Saturday, September 13, 2014

Botany picture #174: Banksia serrata cone

A cone of Banksia serrata (Proteaceae), Australia, 2014. Often, seemingly simple and everyday things can lead to a number of intriguing questions when thought through. In this case, note first that there are very few follicles ("seed pods" - the red, hairy blobs in the picture) developing from what was a spike of dozens if not hundreds of flowers. In other words, most flowers were unsuccessful.

But why? Are these plants suffering from pollinator limitation, that is do they not get enough pollen to fertilise more flowers? Or do they get enough pollen, but most of it is from incompatible individuals? Many plants have incompatibility systems to ensure that they only accept pollen from sufficiently distantly related individuals, to avoid inbreeding. Maybe there just aren't enough compatible sex partners within a realistic distance, perhaps because the local population is genetically impoverished? Then again, maybe the plant could theoretically develop more genetically worthwhile fruits but it only ever "wants" to develop a few per cone because it cannot afford more, resource-wise, and so it aborts the rest. Offspring is expensive, and Proteaceae generally live on very nutrient-deficient soils.

Whatever it is, there is an interesting question here. I assume people will have studied it already, but I just don't know at the moment.

Another one is raised by the dry, dead flowers still attached to the cone. Some Banksias drop the dead flowers, e.g. B. integrifolia, some keep them. The latter state is often interpreted as an adaptation to frequent fire, but I recently heard an ecologist argue that many of the characters traditionally interpreted in that way arose before Australia dried out and became very fire-prone, so they couldn't have been adaptations. Well... don't characters always have to arise randomly before selection can begin to work on them? Where would you draw the line then?

That's the nice thing about the world around us: there is so much to figure out.

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