There are four common types of Australian stinging trees. Two are large rainforest trees growing up to 30 to 35 m. The other two are really little more than bushes growing up to 3 or 4m tall but often seen as a shrub 0.1 to 1m tall. The sting inflicted by the smaller species are by far the most painful. The poison from the smaller species is the most virulent and because of their size people are more likely to blunder into them. All four are closely related and belong to the same family as the common stinging nettles.
(Urticaceae). In Australia the common native nettle is Urtica inscisa.
The four variations of the Australian stinging trees are:
Giant Stinging Tree Dendrocnide (used to be called Laportea) excelsa up to 35 m
Shiny leaf Stinging Tree Dendrocnide photinophylla up to 20 m
Atherton Tableland Stinger Dendrocnide cordata up to 4 m
Gympie Stinger Dendrocnide moroidies up to 4 meters
All of these stinging trees have thousands of hollow, hypodermic-needle-like fine silica hairs of various lengths on the leaves, stalks, and small branchlets. These hairs vary from 0.1 to 2 mm long. These hairs can be seen with the naked eye but one should never touch them with unprotected skin. Contained in these hairs is a virulent irritant poison that can cause painful wheals and waves of stabbing pain that can recur for weeks or months after being stung. The effects of a sting are described in more detail later. All four species have a similar stinging mechanism but D. moroides (the Gympie Gympie) is generally considered to have the worst sting. It has been reported that some coastal aborigines used the leaves to cure rheumatism, by stinging the affected parts. This stimulation is similar to urtication (use of nettles) practiced by sufferers in Europe.
Surprisingly, just like nettles, stinging trees make a good palatable emergency vegetable once cooked. It's just the harvesting that poses the problem.
Once you have seen a stinging tree – you will have no trouble in recognizing the common 3, although D photinophylla is harder to recognize.
The distinctive form of the stinging tree – from Lake Barrine on the Atherton tableland.
Note the serrated margins of the leaves.
Giant Stinging Tree Dendrocnide excelsa
This is a very large, soft wooded, rainforest tree found in the eastern rainforests from the Victorian border to Gympie, Queensland, around 30 m tall and 2m thick at the the base with a flanged butt. The leaves are large and heart shaped with serated edges, however unlike the D. moroides, the D. excelsa's leaves join the stalk at the notch between the overlapping lobes. (as shown below-pix. 1) The leaves on older mature trees can often have little or no hairs while younger trees' leaves have more. The leaves are often eaten by insects. It is not uncommon to see whole trees with skeletonised leaves for a canopy. (The stinging hairs offer the leaf no protection from the insects - they just get munched too). Flying foxes roost in giant stinging trees - seemingly oblivious to the stings.
See the picture below to appreciate just how big this tree is. In the Dorrigo national park, some entire forest galleries are almost pure stands of D excelsa.
Giant Stinging Tree Dendrocnide excelsa with Alocasia brisbanensis (cunjevoi) in Dorrigo National Park. (http://en.wikipedia.org/wiki/Giant_stinging_tree C Goodwin)
Shiny Leaf Stinging Tree Dendrocnide photinophylla
Other names are Mulberry Leaved Stinging Tree or Fibrewood tree. This is also a large, softwood, rainforest tree and grows up to 20m tall. The leaves have stinging hairs but differ from D. excelsa in that their leaves are shaped like spear heads, similar to mulberry leaves. (see diagram 3) The leaves are glossy on the upper surface , long and narrow shaped (6-12cm long) with wavy or sometimes toothed margins. The leaves on mature adult trees often have no stinging hairs at all. The sting from this tree is similar to D. excelsa. D photinophylla can be found in the rainforests from Bateman's Bay NSW to the coast north of Atherton Tablelands and Cooktown.
Because it doesn't look like the normal stinging tree - it can be hard to recognise.
