On a Wild Flower Society trip to Ham River Lands we wanted to see the well known site for Hieracium speluncarum (Cave Hawkweed) so entered the National Trust's properties at Ham House. Having found the Hawkweed very easily we decided to look in the cultivated gardens for weeds. As long as the gardeners are a bit lax you can find some excellent specimens of weeds in gardens and allotments because the soil is so fertile. Having recorded about ten of the usual suspects we came across one specimen of an umbellifer which no-one recognised.

Consulting a nearby notice board describing the herb garden, it said they they had once grown Sium sisarum (Skirret) as a root vegetable and illustrated the very plant we had found. It was grown as a substitute for Parsnip or Carrot in the 15th century and was known as Skywort in those days. It is still grown in the United Sates and in some countries as a substitute for Sweet Potato. It wasn't being cultivated in these gardens and looked a little sad at being so neglected. Privately I was quite pleased at my attempt at identification because I suggested that the nearest thing I'd seen with leaves like that was Greater Water Parsnip (Sium latifolium): the same genus.

S. sisarum isn't on the B.S.B.I. list, nor in Kent, nor in any edition of New Flora of the British Isles by Clive Stace neither can I find it in any book I've got in my library but there is a blog about it and how to cook it:

About Skirret 

Distribution: Sium sisarum is never found anywhere at anytime under any circumstances in the British Isles - except here at Ham House very occasionally.

Possibly this is the rarest plant in Britain. Even its name has been erased from the lists and learned journals.

Weed in herb garden at Ham House, London 7th July 2007

Added on 23rd February 2008, updated 9th February 2012