Re: Pings with pitcher leaves (rather long)

Jan Schlauer (
Thu, 7 Dec 1995 12:52:19 +0100

Dear Jos and Juerg,

>> One of my P.moranensis is forming two peculiar shaped leaves; on a
>> stalk of about 2 to 2,5 cm long there is a pitcher-like leaf of 8 to
>> 11 mm long and 4 to 8 mm wide. Is this normal or is it very
>> extraordinary?
>I have observed (and photographed) several times leaves, where the
>lateral margins were grown together, forming pitchers, in Pinguicula
>vulgaris, grandiflora and longifolia.

This sounds *very* interesting. I think CASPER did report similar
phenomena. The reason why I am interested in this is the evolutionary
course within Lentibulariaceae having led to different trapping devices in
different genera.

> There was always only one leave (in one case
>two) with this abnormality among several normal leaves, meaning that this
>dysmorphy it is not caused by genetical mutation but just by a localized
>growth disorder.

Yes and no. The fact that the phenomenon occurs (rarely, of course, but
repeatedly) in so widely different species shows that there must at least
be some genetic predisposition (of course, the switch to the dysmorphy is
not as permanent as a mutation).

What I would like to know (i.e. to ask you, Jos & Juerg) is if the
"pitcher" is really formed by lateral coalescence of leaf margins
(reminiscent of the pitcher structure in _Sarracenia_) or if it is perhaps
resulting from peltation (like in e.g. _Cephalotus_). This would be
important because presently it is generally assumed that the traps of
_Genlisea_ and _Utricularia_ are formed by peltation rather than lateral
margin coalescence.

The fundamental morphological difference between the two modes of pitcher
formation is visible in the leaf buds and in cross-sections through the
base of the leaves. In peltate leaves, a so-called transversal zone is
formed, i.e. an additional leaf surface on the upper (adaxial) face of the
leaf base. This transversal zone is marked by reversed orientation relative
to the original leaf blade (glands mostly on lower, abaxial surface and
stomata mostly on upper, adaxial surface of the transversal zone). There is
normally no sign of "leaf margin rudiments" along the midrib of the
transversal zone (the only true leaf margins being the apical pitcher rim
and the lid margin). In _Cephalotus_, the pitcher lid +/- corresponds to
the transversal zone. Peltate leaves are formed from unifacial petioles,
i.e. leaf stalks in which the vascular bundles are arranged in a circle
(like in a cross section of a stem), the adaxial bundles with the phloem
oriented towards the adaxial leaf surface.

Pitchers formed from lateral margin coalescence lack a transversal zone. In
_Sarracenia_, the leaf margins are traceable from the very leaf base (where
two clearly visible margins clasp the stem), continuing in the adaxial
pitcher wing (where the two margins are fused), and ending in the peristome
of the pitcher (where the leaf margins separate again) and the margins of
the lid. The leaf of _Sarracenia_ is formed from a bifacial petiole
(showing the normal arrangement of vascular bundles with phloem oriented
towards the abaxial leaf surface and xylem towards the adaxial).

So if it is possible, please try to examine or remember if there are signs
of a "wing" or whatsoever reminiscent of leaf margin rudiments on the upper
(adaxial) surface of the _Pinguicula_ pitchers. It would of course be
excellent if you could prepare some microscopic sections through the
petiole below the pitcher to see if it is unifacial or bifacial. If you are
not able to do so, perhaps it would be possible to prepare liquid preserved
specimens (70% Ethanol) of the pitcher leaves (including at least a small
portion of leaf base *below* the pitcher)?

Thank you very much for your help. I think here we have a genuine chance to
observe evolution "in vivo".

Kind regards

PS: Two additional notes, 1. The recently described _Pinguicula
utricularioides_ (NB!) seems to form subpeltate (the transversal zone being
not very prominent) summer leaves regularly. 2. The partially carnivorous
Dioncophyllaceae and the closely related Ancistrocladaceae do have petioles
which are rather close to the unifacial condition. Both families have
accessory bundles in a circular ("unifacial") arrangement around a central
normal set (which is "unifacial" in Ancistrocladaceae and "bifacial" in
Dioncophyllaceae). Remarkably, no trend to peltation is known in the
Ancistrocladaceae (which would have double predispositions for it,
anatomically). Perhaps _Ancistrocladus_ is a pitcher plant when nobody
observes (or collects) it... ;-)