(From the Australian National Herbarium)
Atherton Tableland Stinger Dendrocnide cordata
Common names for this plant are similar to D. moroides, (Gympie or just Stinger), as this plant is often confused with D. moroides. Grows up to 4m tall. This species is found on the Atherton Tablelands, in New Guinea and Torres Strait islands. It is a shrub similar in habit to Dendrocnide moroides with heart shape leaves but with a broad notch at the base which is inserted the leaf stalk. The leaf margins are irregularly, shallowly, and rather coarsely lobed (not toothed like D. moroides). Local experience on the Atherton Tablelands indicates that it is probably just as bad an irritant as D. moroides.
Gympie Stinger Dendrocnide moroides
Common names are Gympie Gympie, Gympie stinger, Stinging Tree or bush, or just Stinger. It's a simple stemmed and sparingly branched shrub up to about 4m tall. The leaves can be very large oval to heart shape up to 30 cm long and 20 cm broad. Sawtooth edges to the leaf are characteristic, with the blade tapering to a short point at the tip. The leaf stalk is attached to the underside of the leaf blade at some distance inside the leaf margin. The leaf is not notched at the base. The leaf has stinging hairs on both sides of the leaves including stalks and branchlets and these can be seen with the naked eye.
Gympie Stinger Dendrocnide moroides – note the ‘felty’ aspect to the leaves (due to the mass of stinging hairs) and the serrated edges to the leaves. The venation is also quite distinctive.
They're most plentiful from about Gympie in southern Qld to Cape York Peninsula and is the most common stinger in the rainforest of the Atherton Tablelands. It is less plentiful south of Gympie but has been recorded as far south as Lismore in Northern NSW. D. moroides is frequently seen along the edges of roadways and tracks through the rainforest and is a common regrowth plant in recently cleared or disturbed rainforest. Because of this liking for tracks and clearings in rainforests there is a good chance of unwary visitors to the rainforests walking into them and being severely stung. These small regrowth plants, anything from 100cm up, are considered to be the most virulent. Examples of D. moroides can easily be viewed along the walkway into Crystal Cascades reserve near Cairns Qld. as the forest rangers have painted red marks near the plants so visitors can avoid them.
As juvenile plants are just as virulent as adults, most people who get stung, get stung on the ankles and lower legs - and because they are small, these plants are not immediately visible - (and they get their well earned name of "ankle-biters" ).
Fruit colour appears to be variable - with white, pink and dark red fruit on the same species. They look a bit like mulberries - and many people have been stung trying to get them. They are quite edible - once you massage them to break the stinging hairs - but they are watery and have no particular flavour. The seeds are spread by birds.
All four types of stinging trees have a similar stinging mechanism. The severity of the sting depends on the surface area of skin making contact with the leaf, the number of hairs on that leaf and the nature of the poison contained in the hairs. D. moroides has the most virulent poison with D. cordata a close if not equal second. The venom is contained within tubular silica hairs which function as self-injecting hypodermic syringes after the tip breaks off on contact with the skin. On a large D. moroides leaf 30 cm by 20 cm there can be as many as 15,000 hairs on both sides of a single leaf.
Note the little rounded tips on the hairs, which get knocked off on contact with the skin- and leave a beveled hypodermic needle-like end which easily punctures the skin. These spines are simply elaborate hairs – found on most plants.
The composition of the venom is not understood but what is known is that it contains polypeptides which most likely stimulate the release of or mimic the actions of acetylcholine (Ach), Histamines, Hydroxtryptamine (5HT) and Neuropeptides.
The exact nature of the toxins probably varies with different species. The stinging hairs of most nettle species contain formic acid, serotonin and hisstamine; however recent studies of Urtica thunbergiana (China) implicate oxalic acid and tartaric acid, at least in that species.
A polypeptide called moroidin has been isolated from D. moroides, (ref) and it is able to generate pain when minute doses are injected sub-dermally in human subjects – but it is still not as effective as the natural sting, indicating that a ‘cocktail of compounds are required.
•Acetylcholine (Ach) has a parasympathetic stimulant effect causing vasodilation of blood vessels in the skin and sweating.
