Friday, 24 December 2010

Weedy teaser



A 'weedy' daisy in eastern Australia known as Cobblers Peg, Pitch-forks or on Lord Howe Island, Teasers, has long been regarded as an introduced species from South America.

Bidens pilosa as it is scientifically named, has usually 3-lobed, hairy leaves, and typical daisy flowers with yellow middle and white ray florets (the bits might call petals – a daisy ‘flower’ is a compound structure of many flowers).

Although it favours disturbed areas and its barbed seeds latch on to any passing animal, one of the scientists at Sydney's Botanic Gardens Trust reckones it may be a local plant taking advantage of a changing environment.

This theory arose from some historical research by plant ecologist Doug Benson. Doug compiled a list of all the plant species collected at Botany Bay in 1770 by Joseph Banks and Daniel Solander, the naturalists who accompanied James Cook on the Endeavour.

Using an unpublished list of specimen material held at the Natural History Museum in London, together with previously unavailable specimens held at the National Herbarium of NSW, there is now a list of 132 plant species collected from Botany Bay between 29 April and 2 May, in 1770.

Among the specimens are many species which still occur in remnant vegetation around Botany Bay. A particularly interesting record is a specimen of Bidens pilosa held in the herbarium.

So circumstantially, it seems likely that this species was here prior to European settlement. It may have arrived and travelled through Australia with earlier migrations or through trading in Northern Australia – it is also found in tropical regions of the world.

It’s interesting to test our definition of a ‘weed’. Put simply, it is a plant out of balance. In this case it may be a native species adapting well to human disturbance. There are certainly other weedy Australian plants, such a few of the wattle species and in some situations sweet pittosporum.

Sorting out the true origins of Bidens pilosa would require DNA sequencing, to compare the genes of the Australian populations with those overseas. We have yet to do this.

Image: A photo of Cobbler's Peg by Terry Tame from our website. You can find out more about this species on Sydney's Botanic Gardens website: see PlantNET or the Botany of Botany Bay site. *This posting is from the Radio Archives (October 2007).

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