It wasn't until I got the magnet home that I noticed there was a bit of a howler on the packaging, repeated on the Natural History Museum's website, which says:
The Tree of Life is the only illustration in Charles Darwin's 'On the Origin of Species'. Darwin used it to show that all things living are related.
Well, not quite.
Although the only image in On the Origin of Species does indeed depict a tree of life, it bears very little resemblance to the one depicted on the fridge magnet, which is taken from one of Darwin's early notebooks on evolution. A facsimile of the notebook is on display at the exhibition (and just to the right).