''Stylidium'' (the triggerplants or trigger plants) is a genus of
dicotyledon
The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, ...
ous
plant
Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...
s that belong to the family
Stylidiaceae. The genus name ''Stylidium'' is derived from the Greek ''στύλος'' or ''stylos'' (column or pillar), which refers to the distinctive reproductive structure that its flowers possess. Pollination is achieved through the use of the sensitive "trigger", which comprises the male and female reproductive organs fused into a
floral column that snaps forward quickly in response to touch, harmlessly covering the insect in pollen. Most of the approximately 300
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
are only found in
Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
, making it the fifth largest genus in that country. Triggerplants are considered to be
protocarnivorous or
carnivorous
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...
because the glandular
trichome
Trichomes (; ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a plant ...
s that cover the
scape and flower can trap, kill, and digest small insects with
protease
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalysis, catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products ...
enzymes produced by the plant. Recent research has raised questions as to the status of protocarnivory within ''Stylidium.''
Characteristics

The majority of the ''Stylidium'' species are
perennial herbs of which some are
geophytes that utilize
bulb
In botany, a bulb is a short underground stem with fleshy leaves or leaf basesBell, A.D. 1997. ''Plant form: an illustrated guide to flowering plant morphology''. Oxford University Press, Oxford, U.K. that function as food storage organs duri ...
s as their storage organ. The remaining small group of species consists of
ephemeral
Ephemerality (from the Greek word , meaning 'lasting only one day') is the concept of things being transitory, existing only briefly. Academically, the term ephemeral constitutionally describes a diverse assortment of things and experiences, fr ...
annuals.
[Good, R. (1925). On the Geographical Distribution of the Stylidiaceae. ''New Phytologist'', 24(4): 225-240.]
Members of the genus are most easily identified by their unique
floral column, in which the
stamen
The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10
Morphology and terminology
A stamen typically consists of a stalk called the filament ...
and
style
Style, or styles may refer to:
Film and television
* ''Style'' (2001 film), a Hindi film starring Sharman Joshi, Riya Sen, Sahil Khan and Shilpi Mudgal
* ''Style'' (2002 film), a Tamil drama film
* ''Style'' (2004 film), a Burmese film
* '' ...
are fused. The column—also commonly called a "trigger" in this genus—typically resides beneath the plane of the flower. ''Stylidium'' flowers are
zygomorphic
Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts.
Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spir ...
, which means they are only symmetrical in one plane.
[Laurent, N., Bremer, B., Bremer, K. (1998). Phylogeny and Generic Interrelationships of the Stylidiaceae (Asterales), with a Possible Extreme Case of Floral Paedomorphosis. ''Systematic Botany'', 23(3): 289-304.] Flowers usually bloom in the late spring in Australia.
[Erickson, Rica. (1961). An introduction to triggerplants. ''Australian Plants'', 1(9): 15-17. (Available online]
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Morphology

Species of the genus ''Stylidium'' represent a very diverse selection of plants. Some are only a few centimeters tall, while others can grow to be tall (''
S. laricifolium''). One typical plant form is a dense
rosette of leaves close to the ground that gives rise to the
floral
Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants (Flowering plant, angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls in ...
spike in the center. Plant forms range from wiry, creeping mats (''
S. scandens'') to the bushy ''S. laricifolium''.
[Darnowski, Douglas W. (2002). ''Triggerplants''. Australia: Rosenberg Publishing. ]
Flower morphology differs in details, but ascribes to a simple blueprint: four petals, zygomorphic in nature, with the trigger protruding from the "throat" of the flower and resting below the plane of the flower petals. Flower size ranges from many species that have small wide flowers to the wide flowers of ''
S. schoenoides''. Flower color can also vary from species to species, but most include some combination of white, cream, yellow, or pink. Flowers are usually arranged in a spike or dense
raceme
A raceme () or racemoid is an unbranched, indeterminate growth, indeterminate type of inflorescence bearing flowers having short floral stalks along the shoots that bear the flowers. The oldest flowers grow close to the base and new flowers are ...
, but there is at least one exception to the rule: ''
S. uniflorum'', as its name suggests, produces a single flower per
inflorescence
In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a mai ...
.
Leaf morphology is also very diverse in this large genus. Some leaves are very thin, almost needle-like (''
S. affine''), while others are short, stubby, and arranged in rosettes (''
S. pulviniforme''). Another group of species, such as ''S. scandens'' (climbing triggerplant) form scrambling, tangled mats typically propped up on
aerial root
Aerial roots are Root, roots growing above the ground. They are often Plant development#Adventitious structures, adventitious, i.e. formed from nonroot tissue. They are found in diverse plant species, including epiphytes such as orchids ('' ...
s.
Pollination mechanism

