Carnivorous Plants

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In: Lambers H ed. A Jewel in the Crown of a Global Biodiversity Hotspot.
Perth: Kwongan Foundation and the Western Australian Naturalists’ Club Inc.
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CARNIVOROUS PLANTS
Adam T. Cross
INTRODUCTION
PLANTS ARE, TRADITIONALLY, PERCEIVED as rather immo-
bile producers that have evolved a suite of complex
strategies to become less appealing to consumption
by animals. These strategies are as diverse as are the
organisms expressing them, reflecting the strong
selection pressure that animal-plant interactions
such as herbivory and granivory have played over
evolutionary time (e.g., Ehrlich & Raven, 1964).
However, one group of plants has instead evolved
a suite of strategies turning the tables on animals to
become the predators in the animal-plant interac-
tion: the carnivorous plants.
Even within the context of the wider South
West Australian Floristic Region (SWAFR), an
area recognised as the global centre of diversity for
carnivorous plants (Clarke et al., 2018), the Yule
Brook region is highly significant. The diversity
of carnivorous plant species in the Yule Brook
region (26 species) is greater than that of the
whole of Europe, for example. It is also significant
in a regional context, harbouring nearly half of all
carnivorous plant species known from the SWAFR
including several rare and threatened taxa, and the
last remaining Swan Coastal Plain populations
of species previously abundant throughout this
region such as Byblis gigantea and Utricularia
menziesii. This chapter highlights the traits required
for a plant to be carnivorous, and celebrates the
exceptional carnivorous heritage of the Yule Brook
regional flora.
CARNIVOROUS PLANTS
More than 800 species of carnivorous plants are
currently known, from more than 10 independent
evolutionary lineages (Ellison & Adamec, 2018).
These species share a number of functional traits
that together create the ‘carnivorous syndrome’
( Juniper et al., 1989; Ellison & Adamec, 2018):
morphological adaptations facilitating the capture
(and usually attraction) of prey in specialised traps;
methods of killing and subsequently digesting the
captured prey; and capacity to absorb nutrients
from digested prey and use these for growth and
development. Carnivory represents an effective
evolutionary strategy allowing plants to compete
for nutrients in systems where nutrients are poorly
available due to various ecological or edaphic
constraints, and as such, the majority of carnivorous
plants are found in mesic-wet and predominantly
nutrient-poor habitats (Brewer & Schlauer, 2018).
Western Australia, and the SWAFR particularly,
is the heartland of carnivorous plant biodiversity.
Carnivorous plants are some 4.5 times more diverse
in Western Australia than would be expected in
the regional flora (Brundrett, 2009), and the state
harbours approximately a quarter of all carnivorous
plant species currently described worldwide
(Clarke et al., 2018). New species continue to be
discovered and described in Western Australia
(e.g., Jobson, 2013; 2018a; Robinson et al., 2018).

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Crucially, over 90% of all carnivorous plants found
in Western Australia are endemic to the state, and
the vast majority of SWAFR species in particular
are local endemics exhibiting range restriction and
high rates of habitat specialisation. This unique
biodiversity is likely a consequence of the extremely
nutrient-impoverished sandy soils, long isolation,
and significant geological and climatic stability
characteristic of the SWAFR (Hopper & Gioia,
2004; Lambers et al., 2014).
FIGURE 1. Byblis gigantea, an increasingly threatened species once common in seasonally-wet areas in the Yule Brook region. a. A flowering individual
growing amongst low scrub on a seasonally-wet claypan. b. The large cerise-lilac flower of Byblis gigantea. c. Setocoris bybliphilus, a potentially
mutualistic hemipteran bug associated with Byblis gigantea. Photos a-b: Richard Nunn, c: Andreas Fleischmann.
a
bc

