Hydrangea

A hydrangea was a type of plant. Maebh Arden's mum complained to her ex-spouse that she couldn't see inside her house because the next door neighbour had planted some. What she didn't know at the time was that the whole of London, and indeed Earth itself, had been rapidly afforested overnight. At the end of the episode, Maebh's missing sister is revealed when the hydrangea burns off. The sister's name is Annabelle and the variety of hydrangea she is hidden in is also named Annabelle. (TV: In the Forest of the Night)