The column typical of the genus ''Stylidium'' is sensitive and responds to touch. The change in pressure when a pollinating insect lands on a ''Stylidium'' flower causes a physiological change in the column
turgor pressure
Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall.
It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilibri ...
by way of an
action potential
An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...
, sending the column quickly flying toward the insect.
[Findlay, G.P. and Pallaghy, C.K. (1978). Potassium chloride in the motor tissue of ''Stylidium''. ''Australian Journal of Plant Physiology'', 5(2): 219 - 229. (Abstract available online]
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Upon impact, the insect will be covered in pollen and stunned, but not harmed. Because the column comprises the fused male and female reproductive organs of the flower, the stamen and
stigma take turns in dominating the function of the column—the
anther
The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10
Morphology and terminology
A stamen typically consists of a stalk called the filament ...
s develop first and then are pushed aside by the developing stigma. This delayed development of the stigma prevents
self-pollination
Self-pollination is a form of pollination in which pollen arrives at the stigma of a flower (in flowering plants) or at the ovule (in gymnosperms) of the same plant. The term cross-pollination is used for the opposite case, where pollen from ...
and ensures that cross pollination will occur between individuals of a population. Different species have evolved the trigger mechanism in different locations, with some attacking the pollinating insect from above and others from below (a "punch in the gut" to the insect).
[Armbruster, W.S., Edwards, M.E., Debevec, E.M. (1994). Floral Character Displacement Generates Assemblage Structure of Western Australian Triggerplants (Stylidium). ''Ecology'', 75(2): 315-329.]
The response to touch is very quick in ''Stylidium'' species. The column can complete its "attack" on the insect in as little as 15 milliseconds. After firing, the column resets to its original position in anywhere from a few minutes to a half hour, depending on temperature and species-specific qualities. The column is able to fire many times before it no longer responds to stimuli. The response time is highly dependent upon ambient temperature, with lower temperatures relating to slower movement.
[Findlay, G.P. (1978) Movement of the Column of ''Stylidium crassifolium'' as a Function of Temperature. ''Australian Journal of Plant Physiology'', 5(4): 477-484.] ''Stylidium'' species are typically pollinated by small solitary bees and the nectar-feeding bee flies (
Bombyliidae
The Bombyliidae are a family of flies, commonly known as bee flies. Some are colloquially known as bomber flies. Adults generally feed on nectar and pollen, some being important pollinators. Larvae are mostly parasitoids of other insects.
Over ...
).
[Armbruster, W. S., and N. Muchhala. 2009. Associations between floral specialization and species diversity: cause, effect, or correlation? ''Evolutionary Ecology'', 23: 159-179.]
Carnivory

''Stylidium'' species with glandular
trichome
Trichomes (; ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a plant ...
s on their
sepal
A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106
Etymology
The term ''sepalum'' ...
s, leaves, flower parts, or
scapes have been suggested to be
protocarnivorous (or paracarnivorous). The tip of the trichome produces a sticky
mucilage
Mucilage is a thick gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion, with the direction of their movement always opposite to that of the secretion of ...
—a mixture of sugar polymers and water—that is capable of attracting and suffocating small insects.
The ability to trap insects may be a defensive mechanism against damage to flower parts. However, trichomes of ''S. fimbriatum'' have been shown to produce digestive enzymes, specifically
protease
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalysis, catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products ...
s, like other
carnivorous plant
Carnivorous plants are plants that derive some or most of their nutrients from trapping and consuming animals or protozoans, typically insects and other arthropods, and occasionally small mammals and birds. They have adapted to grow in waterlo ...
s. Adding species of ''Stylidium'' to the list of plants that engage in carnivory would significantly increase the total number of known carnivorous plants.
[Darnowski, D.W., Carroll, D.M., Płachno, B., Kabanoff, E., and Cinnamon, E. (2006). Evidence of protocarnivory in triggerplants (''Stylidium'' spp.; Stylidiaceae). ''Plant Biology'', 8(6): 805-812. ]
The insects captured by the glandular trichomes are too small to serve any role in pollination. It is unclear, however, whether these plants evolved the ability to trap and kill insects as an adaptation to low environmental nutrient availability or simply a defensive mechanism against insects damaging flower parts.
There is also a correlation between location of ''Stylidium'' species and proximity of known carnivorous species, like
sundews (''Drosera''),
bladderwort
''Utricularia'', commonly and collectively called the bladderworts, is a genus of carnivorous plants consisting of approximately 233 species (precise counts differ based on classification opinions; a 2001 publication lists 215 species).Salmon, Br ...
s (''Utricularia''), the
Albany pitcher plant (''Cephalotus follicularis''), and the
rainbow plant (''Byblis''). While this alone does not prove that ''Stylidium'' species are themselves carnivorous, the hypothesis is that the association arose because ''Stylidium'' species and the known carnivorous plants obtain scarce nutrients using the same source, namely captured insects. Preliminary proof is given that the trapping mechanisms of two associated plants are the same (the
tentacle
In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...
s of ''Byblis'' and ''Drosera''), though this may be only a coincidence and further research must be done.
Recent research has raised questions as to the status of protocarnivory within ''Stylidium.''
Distribution and habitat

