Kangaroo Apples (Part 24)

Solanum aviculare [ripe fruit - Mt. Annan] 20230102_150100 sml.jpg

"[They are] not eaten by kangaroos, and taste nothing like apples." (Low, 1991: 68). Rainforest kangaroo apples, Mt. Annan Botanical Gardens, Camden. © JPM, 2022

Names

Hailing from the ever-popular Solanum (S.) genus, there are four notable species of these eastern forest and mountain plants: the rainforest kangaroo apple (Solanum aviculare); the common kangaroo apple or poroporo in Maori (S. laciniatum); the endangered mountain kangaroo apple (S. linearifolium); and the green kangaroo apple or gunyang (S. vescum). The common name kangaroo apple apparently comes from the fact that the leaves of older, 2-lobed plants resembles the hind-leg paw-print of those marsupials.

Kangaroo apples have as their closest familiar relative the South American tamarillo (S. betaceam), which will not be otherwise covered further here.

Habitat and Range

These intrepid plants, akin to their smaller, black-berried cousins (S. nigrum and S. americanum), are often first colonisers of disturbed ground in forests, orchards and agricultural fields alike. They spring up eagerly after bushfires, logging or other land clearing activities. In the wild, they can be found in wet rainforests and wet sclerophyll bushland. They prefer rich, moist, fertile soil abundant in nitrogen and phosphorous, but can survive in some of the drier and nitrogen deficient woodlands of the east coast. They are common at altitude for much of the Great Dividing Range the from southern Queensland into New South Wales, Victoria and Tasmania. I have regularly found rainforest kangaroo apple (S. aviculare) on fire trail margins and 4WD tracks where they are often hacked down or poisoned as annoying weeds by ignorant councils and members of the public.

Figure 1. Distribution of the rainforest kangaroo apple (S. aviculare). Atlas of Living Australia.
Solanum aviculare distribution map.png


Figure 2. Distribution of the common kangaroo apple (S. laciniatum). Atlas of Living Australia.
Solanum laciniatum distribution map.png


Figure 3. Distribution of the mountain kangaroo apple (S. linearifolium). Atlas of Living Australia.
Solanum linearifolium distribution map.png


Figure 4. Distribution of the green kangaroo apple (S. vescum). Atlas of Living Australia.
Solanum vescum distribution map.png


Identification

Key Identifying Features
  • Usually a small tree or shrub 1.5 to 3 metres in height
  • Leaves are long, 20-40cm, and typically have 2, 4 or 6 lobes, especially while plants are young (S. linearifolium lacks lobes completely)
  • Leaves on older plants become lance-tipped and have 0 lobes, but both leaf features may be present on the same plant
  • Flower buds sprout on trusses 10-20 cm long
  • Flowers are light blue or white to deep violet with prominent yellow stamens in the centre
  • Flowers are vibration pollinated (wind or bees) and set into green, egg-shaped unripe fruit
  • Fruit ripen in midsummer (usually late January), becoming dark orange-red (S. aviculare) or yellow/streaky yellow (S. laciniatum, S. linearifolium, S. vescum).
  • Fruit contain dozens of tiny pale seeds
Kangaroo apples are fairly distinctive woodland shrubs. Most of these plants, particularly the rainforest kangaroo apple (S. aviculare & S. laciniatum), have distinctive lobed foliage when young, which is a good sign that fruiting adult plants may also be in the vicinity. Young plants and branches also have dark brownish-black stems. Mature plants are much taller, often exceeding 2.5 metres, with knobbly, paler trunks. The endangered mountain kangaroo apple (S. linearifolium) has very thin leaves, entirely lacking lobes. The green kangaroo apple (S. vescum) has crinkly-textured foliage, but can be lobed or straight.