•Histamine dilates the capillaries and increases capillary permeability leading to edema, erythema, and weals.
•Hydroxtryptamine (5HT). Serotonin. is a neurotransmitter involved in pain production and vasoconstriction.
•Neuropeptides, short chain proteins, probably causes the long term pain, hyperalgesia and sensitivity to temperature. Bradykinis, SRA, Leukotrienes and others.
The surface of the silica hairs appear to be coated with a protein (which may be the polypeptide moroidin), which if the tubular hairs remain in the skin, causes long term hyperalgesia (an increased perception of pain and a lowered pain threshhold). This causes the untreated sting area to become very sensitive, especially in response to temperature changes, for many months after contact. These proteins (rather than the contents of the hairs) also appear to be largely responsible for the virulence of the pain.
However - this protein-based coating is very easily destroyed (hydrolysed) by moderately strong acids such as hydrochloric acid - which has allowed us to develop a totally effective treatment to stings of any severity.
Anyway – watch this spot – this will be another student project at the Cape Tribulation Tropical Research Station!
•Effect of the Sting
Taken from Everist “Poisonous Plants of Australia”,
"If the leaves or the twigs make contact with the skin the hollow silica-tipped hairs penetrate and there is at first a slight itch, followed in a few seconds by a severe prickling effect which quickly becomes intense pain of a complex nature. The pain is described as composed of a background of tingling on which is superimposed an intermittant stabbing pain with sharp radiations passing in all directions. After a time, which varies in length, the stabs of sharper pain decrease in intensity and frequency but the diffuse background pain increases. The sharp tingling sensation is increased by touching rubbing or cold. Referred pain in the thorax, chin, forehead, and in the opposite limb may also be experienced within 5 minutes of being stung. Pain also occurs frequently in the armpit or groin and this may persist for several days longer than the referred pain. The duller background pain may persist for several days and even after it finally disappears the affected portion may become extremely sensitive during cold weather or if rubbed or exposed to cold water. This effect may recur for 2 months or more after the original sting. Simultaneously with the production of pain the injured area quickly becomes covered with small red spots which join together and form a red swollen area surrounded by a flare zone. This effect appears within 5-10 minutes and persists for 8 hours or more. There is piloerection on the affected part generally intermittent and sometimes persisting for up to 30 hours. Sniffing and coughing have been reported in some cases."
•Why are they so nasty?
That is a bit of a mystery. From an evolutionary perspective - these plants derive from the common nettle (Urtica - which means itch giver) - which had already developed stinging hairs to deter grazing vertebrate herbivores - as the leaves of all members of the family are highly edible and nutricious. Nettles spread all over the world - including Australia and New Zealand (which has its own mean nettle, Urtica ferox, the ongaonga or tree nettle). In Australia - possibly because of the grazing pressure of the big marsupials that existed before humans arrived, bigger guns were required, and selection pressure forced the nettles to become bigger and more toxic. This didn't require the development of anything new - just the elaboration of the chemistry of the pre-existing nettle stinging hairs. Of course - this toxicity had no effect on the activities of insects, which regard the hairs as just something more to eat - as the neurochemicals involved would be destroyed by any digestive system (which is why stinging tree leaves are often reduced to leaf skeletons). Now that there are no really large veterbrate herbivores around (tree kangaroos and wallabies are reported to munch happily on D cordata!) - the plant evolution can go two ways - increasing virulence or reducing virulence - either approach probably has no real effect on the survival of the species. Here at Cape Tribulation we are seeing examples of reduced virulence - the appearance of perfectly normal looking D moroides - which don't sting! Not that we'd recommend checking!
Treatments - Then and now.
Various Older Treatments that have been tried....
Cunjevoi Northern NSW Aborigines are reported to use the plant cunjevoi (Alocasia) as an antidote. These plants are often found growing near the offending stinging tree (see the picture of the Giant stinging tree). (The rationale is a belief that the antidote grows near the offending plant) - The technique was to rub the sap of the leaf, stem, or rhizome (underground root) on the affected parts immediately. This treatment is one of the most often mentioned when talking about stinging trees but it has been proven that in Far North Queensland it has no effect and if anything worsens the pain.
