Tuesday, 13 December 2016

Same-sex Wedding Bush adds up


The scrub at Cranbourne Gardens has great conservation significance but for much of the year it can seem rather drab - unless you find wallabies, bandicoots and the occasional koala interesting. Which of course we all do.

In sprinter (these pictures were taken in late September, pretty much at the end of the flowering season), one plant seems to shock the bushland into action, being followed by native heath, tea-trees and more cryptic ground orchids. None of them are as floriferous as the Wedding Bush, Ricinocarpos pinifolius. It has a lot of flowers and I'm assuming the Wedding allusion in the common name is because in flower this bush is very white.


Wedding Bush is relatively common in coastal, and near-coastal, areas of Victoria, then northward to about mid-Queensland and southward to Tasmania.The genus Ricinocarpos is a mostly Australian one, with 15 species native to this country and one only found in New Caledonia.

It's in the family Euphorbiaceae, which means that it can look just about like anything and have flower arrangements that are as weird as you want. At least this one has petals and leaves. The leaves are like a pine-needle, hence the species name 'pinifolius'. The flowers look like a daisy, from a distance at least.

Close up you can see the flowers have five, crisp, white flaps - the petals - hiding five triangular green bits that are the sepals, or calyx. Inside, these flowers at least, is a small fountain of male parts, the stamens.


The flowers are either all male or all female, with each cluster typically containing one female flower and three to six male flowers. I didn't see any obviously female flowers in my photos so I'm assuming they have already faded for the season - they usually open in advance of the males, although occasionally there is a second wave of female flowers.

In a study published in 1989, a population of 54 plants were measure for their gender mix. On a scale of 0 (all male flowers) to 1 (all female flowers) the Wedding Bushes were 0 to 0.68, with a mean of 0.16. That is, plants tend to have far more male flowers than female flowers, and sometimes no female flowers at all.

In case you are struggling with the maths, or more likely my clumsy explication, it seems that while a typical cluster of flowers includes one female and 3-6 males, some (to all) clusters may have no females (no plants or clusters are entirely female flowered). Consequently the mean (or middle) ratio of female to male flowers in a plant is not 1:4.5 but 1:6.3... Of course this was one study, on one population, and the authors caution against too much generalisation.
  
To bring it back to specifics, was my plant a very blokey plant or just past its female prime? Dunno. In any case, apparently this variable mix of genders on a plant works, with most flowers setting seed and even all-male plants contributing their genes to the final outcome.

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