Figure 5. A young rainforest kangaroo apple (S. aviculare), displaying dark stem and distinctive 6-lobed leaves. Blue Gum Walking Track, Hornsby. © JPM, 2022.
Solanum aviculare [young plant] 20221211_142407 sml.jpg


Figure 6. Close-up of a 6-lobed S. aviculare leaf punctuated with slug damage and hand for size comparison. Blue Gum Walking Track, Hornsby. © JPM, 2022.
Solanum aviculare [leaf] 20221120_154730 sml.jpg


Figure 7. An older and taller rainforest kangaroo apple (S. aviculare) displaying 2-lobed foliage. This plant stood at about 3 metres. Blue Gum Walking Track, Hornsby. © JPM, 2022.
Solanum aviculare [foliage] 20221211_141115 sml.jpg


Figure 8. Close-up of another specimen (S. aviculare) in the same region with no lobes. Blue Gum Walking Track, Hornsby. © JPM, 2022.

Solanum aviculare [foliage] 20221211_140948 sml.jpg


Figure 9. Kangaroo apple foliage (S. laciniatum). Some of the leaves are 2-lobed; many lack lobes. Atlas of Living Australia. © Anonymous, 2022.
Solanum laciniatum [foliage variation - ATLAS - Anon., 2022].jpeg


Figure 10. The mountain kangaroo apple (S. linearifolium, foreground) has long, thin leaves. Atlas of Living Australia. © Anonymous, 2022.
Solanum linearifolium [plant - ATLAS - Anon., 2022].jpeg


Figure 11. Green kangaroo apple (S. vescum) displaying crinkled, 4-lobed foliage. Atlas of Living Australia. © M. Campbell, 2020.
Solanum vescum [plant - ATLAS - M. Campbell, 2020].jpeg


Figure 12. Closeup of the dark stem of a young rainforest kangaroo apple (S. aviculare) plant. Blue Gum Walking Track, Hornsby. © JPM, 2022.
Solanum aviculare [stem] 20221211_140727 sml.jpg


Figure 13. Closeup of the gnarly trunk of an older rainforest kangaroo apple (S. aviculare) plant. Blue Gum Walking Track, Hornsby. © JPM, 2022.
Solanum aviculare [trunk] 20221211_141022 sml.jpg


In mid-late December, plants begin flowering on long, emerging trusses similar to eggplant/aubergine (S. melongena), with whom they are related. Flowers are much like aubergine, being star-shaped with five distinguishable petals and 5 yellow stamens in the core, tightly encasing a single white pistil. Flowers are not always of help to distinguish the different species, but S. aviculare and S. vescum will tend to have light to moderate purple blossoms; S. laciniatum and S. linearifolium will have deep violet (rarely, white) flowers.

Figure 14. Flowers and unopened buds on a rainforest kangaroo apple (S. aviculare). Blue Gum Walking Track, Hornsby. © JPM, 2022.
Solanum aviculare [flower & buds] 20221120_154758 sml.jpg


Figure 15. Closeup of rainforest kangaroo apple (S. aviculare) flower. Blue Gum Walking Track, Hornsby. © JPM, 2022.
Solanum aviculare [flower] 20221211_141048 sml.jpg


Figure 16. The deep violet flowers of the common kangaroo apple (S. laciniatum) stands in stark contrast with their yellow anthers. Atlas of Living Australia. © C. Gordes, 2014.
Solanum laciniatum [flowers - ATLAS - C. Gordes, 2014].jpeg


Figure 17. Flowers and ripe fruit on a mountain kangaroo apple (S. linearifolium). Atlas of Living Australia. © M. Fagg, n.d.
Solanum linearifolium [fruit & flowers - ATLAS - M. Fagg, n.d.].jpeg


Figure 18. Example of a white-flowered mountain kangaroo apple (S. linearifolium). Atlas of Living Australia. © Loz, 2021.
Solanum linearifolium [plant & white flowers - ATLAS - Loz, 2021].jpeg


Figure 19. Purple flowers contrast the crinkly foliage of the green kangaroo apple (S. vescum). Atlas of Living Australia. © H. Krajewsky, 2020.
Solanum vescum [foliage & flowers - ATLAS - H. Krajewsky, 2020].jpeg


The flowers usually self-pollinate with help by native bees and set quickly into unripe, green, egg-shaped fruits. The fruits of S. aviculare ripen to a deep orange; S. laciniatum ripens to varying shades of yellow; S. linearifolium and S. vescum may also have reddish or greenish streaks on the fruit skin, respectively. All species signify their fruits' ripeness by splitting or bursting. It can thus be difficult to find fruit at optimum ripeness.

