If it looks like a duck and quacks like a duck, then it probably is a duck. So my achira, which looks like a bog standard purple canna, is indubitably a canna, just like the ones gracing a roundabout near you. Mine came with the moniker "achira morada", purple achira. I've had it for years. At one time achira was afforded the honour of species status, Canna edulis; now it seems to be considered a variety of Canna discolor or Canna indica. It comes from - you've guessed it - the Andes.
For some peculiar reason I haven't managed to kill my achira, despite letting it dry out, get frosted and most recently, leaving it in a greenhouse to cook at about 48 degrees Celsius for several days. I wouldn't say that achira thrives on any of this treatment, but it is remarkably tough. I haven't yet tried it underwater, but I've got form, what with the mashua and oca waterlogging debacle last year.
The most shameful aspect of all this is the fact that I have never, despite ample opportunity, actually got round to eating its rhizomes. This year I intend to remedy that oversight. By all accounts they have a pleasant sweet taste and go well with roast guinea pigs, although they take a while to cook - the rhizomes, I mean.
Achira is famed for having the largest known starch grains in the plant kingdom, ones that are visible with the naked eye. It's cultivated in SE Asia, particularly in Vietnam for the production of transparent noodles and also in Australia where it's known as Queensland arrowroot. Because the starch grains are so large, it's easy to grate the rhizomes in water and collect the starch grains with simple home made equipment and produce a high grade starch. My infamous crumpled shirts may be a thing of the past....
I think it might be worth dashing into the local park's undergrowth to explore the edibility of various other ornamental cannas. William Woys Weaver has been doing the same with dahlia tubers, although I think he's growing his own rather than raiding other people's flower beds. Yes, dahlias are perfectly edible. While you're at it, why not try the same with amenity plantings of sweet potatoes such as Blackie, which definitely form useable tubers. Not so much guerilla, as gorilla gardening. You could always beat your chest and pant-hoot if the authorities try and stop you.
Here's my achira, just prior to me lopping off a chunk to send to Frank van Keirsbilck. The keen eyed among you may notice a hog peanut seedling has insinuated its way into the pot. That spell at 48 degrees Celsius seems to have done no permanent harm.
And here's proof, if proof were needed, that this is none other than a canna, with a typical canna's physiognomy:
Those rhizomes look promising, if somewhat stunted and, er, a bit tough. Still, I've eaten mashua and survived, so achira ought to be sweet confection in comparison.
I have eaten other cannas, just not, ironically, my own achira. I can't remember which varieties - too busy dodging the searchlights of the parks dept. The ones I tried had a good flavour but were a bit fibrous. Canadian ones may be better. Good luck with the dahlias and let us know how you get on.