Small world - after puzzling on Tristan's question and getting the answer from Tim , I spot this post elsewhere on another Seseli, from Panayoti Kelaidis ....
Panayoti Kelaidis
"I recall the hue and cry when we proposed
Seseli gummiferum for Plant Select "Nobody can sell biennials!" "Nobody wants white flowers!", "It's too weird for words"...the umbel has had the last laugh: it's a stellar performer at the Gardens, and I see it more and more around the city. And if you stick it in a hot and dry enough spot it often rewards you by turning perennial (for a few years anyway!)...and it self-sows in many gardens enough to perpetuate itself...I (for one) will never be without the Moon Carrot--worth growing just for its names! — at Denver Botanic Gardens."