Figure 20. Unripe, green, egg-shaped fruit of the rainforest kangaroo apple (S. aviculare). Fruits are at their most poisonous in this state. Blue Gum Walking Track, Hornsby. © JPM, 2022.
Solanum aviculare [fruits] 20221120_155112 sml.jpg


Figure 21. Ripening fruits of rainforest kangaroo apple (S. aviculare). Note the contrasting dark stems. Mt. Annan Botanical Garden, Camden. © JPM, 2023.
Solanum aviculare [ripe fruit - Mt. Annan] 20230102_150144 sml.jpg


Figure 22. Fully ripe, bursting fruit of rainforest kangaroo apple (S. aviculare). Mt. Annan Botanical Garden, Camden. © JPM, 2023.
Solanum aviculare [bursting fruit - Mt. Annan] 20230102_150233 sml.jpg


Figure 23. Ripe and bursting yellow fruit of the common kangaroo apple (S. laciniatum). Atlas of Living Australia. © Demonrowe, 2022.
Solanum laciniatum [fruit - ATLAS - Demonrowe, 2022].jpeg


Figure 24. The ripe, streaky reddish-yellow fruit of the rarer mountain kangaroo apple (S. linearifolium). Atlas of Living Australia. © M. Fagg, n.d.
Solanum linearifolium [fruit - ATLAS - M. Fagg, n.d.].jpeg


Figure 25. Ripening, streaky green-yellow fruit of the green kangaroo apple (S. vescum). Atlas of Living Australia. © N. Haigh, 2021.
Solanum vescum [fruit - ATLAS - N. Haigh, 2021].jpeg


Culinary Uses

Kangaroo apples were once a staple fruit of many First Nations tribes living in on the east coast, particularly in southern parts of New South Wales, Victoria and Tasmania (Maiden, 1889: 57-58). The Gunai tribe of Victoria's Gippsland region were known to deliberately burn forested areas where green kangaroo apple (C. vescum) was prolific in order to provoke its regrowth and lengthen fruiting season (Gott, 2008: 219).

Flowering and fruiting typically occurs in midsummer, from early December into March, but only bursting fruit are fully ripe. Samples of S. aviculare I have tasted resembled bittersweet mandarin in flavour, indicative of their alkaloid content (see Caution below). Low (1991: 68) recommends moderate consumption of the orange-fruited S. aviculare due to its high content of those toxins. Maiden (1889: 58) seemed to have far more enthusiasm for unhindered consumption of bursting fruit, noting that unripe fruit has a tendency to taste acrid; the warning is not repeated by Low for the other species (S. laciniatum, S. linearifolium & S. vescum; see Low, 1991: 133), indicating that these may be eaten with relative impunity. Fruit may be eaten raw, or cooked by boiling or roasting. They might make an interesting native salsa if tomatoes were replaced with these strange fruits, although the hundreds of gritty seeds inside detracts.

I should note that the mountain kangaroo apple (S. linearifolium) is classified as endangered in some states, especially Victoria. This species should not be damaged if found in the wild and, if possible, any harvested seeds discarded in the region of harvest to promote regrowth of this increasingly rare plant.

Figure 26. What to expect inside a rainforest kangaroo apple (S. aviculare) - lots of gritty seeds! The flavour was strangely addictive. Mt. Annan Botanical Gardens, Camden. © JPM, 2023.
Solanum aviculare [ripe & cut fruit - Mt. Annan] 20230102_150435 sml.jpg


Medicinal Uses

Unripe, green fruit and leaves of S. linearifolium has been tested to contain significant quantities of the alkaloids solasodine and solamargine (Lim, 2013 VI: 337). Generally this species has been little researched for its biomedicinal properties, but they should be similar to other Solanaceae-family plants, like blackberry nightshade, which also have varying quantities of these phytochemicals. Some studies cited by Lim (2013: 337) discuss the anticancer properties of solasodine glycoside in the cream Zycure (Curaderm), which showed effectiveness in alleviating skin cancer. However, Lim may have misidentified his intended species (S. linearifolium) with Apple of Sodom (S. linnaeanum; see Williams, 2013 IV: 472-478) which has a similar name and anticancer properties. A primitive version might be as simple as crushing green fruit or leaves and applying it as a topical poultice to skin cancers, although the commercial creams have solasodine glycoalkaloid concentrations at a mere 0.005% (Williams, 2013 IV: 476), thus some measure of dilution ought to be followed.