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Carnivorous Plants
BYBLIS, THE RAINBOW PLANTS
Byblis (Byblidaceae) is a genus of eight predominantly
Australian-endemic species of annual or short-lived
perennial carnivorous herbs or subshrubs (Cross et
al., 2018c). Byblis species are rather showy plants,
possessing long, glandular linear leaves up to 25 cm
in length and large cerise-lilac flowers in late spring
(Fig. 1). These flowers are buzz-pollinated by native
bees and hoverflies, and are thought to mimic the
flowers of sympatric Thysanotus (Asparagaceae)
species. Prey capture by Byblis is achieved by the
production of sticky mucilage by the small glandular
leaf hairs, and although this mucilage is relatively
weakly-adhesive, all species are highly effective at
trapping small- to medium-sized flying insects
(Cross et al., 2018c). The glands on the leaves of Byblis
are both digestive and absorptive, with phosphatase
production demonstrated and evidence of nitrogen
(N) and phosphorus (P) assimilated from prey into
leaf tissues (Płachno et al., 2006; Cross et al., 2018c).
Additionally, Byblis have a potentially mutualistic
association with predatory hemipteran bugs of the
genus Setocoris (Cross et al., 2018c). These bugs live
on Byblis and feed upon prey captured by the plant
(Fig. 1), potentially assisting in nutrient uptake
and turnover by defecating metabolised nutrients
onto the leaves that are more readily absorbed
(Conran et al., 2002; Lowrie, 2014; Cross et al.,
2018c). Fire appears to be an integral component
to the population dynamics and reproductive
ecology of Byblis, with all eight species exhibiting
a significant germination response or widespread
recruitment from seed in response to exposure to
the germination-stimulating chemicals present in
smoke (Cross et al., 2013; 2018a; 2018b).
Of the eight Byblis species, only the two
perennial species Byblis gigantea and Byblis lamellata
occur outside of tropical northern Australia
(Lowrie, 2014). Although these two species are
closely related, the former is restricted to deep sands
in heathlands on the Geraldton Sandplains north of
Perth, while Byblis gigantea occurs only in seasonally-
wet Leptospermum/Restionaceae scrubland on the
Swan Coastal Plain and Jarrah Forest (Speck &
Baird, 1984; Conran et al., 2002; Cross et al., 2013,
2018c). Setocoris bybliphilus is associated with Byblis
gigantea (Fig. 1). Although Byblis gigantea was
once widespread throughout low-lying areas of the
Canning Basin, it has experienced a rapid decline
in the last century, due primarily to land clearing
and alteration to natural hydrological regimes which
have almost completely eradicated this habitat on
the Swan Coastal Plain (Conran et al., 2002; Cross
et al., 2013; Clarke et al., 2018). The species is now
restricted to only four disjunct remnant populations,
and the Yule Brook region represents the last
remaining habitat for Byblis gigantea on the Swan
Coastal Plain.
DROSERA, THE SUNDEWS
Drosera (Droseraceae) represents the largest
carnivorous plant genus, with approximately 250
species (Fleischmann et al., 2018). The genus is
pan-globally distributed, with species occurring on
every continent, except Antarctica, but the greatest
diversity is found in Australia (165 species, 93%
of which are endemic; Lowrie, 2014). Indeed,
southwest Australia represents the global centre
of diversity for the genus, harbouring at least 113
species of which 96% are endemic (Lowrie, 2014;
Fleischmann et al., 2018). Drosera species are well-
represented in the flora of the Yule Brook region,
with at least 20 species known from the area,
including representatives from Drosera subsections
Bryastrum (the pygmy sundews; Fig. 2), Coelophylla
(Drosera glanduligera; Fig. 3) and Ergaleium (the
tuberous sundews; Figs 4 and 5). The majority
of Drosera species in the Yule Brook region occur
in low-lying, seasonally-wet areas (e.g., Drosera
bulbigena, Drosera heterophylla, Drosera indumenta,
Drosera leucoblasta, Drosera micrantha, Drosera neesii,
Drosera nitidula, Drosera occidentalis, Drosera rosulata
and Drosera tubaestylis) or seasonally-flooded
habitats (Drosera gigantea, Drosera ramellosa) and
drainage lines on sand overlying heavy clays. The
remainder occur among low heathland or shrubland
on deeper sandplains and raised sand dunes (e.g.,
Drosera bulbosa, Drosera drummondii, Drosera
erythrorhiza, Drosera macrantha, Drosera menziesii,
Drosera stolonifera and Drosera zonaria).
Drosera exhibit remarkable diversity in form
and function, with life history ranging from annual
therophytes to perennial tuberous species and life
forms ranging from the minute rosetted Drosera
nitidula (10–15 mm in diameter; Lowrie, 2014) to

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the large, almost bushy Drosera gigantea (30–100 cm
tall; Lowrie, 2014). The leaves of all Drosera species
are covered by glandular emergences (‘tentacles’) on
the adaxial surface which secrete a clear and highly
viscous water-based muco-polysaccharide to trap
prey (Matušikova et al., 2018). Both the lamina
and glandular emergences of many species are
capable of quite remarkable movements ensuring
that this mucilage achieves maximum contact with
captured prey (Fleischmann et al., 2018). Most
notable are the ‘catapult tentacles’ of the annual
species Drosera glanduligera (Fig. 3) and some
species of pygmy Drosera (Poppinga et al., 2012,
2013a; 2013b; Fleischmann et al., 2018). These
tentacles are touch-sensitive, with a hinged zone
at the base, and are capable of lifting and throwing
insect prey into the centre of the concave glandular
lamina in approximately 65 milliseconds (Poppinga
et al., 2012).
UTRICULARIA, THE BLADDERWORTS
Fifteen species of Utricularia (Lentibulariaceae) are
known from the SWAFR, 11 of which occur in the
SWAFR and five of which (Utricularia inaequalis,
Utricularia menziesii, Utricularia multif ida,
Utricularia tenella and Utricularia violaceae) are
recorded from the Yule Brook region (Fig. 6).
Utricularia is a pan-globally distributed genus
with over 230 species, which exhibit remarkable
morphological and ecological variation ( Jobson
et al., 2018b). While most species are terrestrial,
subaquatic or aquatic (either rooted by modified
stems or rootless and floating), a number are highly
specialised epiphytes, lithophytes or rheophytes
( Jobson et al., 2018b). All Utricularia species possess
uniquely modified stems that form hollow bladder
traps. Fluid within these traps is actively pumped
out to create a pressure differential between the
internal and external of the trap, and prey are
sucked in through the narrow trap entrance upon
excitement of fine trigger hairs or upon spontaneous
firing (Sydenham & Findlay, 1973; 1975; Juniper et
al., 1989; Jobson et al., 2018b).
In addition to their remarkable prey-trapping
mechanism, Utricularia exhibit a noteworthy
diversity in floral morphology and pollination
biology ( Jobson et al., 2018b). Flower size, shape and
colour vary widely throughout the genus (Lowrie,
2014; Jobson et al., 2018b), with specialisations
including highly-modified corolla lobes (e.g.,
cd
efh
g
ab
FIGURE 2. Representatives of Drosera subsection Bryastrum (pygmy sundews) occurring in the Yule Brook region. a. Drosera leucoblasta. b. Drosera
micrantha. c. Drosera nitidula. d. Drosera occidentalis. e. Flower of Drosera leucoblasta. f. Flower of Drosera micrantha. g. Flower of Drosera nitidula.
h. Flower of Drosera occidentalis. Photos: Richard Nunn, except f: Thilo Krüger.

