Sunday, 2 September 2012

Cycads and more botanical revolutions I've missed...

Lake Natron Cycad, near Loliondo. Cycads look rather
palm-like, but are not true flowing plants at all.
Back in April I headed to Loliondo for a few days with a bunch of guides from Thompson Safaris. Along the long and bumpy route I was really pleased to spot some Cycads and jumped out to take a few photos. Spotted in action, I was forced to explain why I was taking pictures of some random tree. My answer at the time was based mainly on the evolutionary history of plants that I'd been taught at school and then probably on into university: Cycads form a remarkably early split from the branching evolutionary tree of seed-bearing plants, their ancestors somehow linking ferns to the much more modern flowering plants.  I was also keen to see this particular species (according to the IUCN commonly known as the Lake Natron Cycad) because it's one more of those remarkably restricted range species that fascinate me.

Now I have a confession to make - once again I was completely wrong!
It seems that there's been another revolution in the world of botany that I'd completely missed and the latest evidence suggests that the group of plants we call gymnosperms (which includes the Cycads, as well as other more familiar groups like the conifers) are not really steps on the way from the 'lower' plants like ferns to the flowering plants, but rather a whole side-branch in evolutionary history. I've spent a while trying to put the full story together, and my conclusion from all the various papers I've been reading, is that it's not yet clear exactly how the new tree of plant life fits together, but it is pretty certain that most of the gymnosperms form a separate group to the flowering plants, and that as a group they were the dominant vegetation at around the time land vertebrates first evolved and right up to form the forests roamed by dinosaurs. They then went through some major extinction events apparently caused by climate change, so that today this once dominant group of plants is far rarer across most of the world than the much newer flowering plants.

So, whilst cycads aren't any longer considered some sort of botanical 'missing link', they are still a very interesting relic of a past landscape. And my reading discovered a few more fascinating things too. A few of the interesting things to remember - all Cycads come as either male or female plants and, obviously, only the females have the big cones that hold the seeds in this group. Those seeds, attractive as they may look, aren't all that good for you - in fact they are really rather toxic even after extensive preparation, and are blamed for a range of brain diseases in human cultures that eat them, such as in Guam. The leads are also rather toxic (full of cyanide in fact), but there's something odd going on with one of the other Tanzanian species that is common on the coast, where the Zanzibar Red Colobus seem to be very keen on eating the leaves apparently without ill effects. And the other thing that interested me is that most (possibly all?) Cycads have an association with nitrogen-fixing bacteria, just like the legumes. That's of interest to me because the habitat the Tanzanian species are found in are usually very low nutrient systems and I wonder if there's possibilities Cycads have some similar roles in their habitats to that of Acacia in the savannas.

All in all there's plenty of interesting things to say about Cycads, and I'm pleased to have found this rather rare species. I was also rather concerned to hear from several people that there's been a massive recent export of these plants to gardens around Tanzania, by people who headed to Loliondo to visit Babu. There certainly didn't seem to be many plants around in the few suitable spots I looked in, and as it's already considered Near Threatened, my guess is that this is, sadly, yet one more species on it's way up the endangered status.

Main reference:
ResearchBlogging.orgM.J.M. Christenhusz, J.L. Reveal, A. Farjon, M.F. Gardner, R.R. Mill & M.W. Chase (2011). A new classification and linear sequence of extant gymnosperms Phylotaxa, 19, 55-70

No comments:

Post a Comment