What is a carnivorous plant?

Peter Cole (carnivor@bunyip.demon.co.uk)
Wed, 07 Jun 1995 16:56:07 GMT

Carl Mazur writes:

>I've even heard the argument that S. purpurea isn't carnivorous because
>it's the bacteria that break down the prey, not plant produced enzymes. I
>do believe that to be bogus! regardless of the prey breakdown, the plant
>does absorb the nutrients and benefits from them. Try to keep water in
>them at all times.

Now, this is something that's been bugging me for a while now -
I know it's come up a couple of times in the past, but I can't
recall it reaching any real resolution. What is it that makes a
carnivorous plant carnivorous? If S. purpurea is to be regarded
as carnivorous without enzymes, then why not Roridula, or bromeliads
or Proboscidea, or teasel, or tomato plants (or so on and so on, -
you get the drift.)? Bacterial breakdown must surely ensue in these
cases - bacteria aren't fussy about where they get to work - and the
plants presumably get as much benefit as they would from any other
foliar feed.
Are there special absorption glands in S. purpurea that differ from
the stoma in normal, "non-carnivorous" plants perhaps?
Even if there are, does this make them *as* carnivorous as other
Sarracenias which additionally produce enzymes?

I mentioned bromeliads - well, Brocchinia and Catopsis are now
accepted as carnivorous, but as I understand it (and I'm not a
botanist, so correct me if I'm wrong,) they likewise don't
produce enzymes but rely on bacterial breakdown. Now that's
*really* weird! 2 genera of bromeliads, of which *all* the
species hold pools of water in which, presumably, unwary insects
drown and are rotted by bacteria, (because bromeliads, for the
most part, are like that,) and yet only one Catopsis (bertoroniana
out of 21,) and two Brocchinias (hectioides and reducta out of five,)
are acknowledged as carnivorous.
So what have they got that the others haven't? I don't know.
Perhaps there's an alluring scent, or special absorption glands
again? But even if there are, is that enough? How much is enough,
and who decides? (Jan, I suspect you will have an opinion on this :)
Or then there's Capsella which has the enzymes to be carnivorous
but only when it's a seed. Plants that aren't quite carnivorous
and carnivores that aren't yet plants... it's a funny old world.

I tend to think that pigeon-holes are smelly things fit only for
pigeons. The plants we love are a small and discontinuous part of
the spectrum of plant life on this planet - there are many weird
and wonderful habits and tricks that have evolved to fit localised
circumstances, and of course they are still evolving. I'm not sure
"carnivorous or non-carnivorous?" is the right question - might it
not be more a case of "how carnivorous?"

For the record, I would regard S. purpurea as carnivorous, though
I don't suppose the plants worry about it much. But I also grow
Capsella in my garden (wish I didn't, :-) am waiting for some
Proboscidea parviflora to germinate, Ibicella lutea to arrive and
have a couple of bromeliads (wish they were Brocchinia instead of
pineapple tops :) I've a hankering to try Roridula too...

Happy growing,


Peter Cole | carnivor@bunyip.demon.co.uk | off to spread some cricket
Swansea, WALES | old mailboxes still active | paste on my aspidistra :-)