A newly described species from Goodenough Island, Papua New Guinea
Port Moresby in Papua New Guinea lies approximately 150 Kms from mainland Australia and is home to Citrus wintersii (formerly Microcitrus papuana), first described in 1976. It grows in the Brown River region inland from Port Moresby.

The home of Citrus warburgiana (formerly Microcitrus warburgiana) is further south-east along the coast of Papua New Guinea.

Still further from the tip of Australia - some 800 Kms - is Goodenough Island. In the 1950's, the noted botanist and plant collector L.J.Brass reported finding citrus species on the island.

Slender tree 3 m tall; fruits (unripe) yellowish green.  Collected by L.J. Brass on the 4th Archbold Expedition to New Guinea (March-November 1953).
Mabberley's 1988 article on Australian Citreae is available here
In September 2000, Malcolm Smith of  Bundaberg Research Station (Queensland's Department of Agriculture, Fisheries & Forestry) visited Goodenough Island in Papua New Guinea to re-locate the citrus trees first reported by Brass. Details were published in Austrobaileya and the article is available here. Working together with Paul Forster, he showed that they were a new and undescribed citrus species differing from Citrus warburgiana in several respects.
The illustrations above are a re-arrangement of the drawings of Citrus wakonai published in Austrobaileya 8(2): 133-138 (2010).     PDF version available for download here.
Citrus tristeza virus (CTV) is an economically important disease of citrus that is found worldwide. Researchers at Bundaberg are working on producing improved rootstocks for commercial citrus, with the particular aim to remove any susceptability to CTV, before introducing other useful characteristics. Citrus wakonai is helpful in hybridisation studies because, unlike most citrus, it flowers and fruits in its first year from seed. Research has focussed on crossing C. wakonai with C. glauca (the Australian Desert Lime), and further crossing with Poncirus trifoliata; as well as C. wakonai with the African citrus relative Citropsis gabunensis.
CTV Factsheet from Queensland

Small tree up to 6m tall. Bark corky, cream; foliage glossy, dark green above, paler below; flowers white; fruit obovoid, surface rough, irregular, yellow-green when mature; flesh dull, pale yellow. Very common at locality of collection and from where the seed for this cultivation were taken.
From BingMaps an aerial view of the roadless Wakonai village.
I finally found the exact location of Wakonai via the German version of Wikipedia, see details here, but I have since found the best maps of the area are still the wartime Australian military maps, although of-course most of the military installations have by now disappeared:
The Austrobaileya article says  the local name for the fruits of C. wakonai is kamokuku. The local language for this very remote area is called Iduna. Interestingly, I found an Iduna-English dictionary in which the word for a lemon is also listed as kamokuku.
Fruit images from
First Fruiting Intergeneric Hybrids between Citrus and Citropsis J. AMER. SOC. HORT. SCI. 138(1):57-63. 2013. PDF click here.
Fruit of Citrus wakonai
This information poster was produced for The International Citrus Congress, Valencia, Spain 2012. It covers some of the Queensland rootstock research using Citrus wakonai

Full size poster here
This new species was named Citrus wakonai - 'Wakonai' being the village nearest the citrus trees. However, I had great difficulty  locating any map showing a village with this name. Even the entry in Brisbane Herbarium fails to reveal the exact co-ordinates. It says:
With thanks to Malcolm Smith, Bundaberg Research Station, Queensland, Australia who provided information and images for this page.
Fancy a trip to Wakonai? Read this account first!
Flowering twig of Citrus wakonai growing at Bundaberg Research Station
Click photo above for bigger version

The native vegetation found on Goodenough Island varies from open savannah-like grassland to dense forest.  The black & white photo above is a view of Wakonai village taken during the 1954 Archbold  Expedition. The war-time Vivigani airstrip is just visible near the top of the picture.

The lower colour photo, taken in 2000, shows a plant of Citrus wakonai in its native habitat.

page created 8th January 2014
Do you have any more information on Citrus wakonai?
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In part as a result of reading this page, intrepid Frenchman Sylvain, set off in August 2014 to find Citrus wakonai. Read all about his adventures in:
The Quest for Wakonai!
These photos of Citrus wakonai are all from Sylvain's expedition to Wakonai village, Goodenough Island, Papua New Guinea

There is an herbarium sheet of one of the original collections in the National Herbarium of the Netherlands. Presumably specimens were sent to various institutions. There doesn't appear to be any original identification, apart possibly by a hand written 'Microcitrus', but it is catalogued as Citrus garrawayae, as determined by David Mabberley in 1998.
I am surprised by the 'garrawayae' identification. Geographically 'warburgiana' would have been more likely. The leaf shape, as well as the fruit shape, is noticeably different from both species. Clearly, at the time, Mabberley did not consider that this might be a distinct unnamed species.
All these pictures are from one herbarium sheet.
You can view the complete sheet here.
Finally, here are photos I took on a visit to Bundaberg Research Facility, Queensland in October 2016. The plants grown from seeds collected in PNG are thriving and have been crossed with many other citrus species and near relatives. This is the species 'type specimen' - although some botanical authorities say you can't have a living type specimen! The fruits are about 8cms long.

The  two northernmost citrus species endemic to Australia are Citrus gracilis and Citrus garrawayi. Named and first botanically described by Mabberley in 1988, Citrus gracilis grows in the Darwin region of Australia's Northern Territory. Citrus garrawayae (formerly Microcitrus garrawayae) grows in the far north of Queensland.

I have recently received a copy of another Brass specimen held in the Harvard University Herbarium. This is the one referred to in the first sheet as 'Flowering material under 24918.'
In 1981 this sheet was annoted as 'Microcitrus australasica' by another noted botanist, B.C. Stone. Once again, the possibility of a new citrus species does not seem to have been considered.
The identification as Microcitrus australasica (Fingerlime) is even more surprising than Mabberley's garrawayae. The Fingerlime is a sub-tropical rainforest species from the Queensland and New South Wales border area.
To add to the confusion, the entries for the two Brass sheets in the Lae Herbarium in Papua New Guinea, give identifications of Citrus warburgiana and Microcitrus australis, the Round Lime.

So now we have four different citrus species for one plant!
These pictures are from one herbarium sheet. You can
view the complete sheet here.

See also Australia2016
Early mis-identification 1:
Early mis-identification 2:
Mis-identifications 3 & 4: