There are a lot of sidelines to the Seedbank's work, all of which seem to have just grown (excuse the pun) from their original premise of saving seed from every plant in the world.
Now they not only collect rare seed: they germinate it (sometimes in very complicated ways) and grow it on to re-patriate it. These are seriously rare plants - six are entirely extinct in the wild - and it's not long before you're looking at a lot of seedlings of plants you've never even heard of before.
You might remember reading about it in 2006 when it was found, tucked into a notebook owned by Dutch merchant Jan Teerlink and left, forgotten, in the National Archives at Kew. They'd been there for over 100 years. Yet despite their hair-raising journey - the ship they were on was captured by the British Navy - some of the seeds were still viable, and this, two years on, is the result.
Here's another one: this is a Banksia brownii....
...also known as a feather-leaved banksia (you can see how it got its name). This is critically endangered in its native Australia, with only two or three populations left in the wild. The Seedbank is growing on dozens of them in its cool greenhouse ready to go back home. One batch was returned last year: without this work the plant would be extinct within a decade.
I did recognise one plant there - this protea, just about to flower, is from wild populations on the Cape. The Seedbank works almost exclusively with wild populations - if I understood right, it's because the lineage is purer, and seed from cultivars rarely comes true in any case.
Looking at these plants standing in rows on benches in the greenhouse, they look entirely normal and unremarkable. But these individuals at the forefront of survival for many species: without them their kind would simply die out.
You may be tempted to think that while that might be regrettable, it doesn't really amount to a hill of beans in the grand scheme of things. But bear in mind that not one of these plants has been tested to find out what illnesses it can cure, or what useful purpose it can serve. Not that every plant has to have a purpose - but as was pointed out to me, a few years ago we didn't know that daffodils contain galanthine which they now use to treat Alzheimers. So if we let any one of these plants die out, we could be throwing away chances we wouldn't even know we might have had. That's as good an argument as any, if you ask me.