clover like thingy wouldn't be wood sorrel would it? Oxalis europea http://www.britannica.com/EBchecked/top ... ood-sorrel
It is in any pot you get from almost any nursery. In my native nursery my daughter dehydrated it and reconstituted it .. and it grew.
Very few plants can be laid out in 40+ temps in the sun all day then watered at night to see them alive the next day. This species seeds prolifically and any portion you leave behind when weeding is just like planting cuttings of it. You have to remove all the root.. It is a runner type which though torn up will leave running roots under the top 50mm of soil. Glyphosate takes it out but the seed is everywhere. However. Even though I ran a nursery in my back yard. My yard is to this day fairly clean of Oxalis. Though it still pops up in forgotten corners. When I see it I attack it before seeding starts. Like burr medic it will try and kill out your lawn.
There are several species of Oxalis wild in Australia. The bulbous type being fearfully invasive and difficult to despatch. Mix a strong solution of urea and spray it on the leaves. If you dare to dig it.. Do it in early spring before the bublets disperse from the tap root.
I have battled nutgrass and convolvulous.. and Tagetes minuta the latter which useful for combatting nematodes is a nightmare once it starts seeding in your garden. Is capable of growing and seeding on the slightest rainfall Therefore difficult to remove from bushland once it is out there.
Thankfully I have never deliberately spread a weed native or non-native.
I always compost prolific weeds.
Caltrops. A non-native inhabitant of most of Australia. pull them out in the first two weeks after germination or .. get seed by four weeks. Seed can last decades so you definitely don't want that. This is another weed which will grow in the most arid desolate places on a few spits of rain occasionally. Though galah's love to eat the seed there aren't enough galahs to eat it out. If a rain causes some to germinate and you don't kill it before it seeds there will be literally millions of seed. Whenever they get away from me I roll out the wheelie bin and wear a pair of NEW.. rubber thongs.. The spikes will go through worn thongs. I then walk all over the affected area stand on each foot in turn and scrape the other thong into the wheelie bin.. repeat until no more catheads adhere to the thongs.
Anyway as has been suggested; a weed is simply a plant in the wrong place..
A lovely flowering Eremophila is called Poverty Bush by those who see it as a sign of a failing farm. Blame it as a woody weed and try to eradicate the only plant that has a chance of helping the farm survive.
_ Any plant will grow from a single bud if you can replicate the required circumstances.