Re: Brocchinia

Jan Schlauer (
Tue, 8 Feb 1994 11:04:57 +0100


>What are your criteria for judging carnivory?
>I thought the classical criteria (Darwin, Lloyd?) were something like:
> 1) Attracts prey: (scent, color, nectar, etc)
> 2) Has specific adaptations to trap prey:
> (pitfall, clamshell, flypaper, etc)
> 3) Has adaptations for utilizing prey
> (digestive enzymes, symbiotic fungi, bacteria, etc).
>According to these criteria, _Capsella_ would appear be carnivorous.
>Its seeds chemically attracts mosquito larvae, traps them in mucilage,
>and it can be demonstrated that the seed is beneficially affected by the
>absorbed nutrients.

Do you know _Capsella_ in the field? Here, it is a tedious weed in almost
every habitat suitable for terrestrial plant life. But its seed almost
*never* gets into contact with mosquito larvae (living in standing or
slowly running water; _Capsella_ is not a water plant!) in vivo. Nor does
it normally trap or digest animal prey (yes, there may be occasional
exceptions). There is no obvious ecological pressure urging _Capsella_
seeds to use additional food sources.

>Similar arguments can be made for some of the others on your list, like

Yes, indeed, and they are similarly unconvincing!

>Others fail the test: Roridula does not have glandular, digestive
>secretions and does not appear to absorb nutrients from prey

Yes, that is essentially correct. However, eventually the nutrients are
absorbed via the roots when prey (or digestion products of specialized
symbiotic animals) falls down; this is of course not carnivory in the sense
we have in mind. You remember I do not think _R._ to be carnivorous, don't

>_Solanum_ again has sticky hairs, but no direct absorption, etc.

I am not completely sure if _Solanum_ *never* has absorption. I do not
think this has ever been examined systematically (I may be wrong in this
respect). But nevertheless, I do not count the Solanaceae with cp.

>I'd be interested in where you draw the dividing line?

I have two (= no!) answers for you. The problem is to draw dividing lines
in a continuum. A typically human concern, but we cannot help being human
beings, can we?

The simple (rather dogmatic ;-)) answer is:
As far as known (i.e. to me), cp are all phanerogamous plants belonging to
one of the following genera and all plants belonging to the following
genera are cp, all other living beings (whether animal-consuming or not)
are *not* cp:
_Heliamphora_, _Sarracenia_, _Darlingtonia_, _Cephalotus_, _Drosophyllum_,
_Dionaea_, _Aldrovanda_, _Drosera_, _Nepenthes_, _Triphyophyllum_,
_Byblis_, _Pinguicula_, _Genlisea_, and _Utricularia_.

The more sophisticated answer:
There is *no* dividing line because there is no conditio sine qua non for
carnivory in plants. It is a syndrome rather than a point mutation, and it
certainly has evolved (and *is* evolving, of course) at different times
from very different lines.

Being a primitive (=human) person, I just prefer the primitive version.

Kind regards