New Zealand's 'tumbleweed'

Masses of spinifex seedheads are ripening along the Wanganui coastline, ready to detach themselves and scurry along the beach.

The asterisk-shaped seedheads blow in the wind, carrying seeds of the dune grass to new places. There the lucky ones can be buried by damp windblown sand and produce new plants.

Called kowhangatara, silvery sand grass and hairy, coastal, rolling or beach spinifex, the dune grass Spinifex sericeus is common on the dunes that stretch from Waverley to Paraparaumu. It's also found on the east coast of Australia.

It is low, spreading and perennial, with long runners that cover and colonise bare sand right down to the high tide mark. Its roots and leaves help to quickly bind the sand, and it is said to form lower and gentler dunes than the introduced marram grass.

The species is often planted to stabilise disintegrating sand dunes. It is effective, but very vulnerable to browsing by rabbits, Wanganui ecologist Colin Ogle says.

Coastal spinifex has both male and female plants, which sometimes grow in great masses of the same sex. Male plants produce flowers with windblown pollen. The pollen fertilises the flowers on female plants that produce seed.

The detached seedheads are New Zealand's version of a tumbleweed, though the term "tumbleweed" is usually reserved for steppe and desert plants that have a similar way of spreading their seed around. Many of them detach just above their roots, so that the whole dried plant blows in the wind, shedding seed as it goes.