Most ''Stylidium'' species are
endemic
Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...
to Australia. In
Western Australia
Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...
alone, there are more than 150 species, at least 50 of which are in the area immediately around
Perth
Perth () is the list of Australian capital cities, capital city of Western Australia. It is the list of cities in Australia by population, fourth-most-populous city in Australia, with a population of over 2.3 million within Greater Perth . The ...
. There are at least four species of ''Stylidium'' that are not confined to the Australian continent: ''
S. tenellum'' is found in
Myanmar
Myanmar, officially the Republic of the Union of Myanmar; and also referred to as Burma (the official English name until 1989), is a country in northwest Southeast Asia. It is the largest country by area in Mainland Southeast Asia and has ...
,
Melaka
Malacca (), officially the Historic State of Malacca (), is a state in Malaysia located in the southern region of the Malay Peninsula, facing the Strait of Malacca. The state is bordered by Negeri Sembilan to the north and west and Johor to t ...
, and
Tonkin
Tonkin, also spelled Tongkin, Tonquin or Tongking, is an exonym referring to the northern region of Vietnam. During the 17th and 18th centuries, this term referred to the domain '' Đàng Ngoài'' under Trịnh lords' control, including both the ...
; ''
S. kunthii'' in
Bengal
Bengal ( ) is a Historical geography, historical geographical, ethnolinguistic and cultural term referring to a region in the Eastern South Asia, eastern part of the Indian subcontinent at the apex of the Bay of Bengal. The region of Benga ...
and Myanmar; ''
S. uliginosum'' in
Queensland
Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...
,
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, ...
, and the south coast of
China
China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
; and ''
S. alsinoides'' in Queensland and the
Philippines
The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...
. The cladistic group ''Stylidium'' contains more than 230 individual species (more than 300 species exist, but many specimens have not yet been formally described),
[Information from an October 26, 2004 edition of "Talking Plants"](_blank)
, a program of the Botanic Gardens Trust, a division of the New South Wales
New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...
Department of Environment and Conservation making it the fifth largest genus in Australia.
''Stylidium'' habitat includes grassy plains, open
heaths, rocky slopes, sandplains, forests, and the margins of creeks and water holes.
Somes species, such as ''
S. eglandulosum'', can even be found in disturbed areas like near roads and under powerlines. Others (i.e. ''
S. coroniforme'') are sensitive to disturbance and are considered rare because of their extremely specific habitat.
Even though many species of ''Stylidium'' may coexist in the same location, natural hybrids between species have not often been reported. Both natural hybridisation in the field and artificial hybridisation in cultivation are rare.
The first natural hybrid, ''
S. petiolare'' × ''
S. pulchellum'', was reported by
Sherwin Carlquist in 1969 between
Capel and
Boyanup in Western Australia.
[Carlquist, S.J. (1969). Studies in Stylidiaceae: New taxa, field observations, evolutionary tendencies. Aliso, 7: 13-64.]
Botanical history