(The reality seems to be that the aborigines just 'wore' the pain.)
Dettol Blake (1970) in Poisonous Plants of Australia reported that rubbing the affected parts in undiluted Dettol reduces the pain. Other individuals have found this treatment ineffective.
Hot Water Cairns District Ambulance Officers have found that immersing the affected part in hot water relieves the pain but only for as long as the part is immersed. Not too hot as there is a danger of scalding.
Chris Shaw's Remedy Chris Shaw was a local Cairns pharmacist who reportedly used to make up a 0.9% Hydrochloric acid solution to irrigate the affected part. Anecdotal evidence suggest that relief was obtained using this remedy but no recent proof has been found to confirm this.
(Comment - 'close - but no seegar ' - the acid was too dilute to be effective!)
Paw Paw Ointment This is a local Cape Tribulation treatment. No proof that it works is available but it may well provide some relief as it contains a protein digester (Protease)
Xylocaine or Lignocaine Cream This short term local anesthetic treatment lasts only as long as the cream is effective. It should probably be used only after depilatory wax treatment. If creams of any kind are used before wax treatment the wax will not grip the hairs as efficiently, reducin the effectiveness of the treatment.
Other Folklore Remedies Include spirits of ammonia, blue bags, nitrogen compounds, urine, rubbing with fine sand, and rubbing with the fleshy part of the Cassowary Plum. None of these remedies have been tried so no comment can be made about their effectiveness
Depilatory Wax Treatment
The long term recurring nature of a D. moroides and cordata sting is due to the silica hypodermic hairs remaining below the skin level until the body can physically repel them out of the skin, this can take months. The use of depilatory wax although designed to remove human hairs is an effective method of removing stinging tree hairs. This treatment was developed in the 1990’s by Dr.Hugh Spencer of the Australian Tropical Research Foundation (AUSTROP) and has since been used by many people including tour operators in tropical rainforest areas. Stings from all types of stinging trees are treated in the same manner. This treatment recommends using "Waxeeze" a sugar-based depilatory (like very sticky toffee) which is readily available from most pharmacies, but in effect any strip depiliatory will do.
Comment: - Not bad - but not totally reliable - especially if the victim scratched or shaved the stung area - making it hard for the wax to grip the stinging hairs and pull them out. However - it has become the final component of the new first aid measure described here.
This has been developed at the Cape Tribulation Tropical Research Station over the past 10 years where investigation of the toxin has been the subject of several student studies. (we get called upon to treat about 2 stings a year from locals and tourists - it's been a long time since Cyclone Rhona!- as stinging trees really get going after a cyclone).
With this treatment – the pain and after-sensitivity is completely gone in about 12 hours after treatment (as opposed to waiting for 3-6 months!).
We call it the acid and hairstrip approach.
1. What you need.
Make up a solution of 10-15% hydrochloric acid in water. Hydrochloric acid (commonly sold for cleaning cement and brickwork)- produces very unpleasant choking fumes when concentrated - but is fine when diluted about 1 in 8 with water, which is what we use. Hydrochloric acid is the acid produced by our stomachs (at about the same concentration that we use for the treatment! ) - in fact, for a condition known as achlorohydria - people actually drink acid of this dilution - not pleasant - but it is essentially non-toxic - being a natural product of our bodies.
The diluted acid will not harm the skin or most materials (but keep it away from metal utensils - use glass or plastic) - however it stings quite intensely if it gets in cuts, so if you have cut or scratched hands- use a pair of latex throwaway gloves to apply it.
2. Applying the acid.
We use strips of tissue or toilet paper, laid over the affected area, and the acid poured over that to saturate the paper (and patted gently into close contact with the skin) . IT WILL STING LIKE ANYTHING - for about 5- 10 minutes - and then the sting will subside - sorry about that - but it is simply reacting with the damaged tissues as it moves down the stinging hairs - and neutralising (hydrolysing) the protein. For very young children - I suspect you will have to use fairly copious amounts of xylocaine gel first - wash it off once it has taken effect - and then apply the acid. It's a case of a short sharp shock to eliminate the long term misery and pain of the sting.
