We have recently discovered this one lone Scotch thistle which is a noxious weed in NSW. It grows approximately 1m high and has one stem with many branches, the flowers are purple and have sharp needle like thistles which can cause injury to livestock.
Scotch thistles can be spread by seed which is prolific and is often transported in hay, vehicles and can also survive in the digestive tract of sheep! Gaps in the pasture result in an increase in thistle germination and seedling survival so maintaining excellent ground cover at all times is desirable. Which is interesting because this one immerged by a large pile of dirt which was moved when the shed was being erected.
Goats eat the thistles and reduce seed. Slashing or mowing is not usually effective as plants develop new growth from the base.
More information can be found at NSW Primary Industries