Hi Stephen.
I wes a little casual in my naming of the Apium. The New Zealand plant is known as Apium prostratum subsp. prostratum var. filiforme> so the short answer to your question is that there is no difference. The same variety occurs in Eastern Australia so var prostratum may occur there as well. I do not know. There is a second New Zealand subspecies Apium prostratum subsp. denticulatum that occurs on the Chatham and Antipodes Islands.
As for Lepidium oleraceumthere is a small possibility that I could obtain some seed from my DOC contacts but this may be difficult as it is a protected plant.
Cliff,
I was going to apologise to you as I did not show any pictures of buttercups in my posting but then realised that Myosurus is a buttercup. Does it satisfy your Ranuculophilia?