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Triggerplant

2007 Schools Wikipedia Selection. Related subjects: Plants

                        iTriggerplants
   Curtis's Botanical Magazine print of Stylidium scandens.
   Curtis's Botanical Magazine print of Stylidium scandens.
                  Scientific classification

   Kingdom:  Plantae
   Division: Magnoliophyta
   Class:    Magnoliopsida
   Order:    Asterales
   Family:   Stylidiaceae
   Genus:    Stylidium
             Sw. ex Willd.

                                   Species

   See separate list.

   Triggerplants (also trigger plants) are a group of dicotyledonous
   plants that belong to the genus Stylidium (family Stylidiaceae). Most
   of the approximately 300 species are only found in Australia, making it
   the fifth largest genus in that country. Pollination is achieved
   through the use of the sensitive "trigger" (male and female
   reproductive organs fused into a floral column) that snaps forward
   quickly in response to touch, harmlessly covering the insect in pollen.
   Triggerplants can also be described as being protocarnivorous because
   the glandular trichomes that are just below the flower can trap and
   kill small insects, but cannot digest them.

Characteristics

   The majority of the triggerplants are perennial herbs of which some are
   geophytes that utilize bulbs as their storage organ. The remaining
   small group of species consists of ephemeral annuals.

   The triggerplants are most easily identified by their unique floral
   column, in which the stamen and style are fused. The column--also
   called a "trigger" in this genus--typically resides beneath the plane
   of the flower. Triggerplant flowers are zygomorphic, which means they
   are only symmetrical in one plane. Flowers of triggerplants usually
   bloom in the late Spring in Australia.

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 1.8 meters tall ( S. laricifolium). The typical plant form is a
   dense rosette of leaves close to the ground that gives rise to the
   floral spike in the centre. Atypical plant forms ranges from wiry,
   creeping mats ( S. scandens) to the bushy S. laricifolium.

   Flower morphology differs in details, but ascribes to a simple
   blueprint: four petals ( S. hispidium has five), zygomorphic in nature,
   with the trigger protuding from the "throat" of the flower and resting
   below the plane of the flower petals. Flower size ranges from many
   species that have small 0.5 cm wide flowers to the 2-3 cm wide flowers
   of S. schoenoides. Flower colour 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, but there is
   at least one exception to the rule: S. uniflorum, as its name suggests,
   produces a single flower per inflorescence.

   Leaf morphology is again 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). One of the unusual
   specimens is S. scandens (Climbing triggerplant) in which the leaves
   have a modified tip in the shape of hook that helps it climb on top of
   surrounding vegetation.

Pollination mechanism

   The column in triggerplants is sensitive and responds to touch. The
   change in pressure when a pollinating insect lands on a triggerplant
   flower causes a physiological change in the column turgor pressure by
   way of an action potential, sending the column quickly flying toward
   the insect. Upon impact, the insect will be covered in pollen and
   stunned, but not harmed. Because the column is essentially the fused
   male and female reproductive organs of the flower, the stamen and
   stigma take turns in dominating the function of the column--the anthers
   develop first and then are pushed aside by the developing stigma. This
   delayed development of the stigma prevents self-pollination 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).

   The response to touch is very quick in triggerplants, completing its
   "attack" on the insect in 15 milliseconds. After firing, the trigger
   resets to its original position in anywhere from a few minutes to a
   half hour, depending on temperature and species-specific qualities. The
   trigger 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.

Carnivory

   Bud and scape of S. fimbriatum displaying the trichomes that can trap
   and kill insects.
   Enlarge
   Bud and scape of S. fimbriatum displaying the trichomes that can trap
   and kill insects.

   Members of the genus are considered to be protocarnivorous (or
   subcarnivorous). They have glandular trichomes projecting from sepals,
   leaves, flower parts, and the scape. The tip of the trichome produces a
   sticky muscilage--a mixture of sugar polymers and water--that is
   capable of attracting and suffocating small insects. Unlike true
   carnivorous species of plants, triggerplants are thought to not produce
   digestive enzymes and must rely on bacteria, fungi, or other
   decomposition processes to release the nutrients stored in the
   muscilage-bound prey, though more research must be done to support that
   hypothesis. The insects captured by the glandular trichomes are much
   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 triggerplant location and proximity
   of known carnivorous species, like sundews (Drosera), bladderworts
   (Utricularia), the Albany pitcher plant (Cephalotus follicularis), and
   the rainbow plant (Byblis). While this alone does not prove that
   triggerplants are themselves carnivorous, the hypothesis is that the
   association arose because triggerplants and the known carnivorous
   plants obtain scarce nutrients using the same source (captured
   insects). Preliminary proof is given that the trapping mechanisms of
   two of the triggerplant-associated plants are the same (the tentacles
   of Byblis and Drosera), though this may be only a coincidence and
   further research must be done.

Distribution and habitat

   Most species of triggerplants are endemic to Australia. In Western
   Australia alone, there are more than 150 species, at least 50 of which
   are in the area immediately around Perth. There are at least four
   species of Stylidium that are not confined to the Australian continent:
   S. tenellum is found in Myanmar, Melaka, and Tonkin; S. kunthii in
   Bengal and Myanmar; S. uliginosum in Queensland, Sri Lanka, and the
   south coast of China; and S. alsinoides in Northeast Australia,
   Queensland, and the Philippines. The cladistic group Stylidium contains
   more than 230 individual species (more than 300 species may exist, but
   many specimens have not yet been formally described), making it the
   fifth largest genus in Australia.

   Triggerplant 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. coronmiforme) are
   sensitive to disturbance and are considered rare because of their
   extremely specific habitat.
   S. violaceum from Ferdinand Bauer's 1813 Illustrationes Florae Novae
   Hollandiae.
   Enlarge
   S. violaceum from Ferdinand Bauer's 1813 Illustrationes Florae Novae
   Hollandiae.

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 in 1770 and described by Joseph Banks and Daniel Solander.
   Later, in the early 19th century, the French botanist Charles Morren
   wrote a monograph on the triggerplant anatomy, illustrated by many
   botanical artists including Ferdinand Bauer. Around the same time,
   British botanist Robert Brown 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, 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 was
   begun in the lab of Dr. Findlay of Flinders University. Douglas
   Darnowski added to the growing library of knowledge on triggerplants
   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 attempted to assist in the
   organization of the International Triggerplant Society, which has not
   been formally created yet.

   As of 2002, only 221 Stylidium species were known. There are now over
   300 species, many of which are awaiting formal description.

Cultivation

   Most triggerplants 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 ecoregions. Some species of triggerplants are
   suitable for cultivation outdoors outside of the Australian continent
   including most of the United Kingdom and as far north as New York City
   or Seattle in the United States.

   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.
   Triggerplants should be grown in a medium that is kept moist and has a
   relatively low concentration of nutrients. It should also be noted that
   triggerplants appear to be sensitive to disturbance of their root
   systems. Minimization of such disturbance will likely result in
   healthier plants.
   Retrieved from " http://en.wikipedia.org/wiki/Triggerplant"
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