FLORA

CONSERVING OUR REMARKABLE TRIGGERPLANTS

Juliet Wege

The triggerplant genus Stylidium is rather extraordinary. Famed for its incredible pollination system in which a touch-sensitive column or ‘trigger’ transfers pollen to and from insects, this large and charismatic genus also packs a punch in the beauty stakes. Triggerplant flowers come in a dazzling assortment of colours, shapes and sizes, are variously arranged and orientated, and are often adorned with hairs and small, intricate appendages. Furthermore, their growth forms are often highly ornamental and are remarkably diverse, encompassing rosetted or stoloniferous (running) perennials, dwarf shrubs, climbers, stilt Triggerplants know how to pack a punch – a native bee plants, cushion plants, geophytes (which die back carrying a greenish pollen load gets thumped again by over summer to grow again next year), and tiny Stylidium squamosotuberosum. Photo: Juliet Wege annual herbs. Australia’s remarkable south-west region home to But for all this wonderful variation, triggerplants the greatest diversity. In this region, triggerplants have a dark side — a well-founded reputation as grow in most habitats, and it is common for being taxonomically problematic and difficult to several different species to grow and flower identify; however, this is gradually beginning to together. Unfortunately, the south-west region is change. Over the past 20 years, a range of also where many triggerplants are either poorly scientists have made extraordinary advances in the known or under severe threat in the wild. discovery, collection and description of new species, resulting in a much better understanding Underpinning conservation efforts in the south- of triggerplant diversity in Australia. The genus is west and beyond is a broad-ranging research now known to comprise at least 300 species, most program being conducted at the Western of which are endemic to Australia, with Western Australian Herbarium at the Department of Biodiversity, Conservation and Attractions (DBCA). This program not only includes the documentation of new species, but also the revision of known species and resolution of nitty-gritty nomenclatural issues, the sorting and classification of herbarium specimens, rare flora survey and conservation assessments, the study of evolutionary relationships and, perhaps unsurprisingly, a little pollination research.

Ingenious pollination Triggerplant flowers are highly specialised. The male and female organs of the flower are fused together into a column that is usually bent at the throat of the flower so that it rests against the labellum (the tiny, modified fifth petal). At the tip of the column are the reproductive structures — male anthers and the female stigma, the latter usually developing after the pollen is released from the anthers. When a visiting insect probes for nectar, the column rapidly rotates so the tip hits the insect, either dusting it with pollen or, if the A bee fly pollinates the threatened species Stylidium stigma has developed, retrieving pollen that the applanatum. Photo: Juliet Wege insect may already be carrying.

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Triggerplant pollination has been correct spot on each. The clocked at 15–30 milliseconds, direction of column movement making it one of the fastest plant (whether ventral, lateral or movements known. The rapid dorsal), and the length and firing motion is followed by a shape of the column help to much slower resetting, which dictate the precise part of the returns the column to its original insect’s head, thorax or abdomen position so that it can be that will be hit. The same insect retriggered (within minutes in might visit three different hot conditions). The rapid triggerplants, only to be hit on movement and slow resetting the side of the thorax, the top of are brought about by changes in the head and the tip of the the distribution of potassium abdomen — they simply don’t and chloride ions in the column stand a chance! bend, and associated changes in the shape of specialised motor A collection at the core of cells. conservation efforts Ongoing research at sites across The Stylidium collection at the the South West region is Western Australia Herbarium, revealing that a wide variety of which consists of more than nectar-gathering insects 12,250 preserved specimens, is pollinate triggerplants, including at the centre of the Stylidium an especially large range of large research program and associated and small bee-flies and solitary conservation efforts. Sorting and native bees. All are undeterred accurately cataloguing this by the unique form of collection, which has more than punishment dished out to them; tripled in size in the past 40 they seem to be long-resigned years, has been vital to to their role as pollen couriers, understanding what species repeatedly visiting different occur in Western Australia, flowers in search of sweet nectar, where they grow and how rare and thus the triggerplant they are. This baseline succeeds in moving pollen from information is essential for one plant to the next. Species discovered at the Western conservation management, Australian Herbarium: Stylidium Watching for pollinators takes a especially in view of the diplotrichum (top), S. perula (centre), degree of patience (particularly significant numbers of S. perplexum (bottom). Photos: Juliet in tick-prone habitats), but on a triggerplants that are known to Wege sunny morning it usually doesn’t be rare, threatened or otherwise take long to observe some of conservation concern. to know exactly what you’re looking for—a sound taxonomic trigger action, particularly at sites There are 99 Stylidium taxa listed framework is crucial. where there are lots of plants in on the Threatened and Priority flower. Insects will happily move Flora list for Western Australia, To produce this framework, each between flowers and, after a more than half of which have specimen at the Western short while, a large and often been discovered and named in Australian Herbarium is being colourful pollen load will become the last 20 years. Most need assessed and validated. This visible to the naked eye. In fact, if further survey to better process had led to the correction there is more than one Stylidium document their distribution and of many mis-identifications and species growing in the vicinity, abundance, as well as any threats a suite of new species the insects are likely to move to their survival. Triggerplants discoveries including: Stylidium between them, and more than can be challenging to survey; diplotrichum, a rare and stunning one pollen splodge may become they are often difficult to find large-flowered species from the visible. This is the really when sterile, usually have narrow Lesueur sandplains; S. perula, a ingenious thing about flowering windows, and different sprawling, stoloniferous species triggerplant pollination: different species can be easily confused with a distribution centred on species of Stylidium can place with one another. Not only do the Avon Wheatbelt; and pollen in different places on you need to be in the right place S. perplexum, a lignotuberous different kinds of pollinators and at the right time, but you need shrub from near Dardanup. In can retrieve pollen from the

