In the paper by JAFFE, MICHELANGELI, & al.: "Carnivory in Pitcher Plants of
the Genus _Heliamphora_ (Sarraceniaceae)", New Phytol. 122:733-44 (1992),
it is stated on p.739 that the water in the pitchers of _H._ have a lower
water tension than that from nearby ponds or bromeliads. Indeed, their
experiment was very similar to yours: they dropped ants into the pitchers
and measured the time the ants were able to swim on the water surface. The
surfactant wasn't identified, however. No species is referred to, but on p.
734 in discussing the whole genus the same is repeated. So I assume it is a
generic trait for _Heliamphora_.
Andreas, I wrote in a reply to you:
>(...) nor does it seem too probable that _H.nutans_ (which may have pitchers
>>rather similar to those of the Tramen-tepui plant) should have reached the
>>Ilu-massif.
Until yesterday, I laboured under the mistake (inexcusable, again!) that
_H.nutans_ and _H.ionasii_ were allopatric species. This is of course
almost complete nonsense as I see now, after having read MAGUIRE more
thoroughly. Their geographic ranges do overlap completely, only _H.ionasii_
being somewhat restricted to the north.
_H.nutans_ DOES DEFINITELY OCCUR on Mt. Ilu-tepui (cf. e.g. a collection
made 1952 by MAGUIRE, no. 33379), and these populations are almost
continuously connected to others reaching as far to the south as Mt.
Roraima.
This changes the world for me.
Under these circumstances the high probability of introgression (by
_H.nutans_) must be considered, and you=B4ll almost certainly run into big
trouble and lenghty discussions if you try to establish a third (sympatric
and ill differentiated) species for this region. I=B4m quite convinced now
that the _H.nutans_ like plants from the Ilu region are indeed _H.nutans_,
maybe vars. different from the type, but rather certainly NOT ANOTHER
SPECIES. Other, more _H.ionasii_ like plants could represent atypical vars.
of this species or even hybrids.
Anyway, I must hasten to mention that I'm not sufficiently familiar with
these populations to judge their relationship or variability
satisfactorily.
Kind regards and sorry for the confusion
Jan