Finger Lime
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''Citrus australasica'', the finger lime or caviar lime, is a thorny
understorey In forestry and ecology, understory (American English), or understorey (Commonwealth English), also known as underbrush or undergrowth, includes plant life growing beneath the forest canopy without penetrating it to any great extent, but above ...
shrub or small tree of lowland subtropical rainforest in the coastal border region of
Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...
and
New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...
, Australia. It has edible fruits which are grown as a commercial crop.


Description

''Citrus australasica'' is a shrub or small tree to about tall with sharp spines up to long in the . The leaves are light green in colour,
obovate The following terms are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (that is, the leaf blade or 'lamina' is undivided) or compound (that is, the leaf blade is divided into two or more leaflets) ...
or rhombic in shape, and arranged
alternate Alternative or alternate may refer to: Arts, entertainment and media * Alternative (''Kamen Rider''), a character in the Japanese TV series ''Kamen Rider Ryuki'' * Alternative comics, or independent comics are an alternative to mainstream superh ...
ly along the twigs. They measure up to wide and long, but may reach long, and they may be faintly (scalloped) towards the apex. Like many other plants in the genus, the leaves contain numerous oil glands and are aromatic when crushed. The flowers are either solitary or paired and are set on peduncles about long. The
sepal A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106 Etymology The term ''sepalum'' ...
s are tiny, about long, the white petals are up to long. Stamens number between 20 and 25. The fruit is a botanical
berry A berry is a small, pulpy, and often edible fruit. Typically, berries are juicy, rounded, brightly colored, sweet, sour or tart, and do not have a stone or pit although many pips or seeds may be present. Common examples of berries in the cul ...
, cylindrical and tapered at both ends, slightly curved and about long. The skin is rough with numerous oil glands, and greenish yellow to pink. They contain numerous pale seeds about long.


Taxonomy

This species was first described by Australian botanist
Ferdinand von Mueller Baron Sir Ferdinand Jacob Heinrich von Mueller, (; 30 June 1825 – 10 October 1896) was a German-Australian physician, geographer, and most notably, a botanist. He was appointed government botanist for the then colony of Victoria, Australia ...
, and was published in the first volume of his massive work '' Fragmenta phytographiæ Australiæ'' in 1858. American botanist
Walter Tennyson Swingle Walter Tennyson Swingle (January 8, 1871 – January 19, 1952) was an American agricultural Botany, botanist who contributed greatly to the classification and citrus taxonomy, taxonomy of citrus. Biography Swingle was born in South Canaan, Cana ...
, in a 1915 review of the genus ''Citrus'', placed all four Australian species in a new genus ''Microcitrus'', based on morphological features which he said gave " ..these plants a very different aspect from the commonly cultivated species of Citrus." However, in a paper published in 1998, British botanist
David Mabberley Professor David John Mabberley , (born May 1948) is a British botanist, educator and writer. Among his varied scientific interests is the taxonomy of tropical plants, especially trees of the families Labiatae, Meliaceae and Rutaceae (in parti ...
discussed the mix of morphological features present throughout the subtribe Citrineae (genera ''Clymenia'', ''Eremocitrus'', ''Fortunella'', ''Microcitrus'' and ''Poncirus'') and the ease with which species can be crossed, and subsequently restored the finger lime to ''Citrus''.


Distribution and habitat

The finger lime is native to the southeastern corner of Queensland and the northeastern corner of New South Wales, from the area around
Brisbane Brisbane ( ; ) is the List of Australian capital cities, capital and largest city of the States and territories of Australia, state of Queensland and the list of cities in Australia by population, third-most populous city in Australia, with a ...
to the Clarence River. It grows in coastal rainforest and extends into neighbouring open forest, often on soils derived from basalt. It is favoured by disturbance.


Conservation

, this species has been assessed to be of
least concern A least-concern species is a species that has been evaluated and categorized by the International Union for Conservation of Nature (IUCN) as not being a focus of wildlife conservation because the specific species is still plentiful in the wil ...
by the
International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...
(IUCN) and by the Queensland Government under its Nature Conservation Act.


