Unknown ?? Cucurbitaceae ??

[Lvandelft]

A Dutch gardener/nurseryman found in his Dahlia fields this plant.
And he would love to know what it is. He told me that it forms a rather big roundish tuber.
I really do hope there is somebody in this super knowledgeable Forum who can tell more.

[Maggi Young]

a rather big roundish tuber

a tuber?  as in an underground tuber  ?

[t00lie]

Just a guess

Wild turnip or a member of that family .

Cheers dave

[Lvandelft]

Yes Maggi an underground tuber.
We were thinking of Bryonia but the Bryonia's here in the dune areas have different leaves.
But the tuber would fit probably.

Just a guess
Wild turnip or a member of that family .
Cheers dave

Oh Dave, I had first to look up what turnip is , but that it is surely not. No Brassica at all.

[kirsitn]

I don't know what it is, but I don't think it's a Cucurbitaceae - at least I've never seen any Cucurbitaceae with "wings" along the leafstalk.

[Diane Clement]

It looks like a Chenopodium (album or bonus-henrici) or Tetragonia?.  But these don't fit with the tuber? 

[Afloden]

It is Asteraceae. Look up the genus Polymnia. I'll bet that that is what it is. There are a few Mexican species and three in the US. I grow two of them. There are tubers in P. uvedalia (syn. Smallanthus) and some thick roots in canadensis. Was he growing wild collected Dahlia seed?

 Aaron Floden
 University of TN Herbarium

[Maggi Young]

Well done, Aaron!
Luit, here's a link to a page about Polymnia sonchifolia.... in Dutch! http://www.wur.nl/NL/onderzoek/Wetenschapswinkel/Projecten/yacon/

[Lvandelft]

Thank you all for taking time and look at the picture.
Aaron it is indeed a Polymnia. I just had the man on the phone who told me that
the tubers are exactly looking like the one on the Website which Maggi put in her posting.
Maggi it's strange but when I googled Polymnia I did not find this Dutch site.
But I discovered on this site that there is another Website in English too.
There the plant Polymnia sonchifolia is said to be Polymnia edulis and P. sonchifolia is a Synonym.
Here is the address and it is very interesting reading!

http://www.pfaf.org/database/plants.php?Polymnia+edulis

Interesting too is that the man on the phone told me that his tubers were between imported Dahlia tubers
from UK last winter. There were 4 of them and he got 2 of them.
 
THIS IS REALLY A WONDERFUL FORUM!! So many nice and knowledgeable people.