The Spiny Fern of Death!

Brisbane, Australia

Hello all, just need a little help identifying a monster plant!

First post here. Quite an avid gardener, but we've moved into a new house and found what can only be described as a Spiny Fern of Death in the garden. It is VERY well established, with long, flexible branches that spread out through the lawn (quite nasty to step on) and it has also wrapped itself all around the nearby trees, some of its branches grown out to around 30ft long in its aggressive expansion.
It's evergreen, with very lush, widely distributed leaves, but at night, or during cooler weather, or even when people go near it for more than a couple of minutes, the leaves fold away, leaving the spines exposed.
The fern-like leaves are made up of much tinier leaves, but are about 18" wide at their largest, and about 10" wide at their smallest, and easily a foot to two feet long. The spines mostly stick up around a half inch, but some of the more established branches have spines up to an inch and a half long.
Its branches start out green, but turn grey after they've matured, and once they turn grey, they're almost impossible to cut. We have - quite literally - had hedge trimmers and even chainsaws break trying to cut this thing. It even bent the blade of my machete! The branches at the outer edges are about a quarter inch thick, but as you go deeper into the plant (if you dare) they get up to an inch thick easily. At its base, its a good 3 inches thick on each "tendril".
Trying to kill it off using RoundUp only made it burst into flower. It started growing these pale yellow bushy flowers all over it. Thousands of them.
The worst part about the plant is the smell it gives off. Not only does it smell like rotting paw paw, it makes you come over with a strange feeling like you need to just run away from it. It's so strong that even the dogs won't go near it and seem terrified of it. If you get pricked by the spines the feeling becomes even stronger. You break into a sweat and get very anxious very quickly. Since the branches are quite bendy and springy, when one spine sticks into you, your movement trying to get away from it makes the rest of the bush start swaying and more and more branches latch onto you, effectively trapping you until someone comes and helps you out.
This thing is so strong, so horrible to get scratched by and so hardy, that I've even had thoughts of using its branches as a form of natural barbed wire (I have quite a large property)

At first I thought it was a fern, given the formation of its leaves, but looking around, the closest thing I can find to it online is the 'Vachellia farnesiana' which grows a lot here in Australia, but its leaf formations are far too wide and thick for it to be that plant, since they usually look quite spindly.

Below you can find some photos of this monster. Any help identifying it would be very helpful!

The flowers:
The leaf formations:
The spines on a young branch:
More spines:
The base of the tree:
New branches growing as it spreads:

Thank you all very much in advance!

Beautiful, BC(Zone 8b)

At first I thought it might be Parkinsonia but the blooms are wrong. Looks like it's in the Mimosaceae family. An Acacia of some sort?

Beautiful, BC(Zone 8b)

I'm starting to think it might be: but I can't find any reference to spines. The reason I came across this plant is because of a report by Queensland Primary Industries and Fisheries as a weed potential: (PDF) . Another listing but states "unarmed"

Brisbane, Australia

Indeed. I've found the same things in my attempts to look it up. I can find things that look VERRRY similar but without the spines, and at first I thought it was part of the Acacia family as well, but the leaf formations are WAY too big for that... Unless it's some sort of mutant, which I suppose is theoretically possible.

Scott County, KY(Zone 5b)

Post pictures directly into the thread - links break (or aren't looked at) and thus are useless to the community in identifying this plant and to future users of this site.

Where do you live in Brisbane? I'll advise my niece and her husband to stay away from your environmental hazard...

Municipality of Murr, PA

Mimosa pigra is listed as an invasive here
And here:

The flowers seem pinker than yours, but these are official AUS sites. Hope this helps!

Prairieville, LA(Zone 9a)

I wonder if there is not another species/variety similar to Mimosa pigra (Black Mimosa) Everything I have read about it says pink to mauve flowers and Alex's plant is not an exact match for the Mimosa pigra we encountered at Peter Faust Dam. There is a white blooming Mimosa, Mimosa pellita (cat's claw mimosa) that is listed as a synonym for M pigra even though it has white blooms.

