The first time we saw this plant growing in the wild was by the River Tweed near Melrose in the Scottish Borders. It is native of Australia and New Zealand. I received an email shortly afterwards to suggest it could be a survivor from the raw wool imported to Galashiels woollen mills in the second half of the 19th century. Wool was often purchased from Australia, and with the wool came foreign seeds; thus the banks of the Tweed became enriched with alien plants.
A. novae-zelandiae in Tasmania. Globose seed-heads 6–10 mm in diameter produced on terminal shoots. Each develops 70-100 achenes. Photo: John Grace.
At that time, a young woman, Ida Hayward, was living at her uncle’s woollen mill in Galashiels and he encouraged her to take an interest in the strange plants. Helped by the eminent English botanist George Claridge Druce she was able to identify the species and together they published a book The Adventive Flora of Tweedside. In the book, the plants are rather crudely illustrated by silhouettes, and some names have changed, but what we call Acaena is there1.
A. novae-zelandiae flowering in Tasmania, showing the white anthers. The flowering is protogynous but the sequential maturation within the flowering head means that ‘selfing’ can occur. Photo: John Grace.
In the last few weeks I’ve been in Australia where Acaena has shown up many times. It is found on rough ground, especially around car parks and also on dampish grassland. My attempts to photograph it close-up have required me to sprawl on the ground, and I have been plagued by the achenes which have tiny hooks. Extricating them from clothing has been ‘family fun’.
More details on habitat in Australia and Britain are found in the review by Gynn & Richards (1985).
The achenes have tiny hooks carried on long stalks and they attach to clothing (like Velcro). Here they have attached to my boot. Photo: John Grace.
It is easy to see how the seeds could become entangled in wool and then exported. There are still many sheep in SE Australia where the plant has its ‘headquarters’. Australian pastoralists in New South Wales and Tasmania became wealthy in the period 1840-1880, aided by the free labour provided by convicts sent from Britain and Ireland. Wool was also imported from New Zealand, but in that country much of the wool was processed to make fabrics and garments in their own mills.
What do we know about the biology of this plant? It was first described by Thomas Kirk in New Zealand. He may not have known that it grew in Australia as well, hence he gave it the patriotic specific name novae-zelandiae. It belongs to the rose family Rosaceae, although this is not immediately obvious. Its globose flowering head consists of many small flowers with no petals, carried aloft on a pubescent stalk that is 5–10 cm long. Its leaves are divided and resemble those of the silverweed and salad burnet (these two are also in the Rosaceae). It is wind pollinated. After pollination the stalk elongates (up to 20 cm) and the green clusters of achenes turn red then brown.
A. novae-zelandiae growing with debris just above the high-tide mark on a sandy beach near Adventure Bay, Bruny Island, Tasmania. The stolons are growing towards the sea. Photo: John Grace.
It spreads by stolons. The image above shows how this works. By this vegetative method it spreads rapidly once a ‘founder’ plant has matured. Sometimes it is advertised by traders as ‘good ground cover’ and a substitute for a grass lawn. Yes, it is pretty, but once you have it you will find it hard to eradicate. As a ‘lawn’? This is surely madness.
As for habitat, I have seen it in locations where holiday-makers visit, and especially in Tasmanian car parks. It flourishes at the edge of the car park on the summit of Mount Wellington, a World Heritage Site. The summit is at 1,271 metres and is covered with alpine scrub with a tundra climate.
Here the plant flourishes in front of a fencepost at the edge of the main car park for the summit of Mount Wellington, Hobart, Tasmania. Flowering heads and leaves are smaller than elsewhere. Photo: John Grace.
The maps below show its distribution. The native range is New Guinea, SE. Queensland to SE. & SW. Australia, New Zealand. In Britain it is most abundant in north-east England and especially on Holy Island (Lindisfarne) where it is considered as a serious invasive.
Distribution of A. novae-zelandiae. In Britain it is spreading. Left: data from BSBI, right: data from GBIF.
How did it get to Lindisfarne? According to Gynn & Richards (1985):
“The first record of A. novae-zelandiae in the area was of a firmly established colony on the banks of the Tweed below Leaderfoot, Roxburghshire, in 1911 …. It has also colonized the banks of the Tweed at Melrose and at intervals from Galashiels to Dryburgh (Hayward & Druce 1919). It is possible that the Lindisfarne populations arose from seeds washed down the Tweed in flood water and across to the island. A more likely explanation is that it was accidentally introduced by people or their dogs, possibly after they had visited Melrose Abbey. Introduction from fruits adhering to birds is also a possibility”.
Long distance dispersal by birds is known from Australia: in particular by ground-nesting petrels and albatrosses (Gynn & Richards, 1985). Human dispersal on socks or trousers has been shown to be formidable (Pickering et al 2011)
The genus name Acaena comes from the Greek ‘akanthos’ meaning thorn. Names given to A. novae-zelandiae in Australia include: biddy biddy, red bidibid, bidgee widgee, buzzy and pirri-pirri bur.
Note
1In the Adventive Flora the plant is called Acaena anserinifolia. In Stace’s New Flora of the British Isles this name is used for a closely related species with bronzy-tinged matt foliage. The two species are easily confused, and so distribution maps may be misleading.
References
Gynn EG & Richards A.J (1985). Biological Flora of the British Isles. No. 161. Acaena novae-zelandiae T. Kirk. Journal of Ecology 73, 1055–1063 doi:10.2307/2260167
Hayward IM & Druce GC (1919). The Adventive Flora of Tweedside. Buncle, Arbroath.
Pickering CM, Mount A, Wichmann MC & Bullock JM (2011). Estimating human-mediated dispersal of seeds within an Australian protected area. Biological Invasions 13, 1869–1880.
©John Grace
Botany in Scotland 