Mohr’s rosinweed (Silphium mohrii). Taken in the one of the glass houses in West Dean Gardens, West Sussex.

I'd never seen one of these before, but I have discovered it is native to the USA and only found in northern Alabama, southern Tennessee, and extreme northwest Georgia. It is considered to be a vulnerable species.

West Dean Gardens have a large collection of plants including exotic plants such as this one.

Better viewed large. Thanks for looking.