Monday, January 13, 2014

Fairley & Moore's Native Plants of the Sydney Region

During our recent trip to the Blue Mountains I made some use of Fairley & Moore, Native Plants of the Sydney Region. The positive aspects first: It is most helpful for quickly identifying plant species, at least if you already have a bit of an idea of where to start looking, and allowed us to easily figure out what Grevillea or Persoonia we had just run into. I appreciate very much that the plant groups are arranged in a systematic fashion instead of alphabetically as in some other guides I could mention.

More generally speaking, although I need more sophisticated keys for my actual work I love field guides like these, especially of areas I have never had the chance to visit. At home we have, for example, a guide to the Fynbos flora that was kindly brought back from a visit to South Africa by a postdoc during my time in Switzerland and a guide to the flora of Kazakhstan that was a present from a PhD student in Germany. I cannot actually read the latter except for the Latin plant names but I still enjoy having it.

Using the Sydney Region one really for the first time now, however, it occurs to me that this particular specimen of the genre has a few problems from a scientific perspective. For all the following points, note that what I have is the 'revised third edition published in 2010' so it is not as if the book has the excuse of being terribly old.

First, there are a few cases of outdated nomenclature in the groups that I know my way around. This alone is not too terrible a problem, especially because some of the changes I noticed were made only two years before publication and thus may not have filtered through to the authors.

EDIT: But oh, I forgot, there is also the tendency of the authors to comment "genus X is sometimes treated as part of family Y", which patently means "all available evidence shows that X is part of Y but we like the wrong, outdated classification better." So it is not in all cases merely an oversight.

What is stranger is that the systematics of some of the major groups are seriously outdated. The worst example is perhaps this:
Fork ferns - only two small genera, Psilotum and Tmesipteris, survive as descendants of a group of land plants which was abundant during the Devonian and Silurian periods, 360-440 million years ago, possibly the earliest and most primitive of the vascular plants. They lack true roots and leaves, the functions of these being performed by the stems which provide photosynthesis in the upper part and anchor the plant and absorb water in the lower.
There are actually two distinct ways in which this is plain wrong. For one it has been known for quite some time now that the fork ferns are not living fossils from the Silurian but basically just another group of eusporangiate Monilophytes, like horsetails or Marattiales. In other words, they are ferns that have secondarily lost their roots and reduced their leaves (and Tmesipteris actually has well developed leaves). I lectured on those facts in 2010 and am fairly sure that the information had been available for years at that time.

But if you think about it, sentences like the above are even more misleading. Even if the fork ferns were descendants of 'the earliest and most primitive of the vascular plants' that would not be anything special. Do you know who else is a descendant of the same group? Well, all other living vascular plants, they merely have changed more in the intervening time.

This is an important point that people who aren't trained in phylogenetic thinking tend to miss: An ancestral group (e.g. the early land plants) has not survived as the ancestral group today (e.g. fork ferns, if that were the case) while all the other descendants (e.g. seed plants) were specially created. The term descendant kind of shows that the ancestral group has survived as all of its descendants: all the vascular plants today are some of the early vascular plants of the Silurian after some diversification happened to them.

Something very similar is found in many other chapters: the ancestry of ferns is said to stretch back nearly 350 million years, and the cycads are an 'ancient group'. But of course the same is true for every other group of organisms on the planet.

There is, by the way, an interesting parallel in how similar illogic is applied to human lineages. Whenever I hear somebody saying how old this or that family of nobles or royalty is I cannot help thinking: all human families must by necessity be exactly equally old, the peasants just didn't write their lineages down.

You may already have noticed the word 'primitive' in the quotation above, and that is the final problem with the book. Scala naturae thinking is front and centre for the authors. Fork ferns are primitive; club mosses are 'still showing many primitive characters' although they are already 'more highly developed than the fork ferns'. Throughout, 'those exhibiting features considered by botanists to be primitive are presented ahead of those considered to be advanced'.

I will admit that a slightly teleological interpretation of land plant evolution is perhaps more justified that in most other cases (more on that perhaps another post) but generally language like that is today considered to be bad science. One should be careful with thinking in terms of evolutionary progress; what mostly appears to happen is diversification and random walk - or would you consider duckweed to be more 'advanced' than Selaginella?

In summary, the book is beautifully designed and very useful. But it would be nice if a future fourth revised edition would try to be a bit less misleading about land plant evolution.

No comments:

Post a Comment