Updated November 21, 2005 at 12:09pm: Changed the common name based on Maire's comment below – thanks, Maire! Also, read Brent Hine's comments below re: the name discussion from the entry.
Commonly called “bidibid” or “piripiri” by New Zealanders, the species Acaena magellanica is native to both New Zealand and Patagonia. This particular plant is labelled as variety laevigata in the Australasian section of the Alpine Garden. This warrants some investigation, as I think that variety laevigata is strictly South American (so either the label is incorrect, the identification is wrong or the plant's been in the wrong bed for a long time – since 1983!) .
I thought I discovered the perfect paper to supplement this entry: Lee et al., 2001. Fruit features in relation to the ecology and distribution of Acaena (Rosaceae) species in New Zealand. New Zealand Journal of Ecology 25(1): 17–27 (or direct link to the PDF article). As it turns out, they don't cover two of New Zealand's nineteen species of Acaena in the article, and Acaena magellanica is one of them. Still, it's worth investigating. Keep in mind while reading it that this Acaena is in the Section Ancistrum, or “spined fruits with barbs” section – I suspect similar conclusions can be drawn about Acaena magellanica as are drawn about other species in the same section.
Botany resource link: Adaptations and economic uses of rainforest plants via the Missouri Botanical Garden.
Acaena magellanica -Z6, RHS Index of Garden Plants, Griffiths
Yes, Daniel, you're right on one of the above counts: this plant has been in the wrong continental section for a long time. It has recently been confirmed as Acaena magellanica subsp. laevigata. A piece of it will likely be moved into the South America section and the rest removed from the garden. These burrs are really striking and have the annoying habit of really sticking onto shoelaces when walked through - a sure way to spread seed.
"Commonly called “bidbid” or “piripiri” by New Zealanders,"
I don't really know about *all* New Zealanders, but "bidbid" is not used in my experience. I think you meant "bidibid".
Get rid of it while you can!
It (or at least the very similar-looking Acaena novae-zelandiae) is proving a dreadful invasive weed in parts of Britain - worst in coastal sand dunes.
I suppose there are actually advantages to our dreary, wet winters in Vancouver. Seeds such as these do not generally overwinter. This species is not weedy locally, nor are any other acaenas, as far as I know.