Echium pininana is naturalising in warmer parts of the UK, including London. This exotic arrival from the Canary Islands is often referred to as Giant Echium or Tree Echium, both names are apt.
 There is a colony of them in St. James' Park in the heart of central London. The photo above demonstrates the triennial lifespan of E. pininana. The bright green leaves at the front are the first year's growth when the seedling puts on a rosette of leaves. The darker green leaves behind are plants in their second year with a thick stem that grows to about a metre tall. In their third year a tall spike forms covered in thousands of blue flowers in early summer. The plant then withers and dies shedding masses of seed as it does so. The shriveling stalks are what remains by this point in the year.
 The photo below shows the same locale when the Echiums are in flower, it's quite a sight:

 I have wondered whether the ones in St. James' Park are a chance arrival that has spread or an introduction. Walking in the park yesterday I spotted one of the park gardeners doing some watering. I asked him this question and in fact it was he who first planted them! He started with half a dozen and they have self-seeded to the point where there are many. Well done that man!