Floriferous London

My weekly botany course is coming to the end of term. Taught by the wonderful David Bevan - a former conservation officer who is a curious, gentle hybrid of David Attenborough and Patrick Moore; we convene on Monday afternoons in Highgate to hear his stories of the plants that live alongside us.
So what have I learned?
To name and love those rogue weeds that appear in my garden. It sounds so much better to say that herb robert, herb bennett and gallant soldier are colonising my tiny borders.
That plants are valued for their ability to survive. And in London's landscape of disused railways, building sites and crumbling edifices, there is a whole parallel botanical world. Here, plants are economic migrants, blown, flown or transported in from different climates; they adapt to their new surroundings: buddleja is a native of cliffs in China, so think of it in a new light when you next see it sprouting from a wall or roof; they eventually even sound quite English: Oxford ragwort is Sicilian in origin and loves to grow in the klinker between railway tracks - it's like the volcanic ash of home.
That these wild London plants usually have some cracking good stories to tell: Gallant soldier is also known as Little Joey Hooker (after Sir Joseph Hooker who founded Kew Gardens...); Haringey Knotweed is a unique London hybrid - a cross between japanese Knotweed and russian vine - that inhabits, quite exclusively Railway Fields, just off Green Lanes (although was once found in a gutter in Crouch End); London Rocket, another mediterranean interloper, was first identified by 17th century botanists when it grew strictly within the City of London boundaries, only to disappear mysteriously in the 19th century - and return after the second world war.
And, next time I'm in the area, I must look out for the maidenhair spleenwort that favours the wall outside The Odeon at Muswell Hill.