In article ,
Mike Lyle wrote:

I never cease to be surprised at how slow plants seem to be to spread
across land-masses, even allowing for deserts and mountain ranges.

Well, yes and no. It depends critically on HOW they spread. Ones
carried by wide-ranging birds or high into the air by the wind have
been ubiquitous since time immemorial.

Nettles, oxlip etc. spread by seeds falling under gravity, and so
will move slowly. Only the occasional one will be carried further
by mammals or birds.

Black nightshade, on the other hand, is spread by many species of
birds and is ubiquitous.


Regards,
Nick Maclaren.