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Carnivorous Plants
Płachno et al., 2016) and ultraviolet patterning
(e.g., Gloßner, 1992). Pollinators range from insects
to hummingbirds (Taylor, 1989; Jobson et al.,
2018b), and a noteworthy example of pollinator
specialisation in Utricularia is the SWAFR-endemic
Utricularia menziesii. This species produces the
largest spur in the genus (Płachno et al., 2019)., and
is thought to be pollinated by the Western spinebill,
a small honeyeater (Keighery, 1982; Hopper, 2003),
which pollinates sympatric nectiferous species such
as Grevillea (Proteaceae). Although Utricularia
menziesii is widespread in seasonally wet areas of
a
b
FIGURE 3. The annual species Drosera glanduligera. a. Rosetted growth habit. b. Detail of the ‘catapult’ tentacles. c. Numerous springtails (Collembola)
in the centre of a Drosera. glanduligera leaf captured by the ‘catapult’ tentacles. Photos a: Richard Nunn, b: Andreas Fleischmann, c: Hongtao Zhong.
c

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A Jewel in the Crown of a Global Biodiversity Hotspot
bcd
efh
g
a
FIGURE 4. Erect and scrambling Drosera species occurring in the Yule Brook region. (a) Drosera bulbigena. (b) Drosera drummondii. (c). Drosera
gigantea. (d) Drosera heterophylla. (e) Drosera indumenta. (f) Drosera macrantha. (g) Drosera menziesii. (h) Drosera neesii. Photos: Richard Nunn.
bc
defg
a
FIGURE 5. Rosetted and fan-leafed Drosera species occurring in the Yule Brook region. (a) Drosera bulbosa. (b) Drosera erythrorhiza. (c) Drosera
bulbigena. (d) Drosera ramellosa. (e) Drosera rosulata. (f) Drosera tubaestylis. (g) Drosera zonaria. Photos: Richard Nunn.

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Carnivorous Plants
b
cd
e
f
a
FIGURE 6. UTRICULARIA species occurring in the Yule Brook region. (a) Utricularia inaequalis. (b) Utricularia multifida. (c) Utricularia tenella. (d)
Utricularia violaceae. (e) The bird-pollinated Utricularia menziesii. (f) The subterranean traps and modified stems of Utricularia multifida. Photos a-e:
Richard Nunn, f: Andreas Fleischmann.

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southern southwestern Australia, the Yule Brook
region represents the only remaining population of
this species on the Swan Coastal Plain.
PERSPECTIVES
The Yule Brook region is the most significant
area of remnant natural vegetation in the Perth
metropolitan region for carnivorous plant
biodiversity and conservation. It harbours nearly
half of the known SWAFR carnivorous plant
species, and represents a refuge for several rare and
increasingly threatened taxa. Indeed, the region
represents the last remaining Swan Coastal Plain
populations for several species previously abundant
throughout this region such as Byblis gigantea
and Utricularia menziesii. Crucially, almost all
carnivorous plant species native to the region are
mesic and reliant upon seasonally-wet habitats. The
continued persistence of these species, particularly
in terms of reproductive success and population
regeneration, is intrinsically tied to the maintenance
of natural ecological processes. Most significantly,
these processes include fire and hydrology, and
studies have implicated alteration to natural fire
cycles and hydrological regimes as key threatening
processes for numerous carnivorous plant species
throughout the Swan Coastal Plain (e.g., Jennings &
Rohr, 2011; Cross et al., 2013; 2018c; Lowrie, 2014;
Clarke et al., 2018). As development throughout the
Yule Brook region has already significantly impacted
upon natural hydrological processes resulting in the
loss of numerous populations of Byblis gigantea, for
example (Cross et al., 2013; Lowrie, 2014), failure
to consider the impacts of future developments
on catchments and groundwater movement likely
represents a significant extinction risk for the
region’s carnivorous flora.
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