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asymmetric corolla lobes. This tiny triggerplant is currently known from just three sites and is being threatened by feral pig diggings and inappropriate off- road vehicle use. A team of people will be out and about this year, taking advantage of the good seasonal conditions to survey the known populations and search for more.

What the future brings Stylidium remains in a state of taxonomic flux as our natural history collections continue to be A new population of the conservation-listed species Stylidium tylosum was sorted and classified, new species discovered by chance last year. Photo: Juliet Wege formally described, and the scientific names researched and each case, the taxonomic status conservation status of two taxa validated. A taxonomic account of these species was confirmed from the Avon Wheatbelt of the genus is being prepared by relocating and examining (Stylidium applanatum and and will include web-delivered them in the wild. This is a plant S. coroniforme s u b sp . fact sheets and an interactive group that demands field work, amblyphyllum) being upgraded key, both of which will be full of not only to obtain key data and to Threatened. Two more species photographs and information resolve taxonomic issues, but to will be targeted this year: S. that will revolutionise inform conservation. hygrophilum, from east of identification and facilitate Margaret River, and conservation efforts across the Spring surveys S. asymmetricum, from the country. So watch this space. No, Wandoo National Park. better still, go and watch some Every spring, I integrate field- triggerplants. You’ll be amazed based taxonomic research with Stylidium hygrophilum is one of a at what you see. surveys of poorly known select number of leafless triggerplants: it is a geophyte, triggerplants. This might involve Juliet Wege is a Senior Research a targeted search of a particular having a rhizomatous stem that Scientist at the Western area to look for new populations lies undetected in the soil until of rare species, gathering late spring, at which time its Australian Herbarium. information on pollinators or attractive apricot-pink flowers population numbers, or come into bloom. There are less than 250 individuals known in The hunt is on for more populations of assessing habitat preferences or the tiny triggerplant Stylidium quality. Sometimes it simply the wild, a sobering statistic that asymmetricum. Photo: Juliet Wege means following my instincts and spurred a seed-banking quest in stopping the car to search a site 2014 during a private trip to I’m passing because my Margaret River. I was able to triggerplant radar has begun to convince my long-suffering quiver. Just last year those partner to help me bag plants instincts turned up a new with developing fruit so that population of Stylidium tylosum, seed could subsequently be a pretty but little-known species collected by a DBCA from the southern Avon Conservation Officer and sent to Wheatbelt. Western Australia’s Threatened Flora Seed Centre. This teamwork Targeted surveys for the resulted in around 2,500 seeds triggerplants most at risk are being banked. often done in collaboration with DBCA Conservation officers and The second species to be volunteers, who have fantastic targeted for surveys this year is regional knowledge. Such a S. asymmetricum, an ephemeral collaboration recently led to the herb named for its unusual,

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