Friday, 2 October 2015

I feel a need to mutter about taxonomy

I had been contemplating a post about taxonomy for some time.  Then I received an email message about orchids which included:
"Don't get too hung up with the scientific names which seem to be in a constant state of change. Petalochilus is back to being Caladenia." 
One issue is how does one know this change has taken place?   Rumours have been around for some time that one of the authors of the last major change - adopted in the ACT at least - had changed his mind, but the Council of Heads of Australian Herbaria (CHAH) had been unable to agree on either the correctness of the previous change or the backstepping.  I posted a somewhat terse view on this.

A number of people have spoken to me, agreeing that the current state of affairs is rather woeful.  I also got a blog-comment from my friend Ian Fraser commenting (inter alia) that
"It's not as if the distinctions between genera and subgenera are facts of nature - such things are ultimately human conceits."
I have replied to Ian's comment setting out my view that taxonomy is more theocratic than democratic, and as a result a view expressed by an Eminence tends to be treated as gospel (or more likely a papal bull, with an emphasis on the bull) , but
1.     With, in most cases, no public recognition that the possible set of taxonomic relationships contains many different views, of which the author has selected one; and 
2.    particularly in the case of orchids, no attempt seems to be made to come to agreement on why one outcome is better than another (except a vague sort of suggestion that the newer one has used more expensive toys so must be better).
The trouble is that for us lay-persons to contribute to science we need consistent labels and there are effectively two choices: the scientific names and the vernacular names.  The latter are far more stable (no-one's career relies on publishing a new arrangement of 'peas' or "daisies') but much more variable and (possibly) less well structured.  I have received another email imploring me not to use vernacular names: it concluded
"I don't mind which group of names you use, but you disrespect your readership by reverting to Tall Greenhoods. We deserve better than that, from you."

I don't want to upset the author of that plea, so will keep an openish mind for the time being.  I do note that in the Plantnet listing - which follows the "traditional" approach - for the genus Caladenia there are 2 species with the common name “Pink fairy” and 3 species with a common name of simply ‘Spider orchid’.

For the ACT the Field Guide to the Orchids follows the views of David Jones.  That is what we use in the field (duhhhh) and it seems to have considerable logic behind it, so that is what I am going to continue to follow.

Much of my issues with the current state of affairs is attributable to the difficulty of finding out any information, in something resembling English, about what goes on with the currently core techniques of DNA sequencing and genome analysis.  With a Masters Degree in Ag Science and 30 years working with some pretty good quality maths-stats guys I can handle some technical stuff.  However I have found it impossible to get the equivalent of "DNA Sequencing for Dummies".  Most descriptions are in such jargon, the process might as well be a chili cook-off.

A significant exception to this is a paper about the comparison of the human and chimpanzee genomes which I found interesting, lucid and helpful.

However before getting to matters-DNA it should be noted that non-genotype approaches matters are not always that good.  I have come across cited examples of other (avian) taxonomists who have looked at anatomy and :
  • "found that Otididae and Eurypygidae had double dorsal horns of spinal grey matter whereas other gruiformes examined had single horns." or
  • propose "A sister group relationship between Psittaciformes {parrots etc} and Coliiformes (mousebirds), which share a unique form of the tendon of musculus extensor digitorum longus ..." 
which both seem a long way off suggesting anything of practical importance and could thus be included in a list of unhelpful offerings. 

At a slightly less weird level of analysis it used to be suggested that the three species illustrated below (from the left, Apostlebird, Magpie-lark and White-winged Chough) could be linked together as "mud-nesters".
A quick look at the shapes of their bills might suggest they are not particularly closely related, and a knowledge of their lifestyles rapidly splits the Magpie-lark off from the other two which do still seem to be fairly closely linked, especially their life of obligate communal nesting.  This 2+1 split seems to be supported by DNA analysis.

However these apparent differences in morphology pale into insignificance when looking at a few orchid species. 
On the left we have Arachnorchis atrovespa and on the right is Stegostyla cucullata.  (Showing the difficulties with vernacular names the Field Guide offers "Thin-clubbed Mantis Orchid" for the Spider Orchid.)  About the only way I can get the Stegostyla to be a spider orchid is offered in the middle frame of the triptych.

In fairness, and fairness - with stability - is one of the key attributes needed in this debate, some of the species split out of the 'old Caladenia' are quite similar in macro-structure.
Petalochilus fuscatus, Cyanicula caerulea, Stegostyla moschata.  Colour is a rough guide, but some Petalochilus can be quite white and pink 'Stegs' are also evident in the field.  Cyanicula is always blue (incidentally the word 'Cyanicula' appears in the Plantnet listing when searching for the genus 'Caladenia'- go figure).

Where I will end up in this post is to conclude that there are many characteristics that can be looked at when defining the taxonomy of things.  It is very dangerous to focus on just one technique.  Other aspects of the debate, involving inter alia such little known taxonomists as  Hans Christian Andersen, Burt Lancaster, the Brothers Grimm and Danny Kaye, will follow.

1 comment:

Judith Gray said...

All I can say, is that I am glad that it wasn't me trying to define the categories. I find it hard enough to learn the scientific names and id plants in particular. Very interesting thoughts though about something which could be quite complex I imagine.