We usually add a little more of the acid after about 10 minutes - and leave the tissues in place for at least 1/2 hour.
This is also why it must be emphasized that the victim should NEVER scratch the stung area - it exposes more damaged skin - and the pain from the acid treatment, although brief, will be worse.
For a light sting - this is usually enough. For a bad sting, it will be necessary to use depilatory strips to remove the stinging hairs (and the victim's as well!).
3 Application of wax.
The aim of applying the wax is to remove as many of the stinging hairs as possible. With this end in mind the wax must be applied as gently as possible so as not to break off the brittle silica hairs making them almost impossible to remove. This is why Waxeeze is preferred over the conventional strips. In warm weather the wax can be spread with a knife like honey. In cold climates the Waxeeze may need to be warmed so it flow more easily.
(Using Waxeze - a sugar based product)
We recommend this material over say 'Nair' depilatory strips, because it can be kept in a first aid kit without degrading over time - especially in the tropics. It is a bit more 'fuss and muss' than depilatory strips but is gentler in application.
Step 1 Spread the wax directly on a linen strip, handkerchief, shirt, or whatever is available. Spreading the wax onto the cloth first minimizes the chances of breaking the hairs as would happen if you spread the wax directly onto the skin.
Step 2 Gently pat the linen on the affected area. The application of the wax can cause considerable pain in the short term but once the treatment is finished the pain quickly goes away.
Step 3 Leave the linen strip in place for five minutes to allow the body heat to soften the wax more and allow it to flow around the hairs providing better grip.
Step 4 After the five minutes the cloth is ripped off in on fast movement. If possible rip the cloth off against the direction of the stinging hairs. This will remove the stinging hairs as well as the victim's own body hairs.
Repeat this procedure if the stinging hairs are not all gone. If all the new wax is used up linen strips can be reused.
Immediately after the wax treatment Xylocaine or Lignocaine cream or similar can be applied to the affected area for pain relief.
From reports, all pain can be expected to be gone by the next day although some itching has been reported. It is important that the victim does not scratch or rub. Antihistamines don't seem to reduce the severity of the pain but they might reduce the inflammatory responses.
Don't use the lotions sometimes included in the Waxeeze package as it contains chloroform which will make this type of pain worse!!!
While this treatment works as a treatment, if there are symptoms such as asthma or other autonomic signs consult a doctor
First Aid Kit:
A first aid kit can be made up consisting of a small pot of waxeeze, linen cloth strips, a candle and lighter to warm the wax if required; all contained in a small container. A 25 ml plastic bottle of concentrated hydrochloric acid would give 200 ml of acid solution. Make sure it is well sealed! (put the bottle inside a small non-shatterable plastic jar - include 1 teaspoon of bicarbonate of soda in the jar)- as leaking HCl can ruin everything in its immediate vicinity - especially metals). Don't forget a couple of disposable latex gloves - and you'll need some of your toilet paper too! This kit is small enough to be carried by bushwalkers or workers in rainforest areas where the chance of being stung is greatest.
Picture of kit...
Fu H.Y et al, Identification of oxalic acid and tartaric acid as major persistant pain producing toxins in the stinging hairs of the nettle, Urtica thunbergiana. 2006 Annal of Botany, 98 57-65.
Lam V K T Analysis of the toxin from the stinging tree Dendrocnide moroides. 2006 Student report (unpublished) Cape Tribulation Tropical Research Station.
Leung C, et al Structural studies on the peptide Moroidin from Laportea moroides. 1986
Tetrahedron 42 12 pp.3333-3348.
Oelrichs P.B and Robertson P.A. 1970, Purification of pain producing substances from Dendrocnide (Laportea) moroides, Toxicon, 8, 89-90.