Tuesday, 13 August 2013

Wednesday wildflower: Cape weed

Here's something to watch for if you like foraging for wild food: be very careful about misidentifications.  I remember visiting someone in Christchurch once who was carefully transplanting wild hemlock (this one) seedlings into her herb garden, thinking they were angelica.  Well, I shouldn't be smug about that, because yesterday I made a mistake that could have had nasty consequences if I'd been foraging and if the mistake had been in the reverse direction, but I like to think I wouldn't have made it if I'd had a fresh plant or a dried specimen, rather than a photo, to identify.

It was on the Naturewatch website, and someone had posted a photo with a request for identification.  I thought it looked like puha (Sonchus oleraceus), but then I changed my mind and identified it as Cape weed, Arctotheca calendula.  The great thing about Naturewatch is that the identifications are crowd-sourced, and others quickly challenged my identification and convinced me, with evidence, that I was wrong.  The plant was indeed puha (Sonchus oleraceus).  (It's a bit embarrassing, because I wrote the Flora of New Zealand treatment for both these plants.)

So yesterday, I went looking for some fresh material.  Here are the upper surfaces of the leaves:
Cape weed (left) and puha, upper surfaces (scale=1cm)
And here are the lower surfaces.
Cape weed (left) and puha, lower surfaces (scale=1cm)
The Cape weed has more leaflets, a rounded, rather than triangular terminal leaflet, bristly hairs on the upper surface and a dense silvery mat of hairs below (puha leaves are hairless except for bristles at the tips of the teeth on the upper leaves).  Cape weed's leaf stalk is also bristly compared to the smooth puha.

Of course, it'd be hard to confuse them in flower, but early growth is often the time when foragers collect, because some plants get bitter when they run to flower.
Cape weed (left) and puha in flower.
Cape weed is poisonous, but not very, whereas puha is edible.  Check out Johanna Knox's foraging website for information, and always be sure you identify your target.

The moral of the story is that identifying plants from photos can be difficult.  Often the diagnostic characteristics can't be seen and sometimes the colours recorded in a photo don't look the same as in life.  Plant taxonomists (specialists in the classification, naming, identification, and evolution of plants) often refuse to identify photos, but I believe that so long as people understand the pitfalls it's worth having a try.  I really like the Naturewatch site, because it's self-correcting, democratic (everyone can have a go), and we all learn something from participating.

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