I'm still not totally sure how critical enzymes are for digestion.
Could not a case be made for purely bacterial digestion if it was
widespread and constant enough? - eg: if bacterial activity
occurred ubiquitously within the traps of a certain (hypothetical,)
species, and was brought about by bacteria broadly of one species/
mix of species in the traps of all specimens. Combined with a
trap capable of attracting and catching insects, and absorbing
the resulting nutrients, the result would not be so dissimilar
from S. purpurea (except that I know nothing of the bacterial
distribution specific to S. purpurea - that's why I'll stick
with "hypothetical".)
I imagine the proposed case for Brochinia and Catopsis proceeds
along these sort of lines - tank-fluid odour attracting insects,
a distinct, slippery/scaly zone situated where insects may best
succumb to gravity, and absorption of the rotting remains by
the leaves - I don't know how much research has been carried
out on the nature of the bacterial action, nor on the absorption
mechanism (though foliar feeding is hardly an unusual concept.)
I would guess the objections run deeper than observed behaviour,
based on more complex botanical factors that I don't (yet) fully
understand - I still can't see a fundamental difference between
the case of S. purpurea and Brochinia. It seems a very hazy
line between carnivorous plants and non-carnivorous plants to me.
Fernando, you mentioned an insect-confusing 'trick of the light'
observed in Catopsis - do you know any details of this? It sounds
rather curious...
...
> Next come the Sarraceniaceae (some of which lacking proteolytic enzymes),
> but the family being evidently of monophyletic origin, and the trapping
> device being of a remarkably uniform structure. As the family does contain
> some "complete" cps (fitting the above cited criteria) in two of three
> genera, I am still tempted to call the whole family carnivorous s.l..
Which leads me to ask - does a whole genus or family have to be
deemed carnivorous because it contains carnivorous species? Or
to put it another way - is it necessary that all species in a genus
(or genera in a family,) should be demonstrably carnivorous in
order to classify a/some species as such? I sort of wonder if
this is not perhaps a partial factor in the lack of acceptance for
species such as Brochinia and Catopsis - they would be (if they
were carnivorous,) the first (that I've seen,) species sharing a
genus with demonstrably non-carnivorous species... but I haven't
read the publication of their supposed feeding arrangements, so
they may not be the best example of this.
Oh, and "two of three"? Did I dream it, or didn't someone find
enzymes in Darlingtonia recently? That would surely make three
(and tidy up the aesthetically messy situation at a generic level.)
> Then come non-cps which approach cps from some side (bromeliads,
> _Roridula_, _Ibicella_, _Dipsacus_, _Lathraea_, and many, many more), all
> of which lack at least (own!) proteolytic enzymes (there are rumours
> however that _Ibicella_ does have them, but I have not seen any of the
> proof, and then there is still the question of resorption).
If the plants have gone to the trouble of evolving enzymes, I
should think they must also have developed the means to make use
of the resultant nutrients. Else what advantage to sustain the
characteristic in the face of ongoing evolution?
> An finally, some very few examples of plants are known (e.g. _Poa annua_,
> _Lemna minor_) which do (perhaps) not fit any of the criteria necessary to
> be called a cp.
Maybe these are the most unusual plants then! Perhaps there
should be an _International Non-Carnivorous Plant Society_ devoted
to the study of wind-pollinated grasses and pondweed :) (I'd guess
most algae fits the bill as non-cp also.)
> So in this concept Saraceniaceae are already on the borderline (or rather
> border-zone, there are no clear cut lines, v.s.), and Bromeliaceae and
> _Roridula_ are already far beyond. These plants could perhaps be called
> "subcarnivorous" (they have some of the adaptations needed for carnivory
> but lack some others), another term "precarnivorous" sounds too
> teleological (we can not really predict the course of evolution), and
> "hemicarnivorous" suggests that the others were "holocarnivorous" plants
> (i.e. completely heterotrophic, without chlorophyll in analogy to
> holoparasitic plants), which have not been discovered yet.
Perhaps there's a holocarnivore out there waiting to be found -
(now that I'd like to see!) Though I dread to think of the
environmental conditions necessary to promote such a thing unless
it could arise from albino mutations or somesuch.
Happy growing,
Peter