Discovery and description of new ''Stylidium'' species has been occurring since the late 18th century, the first of which was discovered in
Botany Bay
Botany Bay (Dharawal language, Dharawal: ''Kamay'') is an open oceanic embayment, located in Sydney, New South Wales, Australia, south of the Sydney central business district. Its source is the confluence of the Georges River at Taren Point a ...
in 1770 by
Joseph Banks
Sir Joseph Banks, 1st Baronet, (19 June 1820) was an English Natural history, naturalist, botanist, and patron of the natural sciences.
Banks made his name on the European and American voyages of scientific exploration, 1766 natural-history ...
and
Daniel Solander
Daniel Carlsson Solander or Daniel Charles Solander (19 February 1733 – 13 May 1782) was a Sweden, Swedish naturalist and an Apostles of Linnaeus, apostle of Carl Linnaeus.
Solander was the first university-educated scientist to set foot o ...
during their travels in the Pacific with
James Cook
Captain (Royal Navy), Captain James Cook (7 November 1728 – 14 February 1779) was a British Royal Navy officer, explorer, and cartographer famous for his three voyages of exploration to the Pacific and Southern Oceans, conducted between 176 ...
aboard the ''
Endeavour''.
Seven species were collected by Banks and Solander, some of which were sketched by
Sydney Parkinson
Sydney Parkinson ( 1745 – 26 January 1771) was a Scottish botanical illustrator and natural history artist. He was the first European artist to visit Australia, New Zealand and Tahiti. Parkinson was the first Quaker to visit New Zealand.
...
on board the Endeavour and were later engraved in preparation for publication in
Banks' Florilegium. Later, in the early 19th century, the French
botanist
Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...
Charles François Antoine Morren
Charles François Antoine Morren (3 March 1807 in Ghent – 17 December 1858 in Liège), was a Belgian botanist and horticulturist, and Director of the ''Jardin botanique de l'Université de Liège''. Morren is credited with introducing the term " ...
wrote one of the first descriptions of the triggerplant anatomy, illustrated by many botanical artists including
Ferdinand Bauer. Around the same time, British botanist
Robert Brown Robert Brown may refer to: Robert Brown (born 1965), British Director, Animator and author
Entertainers and artists
* Washboard Sam or Robert Brown (1910–1966), American musician and singer
* Robert W. Brown (1917–2009), American printmaker ...
described (or "authored") several ''Stylidium'' species, including ''
S. adnatum'' and ''
S. repens''. More species began to be described as more botanists explored Australia more thoroughly.
In 1958,
Rica Erickson wrote ''Triggerplants'', describing habitat, distribution, and plant forms (
ephemeral
Ephemerality (from the Greek word , meaning 'lasting only one day') is the concept of things being transitory, existing only briefly. Academically, the term ephemeral constitutionally describes a diverse assortment of things and experiences, fr ...
, creeping, leafy-stemmed,
rosette, tufted, scale-leaved, and tropical). It was Erickson that began placing certain species into these
morphologically-based groups, which may or may not resemble true
taxonomic divergences. It was not until the 1970s and 1980s that research of the trigger
physiology
Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...
was begun in the lab of Dr. Findlay of
Flinders University
Flinders University, established as The Flinders University of South Australia is a public university, public research university based in Adelaide, South Australia, with a footprint extending across a number of locations in South Australia and ...
. Douglas Darnowski added to the growing library of knowledge on ''Stylidium'' when he published his book ''Triggerplants'' in 2002, describing an overview of habitat, plant morphology, carnivory, and research done to date. Following its publication, he co-founded the International Triggerplant Society.
[Darnowski, Douglas W. (2002). The history of triggerplants. International Triggerplant Society. (Archived, available online]
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As of 2002, only 221 ''Stylidium'' species were known.
[Wagstaff, S.J. and Wege, J. (2002). Patterns of diversification in New Zealand Stylidiaceae. '']American Journal of Botany
The ''American Journal of Botany'' is a monthly peer-reviewed scientific journal which covers all aspects of plant biology. It has been published by the Botanical Society of America since 1914. The journal has an impact factor of 3.038, as of 20 ...
'', 89(5): 865-874. (Available online
HTML
o
PDF
versions) There are now
over 300 species, many of which are awaiting formal description.
Cultivation

Most ''Stylidium'' species tend to be hardy species and can be easily cultivated in greenhouses or gardens. They are drought resistant, hardy to cold weather, and the species diversity in this genus gives gardeners a wide variety of choices. Most species that are native to Western Australia will be cold hardy to at least -1 to -2 °C. The few that can be found all over Australia, like ''
S. graminifolium'', will tolerate a wider range of habitat since their native ranges includes a great diversity of
ecoregion
An ecoregion (ecological region) is an ecological and geographic area that exists on multiple different levels, defined by type, quality, and quantity of environmental resources. Ecoregions cover relatively large areas of land or water, and c ...
s. Some species of triggerplants are suitable for cultivation outdoors outside of the Australian continent including most of the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
and as far north as
New York City
New York, often called New York City (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...
or
Seattle
Seattle ( ) is the most populous city in the U.S. state of Washington and in the Pacific Northwest region of North America. With a population of 780,995 in 2024, it is the 18th-most populous city in the United States. The city is the cou ...
in the
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
.
Cultivation from seed may be difficult or easy, depending on the species. The more difficult species to grow include the ones that require a period of dormancy or smoke treatment to simulate a
bushfire
A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a ...
. ''Stylidium'' specimens should be grown in a medium that is kept moist and has a relatively low concentration of nutrients. They appear to be sensitive to disturbance of their root systems. Minimization of such disturbance will likely result in healthier plants.
References
External links
Australian Department of the Environment and Heritage document on the "Wongan Hills Triggerplant (''Stylidium coroniforme'') Interim Recovery Plan 2003-2008".
PDF version
FloraBase(Western Australia's flora database) entry on ''Stylidium''.
* Association of Societies for Growing Australian Plants (ASGAP) information on
' and
'.
*
International Plant Names Index
The International Plant Names Index (IPNI) describes itself as "a database of the names and associated basic bibliographical details of seed plants, ferns and lycophytes." Coverage of plant names is best at the rank of species and genus. It inclu ...
(IPNI
list of published ''Stylidium'' species names
Photos and animationsof triggerplants, featuring several species.
The International Triggerplant Society
{{Taxonbar, from=Q1518289
Asterales genera