I'm not sure of the name of this weed but it has a type of bindy prickle type seed pod to it when green. Its the dry, dark seed that I absolutely hate. When in flower the flower is small and yellow. The leaves are similiar to a clover leaf especially when the plant is young.
Now to the not so fun part. If you tread on an old dark seed, and the seed penetrates your skin, your foot will blow up like a balloon, turn red, get itchy, but the toxin doesn't normally go any further than your ankle - well - the swelling anyway. The swelling dies down and your foot returns to normal no more than 48 hours later. In Spring/Summer these older (or riper) seeds are highly toxic.
The weed will grow amongst clover and normal grass. It's seed is dispersed by humans treading on the plants and becoming dislodged elsewhere in the area or further afield. I call it a heavy traffic weed. By heavy traffic, I mean, wherever a human walks daily and even more than once a day. Personally I prefer Scotch thistles and their thorny leaves than these weeds.
That is a weed called burr medic, a real problem for sheep farmers when it gets in fleece. At least it is fixing nitrogen in your soil.
apparently it has some uses incl edible:
http://www.pfaf.org/user/Plant.aspx?LatinName=Medicago+polymorpha
Thanks for id'ing the weed for me, Greg. Honestly, I don't care if it fixes nitrogen into the soil. I've had enough of this weed. Years ago I tried killing it off by pulling the weeds out by hand. 7 years later and I was still pulling the darned things out. I gave up in the end. As I said the dry seeds are toxic, and make my feet swell up. I love walking barefoot at home, even amongst the bees and clover. Now I just try and reduce their numbers in the front and back lawns. I have to be careful where I walk outside when barefoot, as I'm allergic to bee and wasp stings.
I'm at Tenterfield, NSW. (Formerly known as "Hyperbirds".)
For what it's worth, these things are not as bad as bindiis :-/
I try to pull them out by hand too, but it is a near-impossible task to eradicate them.
soakes
Olinda, Victoria, Australia
Many Fabaceae have long-term seed dormancy rendering actual eradication very difficult. they can still be present as seed in the soil for many years whilst the plant is seemingly absent
indeed an internet search revealed reference to this species M. polymorpha seed 200 years old successfully germinate (granted it was extracted from a dry brick, though presumably in soil they can last decades also).
apparently it's also relatively resistant to glyphosate..
Thanks for the link, zosterops. I checked out the seeds to this weed and as it turns out this is not the seed of the weed that makes my feet swell up. The toxic seed in question is about 3-4mm across, somewhat of a curved inward trangle shape and has a pointed spur at one end, and is a dark brown to black colour. You only find it by unknowingly treading on the seed barefoot, or closely looking at the soil whilst pulling out weeds in the lawn. There are no other type of weeds growing in the lawn that would produce this type of seed that I'm aware of. I think I need to find a seed and grow it to find out what the plant is.
If this toxic seed stays in the ground for years, then it only becomes toxic in Spring and Summer. Its the only time of the year when I get done in by these seeds and my feet swell up.
I'm at Tenterfield, NSW. (Formerly known as "Hyperbirds".)
I agree, these weeds are not as bad as bindiis. Bindiis (or as I call them 3 corner jacks) are a weed I don't like treading on either, but as I moved states we don't get them here in Tenterfield, NSW. At least bindiis are not toxic; they just hurt like hell when trodden on.
I'm at Tenterfield, NSW. (Formerly known as "Hyperbirds".)
The best way to control that sort of weed is out-competing it. Use plenty of fertiliser and keep the garden well watered, have lots of healthy ground covers and shrubs,
Greg, just thought you might like to know that these burr medic weeds are mostly infesting the front and back lawns. The odd one grows in the garden which I pull out. They seem to prefer to grow in the lawn than anywhere else.
But these weeds are not the problem anymore. It's the unknown triangle shaped seed which has a spur like end on it that is the problem, and I can't seem to find a plant anywhere on the property that has seed like that. And I've been in these flats since 1998 and have been checking the lawn since then for the plant that grows these seeds but there's nothing. And it's not from an insect that I'm aware of in the grass either. I've checked.
I'm at Tenterfield, NSW. (Formerly known as "Hyperbirds".)