate aroma and sourness of the finger lime is a great addition to deserts based on cream or melons. It is also a very popular addition to oyster shooters, since the added flavour and crunch goes very well with this dish. It complements basically any fish and seafood recipe, especially seared scallop or grilled salmon.
A very popular and easy to prepare gourmet dish is sliced avocado or melon with a topping of finger lime juice and a bit of sea salt. The result is very refreshing and a great snack choice during the hot summers of Australia. The finger lime fruit has also become an ingredient in cocktails and other drinks and it is used by bartenders as a floating garnish and an exquisite addition. The flavour resembles other citrus varieties but it has a special touch. Finger lime caviar is a gourmet side dish for many foods such as cheesecake, sushi, grilled shrimps or ceviche.
The species requires tropical or subtropical climates and tolerates many types of rainforest soils. It can also be cultivated in temperate regions, where it needs irrigation and soils with a high content of loam. It enjoys acidic soils rich in nutrients, with a high percentage of organic waste. Even if it is a tropical tree, it can survive minor frost. However, if the climate is temperate, it should be planted in sheltered locations facing north. It needs irrigation during the summer, mulching in the spring and some pruning every autumn after the fruits are harvested. As long as the soil is fertile, no fertilizer is needed.
Seeds can be used for propagation but cuttings and even grafting on other varieties of citrus are popular as well. Finger lime grows very slowly from seed and up to 15 years are needed until it reaches maturity. Fresh seeds are very viable but the rate of success decreases if they get old. Cuttings of semi-hardwood are used for propagation and grow as slowly as the ones from seeds. In order to speed up the rate of growth, root hormones can be used. Containers with a capacity of 100 litres are the best choice for both seedlings and cuttings. Grafting the finger lime on other citrus species has many advantages. It develops a lot faster and the resulting plant is more tolerant to climate and soil variations. The Troyer citrange and Citrus trifoliata are the most common species used for grafting.
When cultivated south of Sydney, the rate of flowering and fruit production decreases dramatically due to improper climate. The tree is also vulnerable to grasshoppers, aphids, caterpillars and other insects. It is also sensitive to strong winds and long-term sun exposure and can be affected by Melanose oleocellosis, a fungal disease that attacks its oil glands.