The Barbican is a sprawling concrete brutality as apt to divide opinion as Marmite or skinny jeans. Built in the 60s and 70s as a housing estate and cultural centre on a vast bomb-site in the City of London, it does not sound like a promising place to go botanising, but after the fire-weed was concreted over, other plants moved in…Aside from the fleabane gussying up the scheduled monuments, and the friendly rivalry of the residents’ window-boxes, the Barbican also houses a large conservatory containing more than 2000 species of plant. It is open to the public most Sundays. A highlight of the conservatory complex is the arid-zone glasshouse, which crams a surprising variety of cactuses and other succulents into quite a small space. Like many botanerds, my sickness started in childhood, when I broke out in a rash of succulents and carnivorous plants – as I enter my dotage, nostalgia grips me and I am drawn back to these plants like a homeopath to idiocy. Is this a botanic garden? Can it be included in my baggings? As far as I’m concerned, the key difference between a garden and a botanic garden is whether the plants have merely been plonked there to be gawped at, or whether the plants are properly labelled with Linnaean binomials and can thus be ticked off a list as God intended: The plants are labelled; Flora be praised; this is a botanic garden.