I guess a "weed" is any plant that grows where you don't want it. If my property was covered in beautiful roses I would still consider them to be weeds as they serve no useful purpose and obstruct my use of the land. We may also be talking about a different plant but using the same name. This is what I'm referring to
From Wiki
It used to do this in Oz
As you can see it would be impossible to do anything with land covered like that.
From Wiki
Prickly pears (Genus Opuntia) are an invasive plant species in Australia.
Prickly pears (mostly Opuntia stricta) were imported into Australia in the 19th century for use as a natural agricultural fence and in an attempt to establish a cochineal dye industry. They quickly became a widespread invasive species, rendering 40,000 km2 (15,000 sq mi) of farming land unproductive. The moth Cactoblastis cactorum from South America, whose larvae eat prickly pear, was introduced in 1925 and almost wiped out the population. This case is sometimes cited[1] as an example of successful biological pest control.
It used to do this in Oz
As you can see it would be impossible to do anything with land covered like that.