There is another way to think of plant escapes: when I lived at Kew, there was a story about ‘bid for freedom of plants from Kew’ – Giant Hogweed (Heracleum mantegazzianum), growing up to 7m tall, had been found in a neighbourhood garden. The Evening Standard had a memorable cartoon of it climbing the Kew wall and boarding a 27 bus. Seriously, though, such ‘invasive aliens’ are a major problem, with alien species being introduced by people and devastating the local flora and fauna. An interesting paper by Osunkoya et al. from Queensland, Australia, in the August Annals of Botany, discusses the data that successful invasive species have more efficient carbon fixation strategies than native species they displace.
Using the search box, above right, with “invasive aliens” will show we publish something like 10 papers a year about this ecological group of species.
Meanwhile, escapes from greenhouse roofs are not unique to Kew: these pictures show another species of Agave, A. americana or the Century Plant, growing up and escaping through the roof of the greenhouse at the University of Leicester Botanic Garden, a few years ago. Although the common name suggests it only flowers once in a 100 years, actually the plants flower after a rather shorter time.
O. O. Osunkoya, D. Bayliss, F. D. Panetta, G. Vivian-Smith, 2010, 'Leaf trait co-ordination in relation to construction cost, carbon gain and resource-use efficiency in exotic invasive and native woody vine species', Annals of Botany, vol. 106, no. 2, pp. 371-380 http://dx.doi.org/10.1093/aob/mcq119