Update 19/07/10: The mystery is solved!
Just the other day I was wondering if I'd ever find out what this plant was. Then yesterday I got an email from my son's good friend's father who is a botanist. Why had I never thought to ask him before? Especially as it turns out he is actually one of New Zealand's Brassicaceae experts!
So, thank you Phil Garnock-Jones for this information:
Your mystery Brassica is Brassica fruticulosa (Mediterranean mustard); within that species it belongs to subsp. mauritanica, so it comes from North Africa. It's common around Wellington as far as Palmerston North. The wrinkly seed pods and the stalked upper leaves help to identify it.
I will write a new entry for it soon. (And more info about it is here. Thanks Phil for the link.)
Also - thanks - and a HUGE apology to Mike who wrote a comment here a few months ago (see below) that I never saw until today! He had solved the mystery already - 'twiggy turnip' is a common name for Brassica fruticulosa.
Here's a plant that looks a lot like wild turnip - and for the longest time I thought it WAS wild turnip ... until a visit to a helpful botanist and forager put me right. (Thanks Julia!)
It's in flower all round Wellington at the moment. The flowers are slightly paler than wild turnip flowers, but are otherwise very similar. Like wild turnip, the flowers open above the bud, rather than below it. (Some Brassicaceae do the opposite.)
The leaves have quite a different shape to wild turnip leaves, with more rounded, curvy edges, and a smoother feel. They also don't grow so large as wild turnip, and when they go to seed, the seedpods are noticeably smaller.
What is this mystery Brassicaceae? If anyone can help, I'll be grateful.
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