Brisbane, Australia

It's possible! But yes, definitely my creature has very pale yellow blossoms. Nothing even remotely pink or purple or mauve. It's also been here a VERY long time by the look of how well established it is, and how thoroughly it has wrapped itself around nearby trees, but there are no other of its kind near it, so it hasn't been spreading at all. Also, despite the aggressive flowering, there are no seed pods or fruit visible.

Other than that, it matches the description quite well, though NOTHING I have tried will even slightly harm the thing. It's quite amazing, really. Like I said, even pouring pure, undiluted roundup at its base just made it go into flower within a week!

Another main difference though is the size of the "fronds" or leaf formations. They are much bigger on my plant than what is described for the Mimosa shrubs...

Beautiful, BC(Zone 8b)

Remember, a plant can go into bloom just before it croaks. Give it a bit of time. A Thuja will take up to 2 years to die.

Brisbane, Australia

Good to know! I'll have to keep an eye on it.

Just... You know.... From a distance....

While holding a flamethrower.....

Beautiful, BC(Zone 8b)

Have you thought of pruners and a chainsaw? We do it with blackberry. Prune of bits of the branches at a time until you get to the trunk. I use the pruners to lift the plant pieces into garbage bags.

Brisbane, Australia

Like I said in the initial description, it's broken both a hedge trimmer and a chainsaw, and hedge clippers and machetes actually get their blades NOTCHED on it! :O It actually tore the chain off of the chainsaw and sent it flying! Quite dangerous.

The only thing that's worked so far is to grab each branch and use a hacksaw to get through it. It's just hard to do because of the thorns, so you have to shear off the thorns which is time consuming, since this thing has hundreds of branches all over it.

San Francisco, CA

put a bottle of concentrated round-up on the ground, take a freshly cut end of one of the stems and stick it in the round-up; stake and tie in place so the stem drinks the "kool-aide"...

Municipality of Murr, PA

Another way to kill upper growth is to girdle the branches, scraping the bark off to the bare wood. This will at least stop the flowering. I'd still call these government people (there are phone numbers on those sites) and talk to them and maybe you can have someone come out and look at your monster. "While holding a flame-thrower..."
Dare I say that it could be a "hybrid" of something? That is a scary thought!

When I searched for Mimosa pigra, I looked at the Images that were shown. Some of the flowers were light, almost white. I was mostly looking for that curious ball-of-tufts shape first. It doesn't quite look like Mimosa pudica flowers. Does it have a fragrance at all?

Also if you can buy/borrow a pair of welding gloves, that would help you handle it.

This message was edited Jan 8, 2013 6:02 PM

Benton, KY(Zone 7a)

You might check over in our Australian Gardening forum for suggestions:
They're a pretty knowledgeable group over there and can possibly give you some suggestions.

Merino, Australia

Best thing to do is get some knowledgeable person from the Ag. Dept. to come out .
They should be able to tell you ...(a) what it is and (b) how to kill it.
I have gotten rid of some hard to kill large plants & trees by doing similar to what Vestia says above.
Cut the darn thing somewhere near the base ( I used a tomahawk on a stubborn tree ) then get some pure Roundup into it.

If you know any farmers that use Roundup , ask for a little of theirs.
I find the stuff sold in bulk is stronger.

Hope you can get rid of it but as they say , it can take years.

Good luck

Sydney, Australia

Good luck, if you hear it it yell "feed me" better run.

I wonder what it is.


This message was edited Jan 9, 2013 11:06 PM

Brisbane, Australia

Thanks guys! It's at least given me a place to start out...

The welding gloves might be a good investment...

Prairieville, LA(Zone 9a)

Alex. the QLD Agri, Fish and Forestry department says if you have seen M pigra call them. Since you are not certain of the ID, call them. Here is the number from the link. At best they will be able to ID it and tell you how to eradicate it.

Pest alert

If you have seen this plant

Call us 13 25 23

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