Phylogeny of Carnivorous Plants
Updated September 9, 2006
Phylogenetic systematics attempts to
construct a classification of organisms that reflects descent.
Molecular genetic research in the past 10 years has greatly enhanced our understanding
of evolutionary relationships among angiosperms. Molecular
phylogenetic analyses continue to
provide quantitative data for objective inference of angiosperm phylogeny,
largely eliminating room for subjective interpretations that have resulted in
differing taxonomic views in the past.
Molecular systematics relies on gene sequencing which allows the determination
of the exact sequence of nucleotides in DNA and RNA. Coupled with the modern computing power for the subsequent analyses
utilizing the cladistic approach, phylogenetic relationships among targeted organisms
are probabilistically inferred.
Radically revising the traditionally
accepted classifications, all nineteen currently recognized carnivorous plant
genera are now placed in five taxonomic orders, confirming that the transition
from non-carnivore to carnivore had taken place in multiple lineages of
angiosperms. The molecular approach also suggests that, in the order Lamiales, carnivory was
acquired independently in three families. It would
mean that carnivory has arisen at least 7 times in the course of angiosperm
The chart here is a pictorial rendition
of angiosperm phylogeny (APG II. 2003 and others), with the currently recognized
carnivorous plants expanded to the genus level.
Rather isolated from the rest, the order
Poales (belonging to monocots)
contains carnivorous plants possessing a primitive pitfall trap (Paepalenthus,
Brocchinia, and Catopsis).
water-retaining tank is formed by tightly overlapping leaves in the rosette
center. The leaves surrounding the tank are coated with loose, easily detachable
waxy powder that causes an insect to lose its foothold. These
sometimes only regarded as quasi-carnivorous because of the primitive nature of
their trap and the lack of digestive enzyme secretions.
Phylogenetic analyses of DNA sequences
have placed Droseraceae (Drosera, Dionaea, and Aldrovanda),
Nepenthaceae (Nepenthes), Drosophyllaceae (Drosophyllum)
and Dioncophyllaceae (Triphyophyllum) in the
same order Caryophyllales.
A traditionally accepted close relationship among Drosera, Dionaea, and Aldrovanda
primarily on floral and pollen morphology has been favorably
supported in molecular systematics.
Sundews (Drosera) cover their
leaves with sticky, mucilage-tipped hairs. Their hairs, often referred to as
tentacles, are not a simple, single-celled hair. They
not only have a multi-cellular stalk, but also possess
epidermis as well as vascular systems in the stalk center, as if tentacles
themselves are a miniature leaf.
Dionaea and Aldrovanda
both possess a snap trap, the most advanced prey trapping mechanism to be found
among carnivorous plants. Although Dionaea is a land plant while
Aldrovanda is aquatic, they share a great deal of common features in their
snap trap mechanism. The traps have a terminal leaf blade that is divided into
two half-shell shaped lobes connected along the midrib. Both traps have
sensitive trigger hairs on the inner lobe surface that initiate a swift trap
closure when stimulated.
Molecular evidence shows these species
are closely related, with Aldrovanda being sister to Dionaea,
suggesting a common ancestral origin of these snap traps.
Furthermore, Dionaea and Aldrovanda form a clade which is sister
to Drosera. This strongly supports a speculation that Dionaea and
Aldrovanda evolved from a common sundew-like ancestor.
Without any fossil records revealing a
hint of intermediate forms, how an ancient adhesive trap developed into a snap
trap remains unknown.
tentacles are divided into three groups based on their behavioral
characteristics: marginal tentacles, outer tentacles, and central tentacles. The
marginal tentacles grow around the perimeter of the leaf blade and are the longest
of all tentacle groups. When directly stimulated, the marginal tentacles bend toward
the center of the blade (nastic motion), but does not transmit stimuli to other
tentacles. The central tentacles, when stimulated, do not move, but transmit
stimuli to other tentacles. Venus flytrap's guard hairs that surround the trap
lobe margin are observed to possess xylem in the center, as in sundew tentacles.
It is possible to speculate that the Venus flytrap's
guard hairs correspond to the marginal tentacles of sundews, while the sensitive
trigger hairs came from sundew's central tentacles.
Mutation is likely to have played a role in the
development of the snap trap.
contains close to 100 species of tropical pitcher plants from the Old
World. The plants develop a pitcher at the tip of a long tendril extending
from the midrib of a regular shaped leaf (morphologically, the leaf base).
The ancestor of Nepenthes is speculated to be a sundew type plant.
The branch leading to Nepenthes has further developed into
Drosophyllum which produces sticky glandular leaves, like Drosera.
The carnivorous feature
then seems to disappear and stay dormant for a while, only to re-emerge in
Dioncophyllaceae. The monotypic genus Triphyophyllum is a tropical
liana, somewhat reminiscent of Nepenthes, but with slender, adhesive
glandular leaves, quite similar to those of Drosophyllum. In
Triphyophyllum, these carnivorous leaves are produced only seasonally,
and only in the young plant before it enters the adult phase of a climbing
The adhesive tentacles
of Drosera, Drosophyllum, and Triphyophyllum are all
multi-cellular in structure, possess the xylem in the stalk center, and are
far more complex than a typical hair commonly found in plants.
It is as though, with
the acquisition of an adhesive trap
trait in the common ancestor of Drosera
and Nepenthes, the order Caryophyllales has been predisposed to
genetics research suggests that in the order Lamiales the transition to carnivory had
taken place independently in the three families, Lentibulariaceae,
Martyniaceae, and Byblidaceae.
contains three genera, each having a morphologically distinct trap type. Two
of these, Utricularia and Genlisea, are closely related, both
possessing a unique and complex underwater trap to capture tiny water
The other genus
Pinguicula has developed an adhesive trap. The surface of the
butterwort’s leaf is covered with numerous hairs tipped with mucilage
secretions. These hairs are a simple, single-celled hair supporting
multi-cellular glands at the tip that produce adhesive mucilage to trap
Martyniaceae (Ibicella) and Byblidaceae (Byblis) have both
developed the adhesive trap similar to that of Pinguicula. The hairs
of Pinguicula, Byblis and Ibicella (having a
multi-cellular stalk) are a simple hair, commonly found in many other
plants, and do not possess the complexity of sundew tentacles.
The carnivorous plants
in this order produce a zygomorphic flower (bilaterally symmetric) though in
Byblis it is only partially so.
comparisons have placed Sarraceniaceae and Roridulaceae in the order
Ericales. The New World pitcher plant family Sarraceniaceae contains three
genera, Sarracenia, Darlingtonia, and Heliamphora. In
terms of their pitcher formation, all these pitchers are a rolled leaf
with opposite margins fused together, quite different from pitchers of
has developed sticky leaves with powerful glue of resin. The plant resembles
in shape some species of Drosera, but the similarity is more apparent
than real. Roridula’s adhesive trap differs from other
traps in that the secretions is resinous, distinct from water-based, mucilaginous
adhesive traps found in other carnivorous species.
an Albany pitcher plant from Western Australia, is placed in the order Oxalidales.
The Cephalotus produces two kinds of
leaves, a normal, non-carnivorous leaf and a pitcher-shaped pitfall trap. It is seen that the pitcher-shaped leaves of Cephalotus
have evolved independently and are not related to other pitfall traps (like
Sarracenia and Nepenthes). The similarity
is the result of convergent evolution (acquisition of characters
resembling each other in function due to similar environmental
conditions, not due to common ancestry).
Reference: Hasebe (2005), Angiosperm
Phylogeny Group (2003), Hilu et al.
(2003), and others.