The reason they were able to spread so is that the dandelion seeds were able to fly.
If they had not flown away but had dropped down close to the parent plant and grown there, they would not have been allowed to spread much; for people do not like dandelions in their fields and lawns, and try hard to root them out.
This would be easy if the dandelions kept together in patches. But they seem to say “catch me if you can” as they fly on the wings of the wind, dropping down here, there, and everywhere, striking root and merrily growing.
White-headed dandelions.
The parent dandelion takes very good care of its seed children, and plans for their future success by giving each one a little plume by which it can be blown about by the wind.
Everybody knows the pretty, fluffy, white-headed dandelions that come after the yellow flowers.
Seed case and plume
magnified.
Children often blow on them “to see what time it is.” If all the seeds fly away but one, they say it is one o’clock; if two remain, they say it is two o’clock, and so on.