Coastal groundsel is the purple exception

Every now and then I throw in a plant from elsewhere that has become established in Australian bushland. A weed, or more specifically, an environmental weed.

For obvious reasons, many will be from regions with a similar climate to ours. The Cape Province of South Africa for example, home to the Purple Groundsel, as species of Senecio. The leaves are hairy and deeply divided, with the margins rolled under, and the flowerheads typically purple.

Senecio, with 1300 or so species, is perhaps the largest genus of flowering plants. That's even after chunks of it has been carved off into other genera to make it more of a 'natural genus' (that is, all species derived from a shared common ancestor). Familiar garden plants have been excised: such as Dusty Miller, Senecio cineraria, which is now Jacobaea maritima.

Of those still called Senecio today (and expect further changes as botanist try to make this genus more 'natural'), some 200 grow naturally in South Africa and nearly 100 in Australia. Among the dozen or so introduced - and weedy - species in Australia is Senecio elegans, the Purple Groundsel.

I saw it most recently in Tasmania, growing in sand at Dennes Point, at the northern tip of Bruny Island. This purple-flowered daisy - although flowers can be sometimes red, pink or white - is a weed of coastal dunes in southern Australia, New Zealand and North America.

It was introduced into Australia as an ornamental but clearly survives well unattended in this sort of coastal habitat. In Tasmania, it is one of four introduced species of Senecio - supplementing the 27 native species - and the only one with purple flowerheads. As in the rest of Australia, I think, all other species have yellow flowerheads.

Technically, it's the ligules or the large 'petal' of the outer flowers in the flowerhead that are purple. The middle of the flowerhead, where the ligule-less disk flowers hang out, is yellow. It seems that all, or at least the vast majority, of weedy Purple Grounsel's are purple-flowered, as the name suggests.

There was an interesting essay from a South African gardener in 1972, describing how they crept out at night to get some seed from white-flowered form of Purple Groundsel from outside the local Magistrate's Court. Most of the offspring did carry through those white flowers (flowerheads), but some flowers emerged crimson and lavender - colours he had not seen in the wild populations. 

These colour variants were retained in seed collected from his own plants, although the white continued to dominate. Three years, magenta flowers emerged. They were not so sturdy or as fertile but over a generation or two they got into the swing of it. 

The author, V.R. Northey, took the seed to Kirstenbosch National Botanical Garden where he was told these were 'varieties as yet unknown to science'. It seems these days we assume such variants are part of natural spectrum for this species but in Australia, at least, purple remains the dominant colour.