Chamaele decumbens vegetable

[Richard Wright]

Does anybody know a green vegetable/herb with the scientific 
name Chamaele decumbens or Sium decumbens? It is a member of 
the Apiaceae (ex Umbelliferae) or celery family.

I am trying to identify a herb being wrongly sold in Sydney 
as Lebanese Cress (Aethionemum cordifolium).

The plant in question has pinnate leaves, inconspicuous 
umbels of short stemmed white flowers, and a vigorous 
sprawling habit due to spreading runners. From some initial 
research I suspect it may be Chamaele decumbens of Japanese 
origin, but can find no illustration or description.