[Taxacom] Asclepiadaceae within Apocynaceae

Kenneth Kinman kennethkinman at webtv.net
Wed Jan 28 22:16:28 CST 2009


Gurcharan recently asked:
         "Why is Asclepiadaceae merged with Apocynaceae by most authors,
and treated distinct by others?  I have to labour a lot to convince my
students who ask me justification of not recognising Asclepiadaceae with
pollinia, translator mechanism, gynostegium, monodelphous stamens and
much more as distinct family".               
*************************************************
 Dear All,
       I had a little extra time, so looked into this particular case.
Although I would sometimes be tempted to jump on this as being a case of
strict cladists merely lumping Asclepiadaceae into its paraphyletic
mother taxon Apocynaceae, it perhaps best to go along with them on this
one.                             
       Even Cronquist noted the difficulty of drawing a distinct line
between them as these  various distinctions evolved.  And Takhtajan
(1997), a morphologist, formally merged these two families.  These days
we have to choose our battles (defending paraphyletic taxa) carefully,
and this is not one that would likely be successful. 

       Since Order Gentianales only has 5 families according to the
Angiosperm Phylogeny Group, I certainly wouldn't object to resplitting
some of these large families.  However, resplitting their large Family
Apocynaceae isn't something that would probably be successful, and only
marginally useful.  In the overall scheme of things, it's frankly just a
minor nuisance compared to strict cladists placing Class Aves within the
dinosaurs (and therefore Class Reptilia).  Among angiosperms, I am much
more concerned by APG's lumping into very bloated Orders like Poales and
Malpighiales.               
           --------Ken Kinman     
P.S.   If you are really intent on maintaining a separate Family
Asclepiadaceae, you could certainly recognize a paraphyletic Family
Apocynaceae giving rise to a daughter Family Asclepiadaceae.  As someone
who does not object to paraphyletic taxa, it is certainly permissible
and justifiable.  Just not a case I would personally find important
enough to fight over compared to other higher taxa.  But here is how I
would code it in my system if you wanted to do it (the % symbol
indicating that Apocyanaceae is paraphyletic, and the coding symbol _a_
in the left-hand margin showing that Family Asclepiadaceae has a sister
group within Apocyanaceae:                                      

           Apocyanaceae%
    _a_ Asclepiadaceae







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