Thanks to Jos who sent me a spirit-conserved specimen of a
_Pinguicula moranensis_ pitcher some long time ago (sorry for not
having found the time to examine it earlier!), I can now (I think for
the first time) report on the internal and external anatomy of these
aberrant (teratological) structures:
At its very base the petiole closes around the upper (adaxial)
surface to form a nearly perfect unifacial stalk, circular in cross-
section and with homogeneous single-layered epidermis, 7-9 cell
layers of parenchyma, and a central vascular bundle with almost
circular phloem enclosing the ovoid to pear-shaped xylem. The line at
which the two petiole margins fuse is very obscure, and no obvious
wing is formed. Only the arrangement of some scattered stomata
(indicative of the abaxial surface) along a straight line on the
petiole shows the formerly bifacial nature of the leaf and its
orientation.
The petiole opens into an infundibuliform "pitcher" with stalked and
sessile glands on the interior surface (homologous to the adaxial
surface of a normal leaf). The "peristome" of the pitcher is nearly
circular and somewhat oblique (with the supposedly adaxial pitcher
wall somewhat shorter than the abaxial one). There is no lid or wing
on the peristome.
This proves true peltation (i.e. not lateral margin coalescence) in
the _Pinguicula_ pitchers. The unifacial petiole is very similar to
the stalk of the _Utricularia_ trap. This corroborates the
morphological interpretation of the _Utricularia_ trap as a peltate
foliar organ. It is furthermore very likely that also the traps of
_Genlisea_ are peltate transformed leaves. Almost certainly, also the
sporadically occurring _Genlisea_ pitchers (of which Fernando was
so kind to show me some pictures) are peltate in nature.
Thus, peltation is a general morphological mechanism in
Lentibulariaceae, frequently (with the apparent exception in
_Pinguicula_) involved in the structural design of the traps.
TNX again to Jos, Juerg, and Fernando who supplied me with material
and pictures of various lentibulariaceous pitchers.
Kind regards
Jan