Pests and diseases

The finger lime is susceptible to a range of insect pests, including
scale insect Scale insects are small insects of the Order (biology), order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient g ...
s,
katydid Insects in the family Tettigoniidae are commonly called katydids (especially in North America) or bush crickets. They have previously been known as "long-horned grasshoppers". More than 8,000 species are known. Part of the suborder Ensifera, the ...
s, larvae of various moths and butterflies, some bugs, grasshoppers and others. However, it is not a host to the Queensland fruit fly ''Bactrocera tryoni'', saving Australian growers the extra burden of treatment before export. Research conducted since the 1970s indicated that a wild selection of ''C. australasica'' was highly resistant to '' Phytophthora citrophthora'' root disease, which has resulted in a cross-breeding program with finger lime to develop disease-resistant citrus rootstock. In 2020, researchers began working with ''C. australasica'' to develop solutions for
Citrus greening disease Citrus greening disease ( abbr. HLB) is a disease of citrus caused by a vector-transmitted pathogen. The causative agents are motile bacteria, '' Liberibacter'' spp. The disease is transmitted by the Asian citrus psyllid, '' Diaphorina citri'', ...
.


Cultivation and uses


History

It is thought that for at least 60,000 years, First Peoples living along the east coast of Australia have been eating finger limes. The fruit is high in vitamin C and the skin can be used to heal cuts and wounds. Early settlers consumed the fruit and retained the trees when clearing for agriculture. Colonial botanists suggested that they should be cultivated, due to the lack of citrus alternatives.


Rising demand

The finger lime has been popularised as a gourmet
bushfood Bush tucker, also called bush food, is any food native to Australia and historically eaten by Indigenous Australians and Torres Strait Islander peoples, but it can also describe any native flora, fauna, or fungi used for culinary or medicinal ...
. The globular
juice vesicles The juice vesicles, also known as citrus kernels (in aggregate, citrus pulp), of a citrus fruit are the membranous content of the fruit's endocarp. The vesicles contain the juice of the fruit and appear shiny and saclike. Vesicles come in two sha ...
(also known as pearls) have been called "lime caviar", and can be used as a garnish or added to various recipes. The fresh vesicles have the effect of a burst of effervescent tangy flavour as they are chewed. The juice is acidic and similar to that of a lime. Marmalade and pickles are also made from finger lime. Finger lime peel can be dried and used as a spice. Commercial use of finger lime fruit started in the mid-1990s with boutique marmalades made from wild harvested fruit. By 2000 the finger lime was being sold in restaurants, and exported fresh. The finger lime is grown on a commercial basis in Australia in response to high demand for the fruit. There is an increasing range of genetic selections which are budded onto
citrus rootstock Citrus rootstock are plants used as rootstock for citrus plants. A rootstock plant must be compatible for scion grafting, and resistant to common threats, such as drought, frost, and common citrus diseases. Principal rootstocks Five types of roo ...
. With the sudden high market demand for the fruit the primary source of genetic material for propagation has been selections from wild stock. The
CSIRO The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is an Australian Government agency that is responsible for scientific research and its commercial and industrial applications. CSIRO works with leading organisations arou ...
has also developed several ''Citrus'' hybrids by crossing the finger lime with standard ''Citrus'' species, creating
cultivars A cultivar is a kind of cultivated plant that people have selected for desired traits and which retains those traits when propagated. Methods used to propagate cultivars include division, root and stem cuttings, offsets, grafting, tissue cult ...
which produce finger limes in many different colours ranging from light pink to deep blue-green. Finger lime is thought to have the widest range of colour variation within any ''
Citrus ''Citrus'' is a genus of flowering trees and shrubs in the family Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, mandarins, lemons, grapefruits, pomelos, and limes. ''Citrus'' is nativ ...
'' species.


Gallery


References


External links


View a map
of recorded sightings of this species at the
Australasian Virtual Herbarium The ''Australasian Virtual Herbarium'' (AVH) is an online resource that allows access to plant specimen data held by various Australian and New Zealand herbaria. It is part of the Atlas of Living Australia (ALA), and was formed by the amalgama ...

See images
of this species on Flickriver.com
View observations
of this species on
iNaturalist iNaturalist is an American 501(c)(3) nonprofit social network of naturalists, citizen scientists, and biologists built on the concept of mapping and sharing observations of biodiversity across the globe. iNaturalist may be accessed via its web ...
* {{Taxonbar, from1=Q50837145 Australian Aboriginal bushcraft Australian cuisine Bushfood australasica Crops originating from Australia Edible fruits Flora of New South Wales Flora of Queensland australasica Plants described in 1858 Sapindales of Australia Taxa named by Ferdinand von Mueller