Native Limes

Citrus species.

Native lime. Mt. Annan Botanical Garden. © JPM, 2022.

If it looks like citrus, smells like citrus, and tastes like citrus, is it a citrus? What if they're really small?

Names

Australia happens to be home to a number of native citrus species that have been bush food favourites for many millennia. Several decades ago these were classified under the subfamilies Eremocitrus and Microcitrus, and some older works still utilise these classifications. However, recent taxonomy has simplified the matter and all Australian native limes are now all classified as Citrus (C.). Prominent wild varieties include the desert lime, C. glauca; the finger lime, C. australasica; the wild round lime, C. australis; the Mt. White lime, C. garrawayi; and the endangered Russell River lime, C. inodora.

Dozens of hybrid cultivars have been selectively bred from native Australian limes, especially the finger limes, resulting in an immense array of subvarieties exhibiting fruit of every colour imaginable - red, yellow, pink, orange, green, brown and purple e.g. [LINK] (no affiliation). The desert lime, C. glauca, has also been experimented with to produce hardy, drought-tolerant root stock for grafting purposes for commercial citrus varieties.

Habitat and Range

In the wild, native citrus have a rather limited range. C. australasica, the finger limes, and C. australis, the wild round limes, are rainforest plants which grow almost exclusively in wet, well-draining, rich-soiled regions of South-East Queensland, from the NSW border region to Gympie. The Mount White lime may be found exclusively in that region of the Cape York peninsula, as can the rare Russell River lime, also at home in Cape York. Look for small, under-story shrubs of 1 to 2 metres in height, usually standing alone as native citrus do not cope well with competition. The rainforest varieties prefer semi-sheltered or sheltered situations but do not cope with heavy frost very well, making them unsuitable for inland regions.

Desert limes (C. glauca) are somewhat more common, frequenting the arid regions of western Queensland, the Northern Territory, and western NSW. Look for them near dry creek beds, billabongs and rock outcrops, although some may occur sitting alone in the middle of the desert. In the dry season, desert citrus will lose all their leaves and just resemble a green, spiky shrub. After rain their thick, stubby leaves will reappear, along with splays of white flowers and copious small, round fruits. Desert limes are suitable for open or dry situations with full sun and can cope with heavy desert frosts.

Due to extensive research and hybridisation with Australian native citrus, especially the C. australasica (finger lime) varieties, commercially available cultivars mean that every Australian garden may now be home to these beautiful plants.

Figure 1. Distribution of native citrus (all species) across the continent. Note that this map includes commercial citrus cultivars. Atlas of Living Australia.

Identification

Key Identifying Features

• Small understory shrub or tree, typically 1-3 metres in height

• Branches and stems have thorns 2-5 cm in length

• Leaves are small, 2-4 cm in length (except C. inodora, which has large, 5-10 cm orange-like leaves)

• White or yellow flowers emerging twice per year with a strong citrus fragrance (except C. inodora, which produces no citrus oils in flower or fruit)

• Fruits are thin and elongated (finger limes, Russell River and Mt White limes), or stubby and round (desert and native limes)

• Fruit flesh exhibits a 'caviar' effect when squeezed out

Generally, Australian citrus, especially the finger limes and desert limes, have short or stubby leaves about the size of a thumbnail, 1 to 2 cm long, and thorny stems like some European or Asian lemon species. The Russell River lime bucks the trend, having large, orange-like leaves of 5-10 cm length but retaining the thorns of the other native species. All species display white flowers similar to other citrus species, although the Russell River lime lacks the strong aroma of commercial citrus varieties.

Fruit can be round (C. australis; C. glauca) or elongated (C. australasica; C. garrawayi; C. inodora), usually green in colour, occasionally turning yellow when fruit becomes fully ripe. Some varieties, especially the commercial finger lime hybrid cultivars (C. australasica), have great varieties of colour in the fruits, as covered above.

Figure 2. Desert lime tree, C. glauca. This is a dormant specimen, waiting for rain, displaying its very long thorns. Atlas of Living Australia.

Figure 3. Desert lime, C. glauca, in full bloom after rain. Atlas of Living Australia.

Figure 4. C. australis, the native lime, also in the header image at the top of this article. Stubby green leaves, thorny stems and small round fruit. Atlas of Living Australia.

Figure 5. Mt. White lime, C. garrawayi, of the Cape York peninsula. Again, note the stubby leaves, prominent thorns and elongated fruit. Atlas of Living Australia.

Figure 6. Russell River lime, C. inodora. This species develops into long yellow fruits. Atlas of Living Australia.

Figure 7. Round lime, C. australis. From Mt. Annan Botanical Gardens, NSW. © JPM, 2022.

Figure 8. Commercial finger lime cultivar 'Byron Sunrise' exhibiting the classical 'caviar' effect. Atlas of Living Australia.

Culinary Uses

Native citrus, especially the finger limes, have had increasing culinary interest over the last few decades. Commercially available cultivars are well known for exhibiting the 'caviar' effect (figure 8 above), due to the fact that the juicy nodules inside the fruit do not readily stick to the skin or pith. Thus, they can simply be squeezed out of the fruits after cutting them across the girth. They can be added as a delightful, zinging acidic garnish to any dish that appreciates a citrus tang, such as seafood, pasta, salads and cocktails.

Fruits of the desert lime were sought out for their vitamin C by First Nations and colonists alike. All native citrus are suitable for marmalades, jams, jellies and candied peel. Zests may be used to evoke the potent citrus oil flavours, some of which are similar to lemon or lime. The variety I sampled above (figure 7) tasted almost exactly like the pub drink "lemon, lime and bitters", minus the fizz! They make excellent Korean preserve teas.

With so many finger lime cultivars now available in Australian nurseries across the continent, there is no reason for any Australian garden to lack one of these delightful Australian limes.