Tricky triggerplant taxonomy in The (Tasmanian) Gardens

I first thought that reports of the Broadleaf Triggerplant, Stylidium dilatatum, living in Victoria were, to use the Oscar Wilde line, exaggerated. In their 2009 paper on a new subspecies of Stylidium armeria, Neville Walsh and colleagues dismiss all references to Stylidium dilatatum in Victoria.

That's despite a Tasmanian focused review of the genus in 2001, which included a few collections from Victoria for this predominantly Tasmanian based species. Those records were considered misidentified Stylidium armeria in the 2009 paper.

Turns out this was all but a prelude to the realisation - at least tentatively - that these two names apply to the same species. In 2017, Western Australian Triggerplant guru, Juliet Wege, followed Flora of Tasmania Online in combining the two species and using the older name, Stylidium armeria.  

That seems to be where things sit today and although all authors call for further resolution of the Stylidium graminifolium and its close associates such as the Broadleaf Triggerplant.

When I was travelling through the Bay of Fires area of north-eastern Tasmania last year, I saw the Broadleaf Triggerplant mentioned on a sign honoring the role of Lady Jane Franklin in conserving the conservation area called 'The Gardens', a heathland apparently resplendent in this particular species of trigger plant at the time when she and Sir John Franklin rode their horses through here in the early nineteenth century.

On our visit in early November, there were enough in flower to pique my interest, so I took all these photographs to remind me to check if they had the species name - Stylidium dilatatum - correct on the sign. Turns out they didn't, but the common name still works well.

Broadleaf Triggerplant is generally more robust that the better-known Grass Triggerplant, Stylidium graminifolium, with broader leaves but similar coloured, and triggered, flowers. As to how Stylidium dilatatum purportedly differed from Stylidium armeria, that early paper on the Tasmanian species used leaf shape, and the arrangement of flowers and stomata - stomata being the valves on the leaf surface to allow gas to get in and out of the leaf. 

Most simply, the leaves of Stylidium armeria were said to be slightly broader ('spathulate') at the base than those of Stylidium dilatatum. I gather this wasn't very helpful. 

Easier to distinguish, by the way, is the Small Triggerplant, the white-flowered Stylidium despectum, which also grows in 'The Gardens' heathland. Although that wasn't in flower when I visited, it was mentioned on the sign, with its still current name. 

I should also note that the handful of Triggerplant species in Victoria and Tasmania pale into insignificance against the 150 or so Western Australia but that's often the case.