Tuesday 18 March 2008

Banksias R Us

Of the 76 species of Banksia, 60 occur in SW Western Australia. Although the Stirling Range is the centre of the universe for this iconic genus (20 spp), the Gairdner Range near Geraldton isn't far behind (17 spp). Both regions have endemics.

The Burma Road banksia (Banksia scabrella) is confined to sandy heathlands in the Walkaway – Mingenew and Mt Adams – Arrowsmith River regions near Geraldton. It is considered rare but not currently under threat of extinction. Although they normally flower from September to January, this cultivated specimen was still going strong only last week. The bees were taking advantage of the lengthy flowering period. So were the honeyeaters.

Banksias are pollinated by animals. Their inflorescences are made up of hundreds — sometimes thousands — of small, elongate flowers filled with nectar. In the Burma Road banksia, the flowers open from the top of the inflorescence. (In most species, they open from the bottom.)

Just before that takes place, pollen is transferred from the anthers to the stigma. Despite that, the flowers usually don't pollinate themselves. The stigma is not yet receptive and doesn't become so until that pollen is removed — hopefully by a nectar-feeding bird, insect or mammal. Once that occurs, things start moving. The stigma is now ready to receive the other pollen that's shuttled around by the nectar-feeders as they move from flower to flower and plant to plant.

Although there may be huge numbers of flowers on an inflorescence, only a relatively few seeds are produced during a season. They develop inside valved cases embedded in a woody 'cone'. I didn't see any on the Burma Road banksia. I'd love to know if they're as big and bad as this one.

(Note for non-Australians: the big bad banksia men were the villains of May Gibbs' tales of Snugglepot and Cuddlepie, the gumnut babies. I don't think I'm the only one who was on the side of the banksia men.)