Rainforest and common kangaroo apples (S. aviculare and S. laciniatum) have been commercially farmed in several eastern European countries since the early 1970s, notably Russia and Hungary, as a commercial source of these same glycoalkaloids (solasodine, solamargine, solanidine, etc) for the production of steroidal contraceptive drugs and cortisone (Williams, 2013 IV: 452-454). These plants have considerable quantities of these alkaloids: S. aviculare contains 0.3-3.1% dry weight solasodine in the leaf and 1.7-3.5% dry weight in the unripe fruit (0.8-1.7% in ripe fruit); S. laciniatum has 1% dry weight solasodine in the leaves, 0.3-3.5% in unripe fruit and 0.1-0.7% in ripe fruit (Williams, 2013 IV: 456). The common kangaroo apple similarly found use in traditional Maori medicine as a poultice for many kinds of skin disorders - itches, scabies, ulcers, boils and sores; little is known about Australian First Nation medicinal uses for the plants (Williams 2013 IV: 457).

Other Uses

A quirky and underappreciated application of these native shrubs is as graft stock for creating the famous eggplant tree or tomato tree (Eliades, 2010). Branches or stems from eggplant or tomato plants can be grafted whole onto these robust Aussie Solanum species for a hardy, fruiting eggplant or tomato shrub that will last for a few years. Pruning of rootstock shoots is all the maintenance required to keep a grafted eggplant or tomato on a S. aviculare rootstock happy and healthy.

Look-alikes

Due to the general size of the plants (2+ metres) and their distinctive foliage and fruits, there are few look-alikes. It is possible that non-native tamarillos (S. betaceam) could be confused for native kangaroo apples where grown commercially in Australia, but tamarillo leaves are much broader and lack lobes; its flowers are almost always white and angular, like blackberry nightshade flowers. Other native Solanaceae-family plants, namely the bush tomatoes, have very similar fluffy purple flowers but are typically thorny shrubs with velvety foliage and they prefer to grow in arid areas, not in wet forests like the kangaroo apples.

Caution: Toxic Alkaloids!

As covered above under the Medicinal Uses section above, all of these plants contain appreciable levels of various glycoalkaloids, ranging from 0.1 to 3.5% dry weight in the ripe fruit, which are toxic when consumed in high doses. The human palate can taste these poisons at 140 mg/kg as a bitter sensation and toxic doses are listed as 200-1,000 mg/kg; symptoms of poisoning include nausea, vomiting, sweats and narcotic (painkilling) sensations such as numbness (Ojiwo, 2013: 11). Common kangaroo apple (S. laciniatum) and green kangaroo apple (S. vescum) have appreciably less toxins (0.1-0.7% dry weight solasodine in ripe fruit) and can be eaten with more hearty gusto.

References and Further Reading

Atlas of Living Australia, "Solanum aviculare." [LINK]
Atlas of Living Australia, "Solanum laciniatum." [LINK]
Atlas of Living Australia, "Solanum linearifolium." [LINK]
Atlas of Living Australia, "Solanum vescum." [LINK]
Eliades, Angelo (2010), "How to Graft Eggplant onto Devil Plant." Deep Green Permaculture [LINK]
Gott, Beth (2008), “Indigenous use of plants in south-eastern Australia.” Telopea 12(2): 215-226 [Pdf download LINK]
Lim (2013), "Solanum linearifolium." Edible Plants Vol. VI, pp. 336-338.
Low (1989), Bush Tucker, pp. 41.
Low (1991), Wild Food, pp. 68 & 133.
Maiden (1889), Useful Native Plants, pp. 57-58.
Ojiewo et al. (2013), "Exploiting the Genetic Diversity of Vegetable African Nightshades," Bioremediation, Biodiversity and Bioavailabilty 7(1): 6-13 [Pdf download LINK]
Williams (2013), Medicinal Plants, Vol. IV, pp. 450-490.
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