Cotula alpina, Aussie invader reaches Assynt
On 31st July 2020, Duncan Donald, BSBI Recorder for West Ross, was visiting the northernmost part of his botanical territory, accompanied by his daughter Flora. The car-park at Inverkirkaig (NC085193) was their starting point for recording along the south side of the river.
No sooner had they got out of their car than Flora noticed a familiar plant on the roadside verge of the car-park (photo 1). It was a substantial patch, with several small outliers, of the tight-knit rosettes of one of the buttonweeds Cotula alpina (photos 1-2). Duncan e-mailed me about it the following day.
Six members of this genus, belonging to the daisy family, and originally hailing from Australia, New Zealand and South Africa, are now naturalised in the British Isles. This particular species is native to south-east Australia, and was first noted in the wild here in the 1970s, having either arrived in wool shoddy or escaped from a garden.
It is now locally abundant on moorland tracks in parts of northern England and along the coast and roadsides on the Coigach peninsula in West Ross, where it was first noted in 2009. Since then it has been recorded from 25 monads (1km squares) in that area, suggesting that it may have been ‘well-established for several decades’. It was only a matter of time before it found its way a little further north to Assynt, and it has now done so.
Cotula alpina is a prostrate perennial with rooting stems, pinnate leaves and short-stalked dull-yellow flowerheads, which are efficient at seed production (photos 3-4). It forms dense patches in closely-grazed grassland, where it can out-compete many native species, even daisies. It is spread by sheep, humans and vehicles and, once established, cannot be controlled without considerable ‘collateral damage’. However, it can be shaded out by taller native vegetation, as happened to a small amount that I translocated, as an experiment, to a gravel-covered ‘alpine bed’ in my garden at Nedd. We shall keep an eye out for its likely spread locally.
Cotula alpina (Asteraceae) naturalised in the British Isles. Walker K.J., Robinson, L. and Donald D., 2020. British and Irish Botany 2(1), 43-45.
Ian M. Evans