Hybrid mint

It's not always easy being a botanist. As well as learning characteristics of all the individual species, you also need to be able to recognise the hybrids, which can be mindbogglingly difficult in some cases.

I'd seen a lot of corn mint in parts of the Great Fen, a species with whorls of flowers all the way up the stem and no terminal spike. Its leaves smell rather unpleasant to me. But yesterday I came across this, which superficially looked similar, but was a bit taller, with deeper purple flowers and definitely had a more pleasant odour. Having examined it closely today, I've  confirmed, from the characteristics of the calyx and the fact that it's largely infertile, that it's the hybrid between corn mint and water mint, which goes by the catchy name of Mentha x verticillata. Apparently a new record for Holme Fen NNR and the hectad its located in.