I always get lots of inquiries at this time of year about this "terrible weed that is taking over my paddocks". People are inevitably talking about Fat Hen (Chenopodium alba), also known as White Goosefoot or Lambs Quarters.

I am no stranger to this plant, as the photo below shows. My first property as a single Mum
was extremely run-down and had more Fat Hen than grass

The reason that it looks like it is taking over is that it is an opportunistic plant that germinates in bare ground after any summer rain. Pastures are normally pretty dry and dormant, but this little forb is in its element. It takes advantage of any bare ground where it germinates quickly. It is almost the summer version of Capeweed, but the advantage with Fat Hen is that it is not outcompeting pastures during their growing phase.

The entire plant has a distinctive white mealy covering, which is even present as a seedling.

Flowers are inconspicuous, greyish-green without petals.
They occur in dense mealy clusters at upper-leaf junctions and stem ends.

As an indicator plant Fat Hen loves to grow in soils that are high organic matter, such as sheep yards and stock camps beneath trees. These sites also provide the high nitrogen levels in which it thrives.

Fat Hen is an interesting plant. Historically it was used extensively as a green vegetable before spinach (from the same family) became popular. It is exceptionally high in minerals, containing many times more protein, calcium, phosphorus, vitamin C, vitamin A, and iron than spinach.  

Fat Hen seed is also used as a grain before quinoa (also from the same family) was recognised as a superfood.

Most species in the Chenopodium genus have the ability to accumulate oxalate and nitrate. But field cases of poisoning are rare. It contaminates cereal grain harvest and taints milk

The seeds are particularly resilient, believed to remain viable in the soil for up to 30-40 years. They also survive the silage making process, and survive digestion by cattle.