Friday, August 14, 2015

Botany picture(s) #211: Macrozamia communis

So, about this cycad I mentioned the other day. When I was a student in Germany, cycads were these really weird plants form the dinosaur age of which you may see one or two in the greenhouses of the botanic gardens. Exotic, rare, spectacular.

Here in Australia, I drive an hour and a half to the east where it gets a bit wetter and milder, and the whole forest floor is covered in them.

But yes, they were more diverse and abundant during the Mesozoic, and they appear to be a bit odd just because there are so few of them left. Essentially they look like a cross between a palm and a conifer: on the one hand they have large, pinnate leaves and fat, un- or rarely branched stems, on the other hand they are gymnosperms, carrying their ovules and thus their seeds freely on the surface of specialised leaves that are generally arranged in cones.

The above is a male cone of Macrozamia communis. I placed it on the dirt road for photographing because there was little light in the understorey.

The individual microsporophylls - the male leaf organs that are homologous to stamens in flowering plants - have large numbers of scattered pollen sacs. A far cry from the regularly four pollen sacs on the familiar, small angiosperm stamens.

I had seen and photographed male cones before, but our little stroke of luck on the recent field trip was to come across a mature female cone so that we could discuss it with the students. The megasporophylls have a long petiole, a spine at the end, and two ovules. Pollination success seems to be extremely high.

I have not observed it myself, but I am being told that these plants are actually insect pollinated. Apparently they warm up their cones in the evening and attract large numbers of beetles that spend the night there.

The outer coat of the seeds is kind of plasticy-spongy and orange-red, indicating that it is probably meant to be eaten to disperse the seeds. However, according to ANU professor Mike Crisp there is no native animal that does eat them; it is possible that the dispersing agent was part of the extinct macrofauna of the continent.

That being said, one of my colleagues mentioned over lunch that feral pigs supposedly eat them. If that is the case, and if the seeds come out undamaged, the plant may have found a new dispersing agent.

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