Agave virginica

Jim McKenney
Mon, 08 Jun 2009 16:17:49 PDT
Several things in Tony’s post deserve comment. It always fascinates me to
see how different people come to very different conclusions even when they
seem to start with the same basic assumptions. 


First, I would like to raise the touchy subject of just what this word
monocarpic means. I’ve always understood the word to mean that the plant so
described dies after blooming and setting seed. Yet many of the plants
called monocarpic by some people do not die after blooming and setting seed.
The main rosette of such plants dies, but by then the plant has often
offsets  and is surrounded by offsets which perpetuate the plant. 


To me, the pup and the main plant are the same plant, pieces of one original
seedling. If you are the sort of person who regards the pup and the main
plant to be different plants, they you’ve got your argument cut out for you.


The use of this word monocarpic– whatever you think it means -  with respect
to Agave is particularly appropriate because the nineteenth century botanist
de Candolle who coined the word  used Agave as an example. As a result,
there are those who take the point of view that by definition it is correct
to call Agave monocarpic no matter what you think the word means. To these
people, that fact that the etymology of the word seems to be saying
something about Agave which is not necessarily true is irrelevant. 


As a result of all of this, many people now eschew the word monocarpic
because of the ambiguities surrounding its meaning. 


Now on to this business of the significance of hybridization to taxonomy.
Here again, where you end up in this discussion depends on where you start.
To state the argument in one of its most radical forms, there are those who
would say that the ability of two plants to cross and produce viable
offspring is evidence that they are conspecific, they are the same species
(never mind Tony’s concern about its significance at the generic level. I’m
talking about the species level).  To those who adopt this approach, what
the plants in question look like has nothing to do with it. 


One of the unresolved questions which taxonomists have to deal with is the
nature of the ranks/categories they use. There are two basic schools of
thought on this matter. One school asserts that species is a real, natural
phenomenon – that there really is something out there which corresponds to
what we call species. The other school of thought says that species is
whatever we decide it is. I’ve never seen a plausible argument from either
side in defense of the “natural” nature of genera – I think that the
consensus on both sides is that  genera are man made.  


The “natural species” point of view will be robustly rejected by those who
expect taxonomy to have some practical value in pigeonholing items. 


One result of this huge dichotomy in what people think is the proper
function of taxonomy is that parallel systems of naming coexist side by
side. To give a simple example of this, the wild typical form of Narcissus
jonquilla is known to botanists as Narcissus jonquilla (or if you prefer N.
jonquilla subspecies jonquilla). Yet in the horticultural literature, this
same plant is known – and has been known for centuries - as Narcissus
jonquilla simplex. Horticulturists like this name because it expresses what
is important to them – it distinguishes the single- flowered form (single in
the sense of normal flowered, not one flowered) from the various
double-flowered forms (those forms in which the floral parts are deformed
and multiplied). Horticulturists are concerned about a distinction which
does not even register on modern botanists’ radar. 


Finally, those plants which result from the fusion of alien genomes really
don’t enter into taxonomic discussions of the sort which are based on
traditional assumptions about shared ancestry. 


So when Tony says “Wait until they see the new x Velox...a cross of Verbena
and Phlox (reportedly a result of protoplast fusion)....we're talking
different families. That should turn the taxonomists on their heads.” he
might be right about it turning them on their heads, but if it does I’ll bet
that the turning of their heads will be the result of their being bent over
in laughter.  The little × in front of that name Velox (is there really such
a thing?) identifies that name as a nothotaxon - it tells you that it is
from a naming system which is distinct from the naming system used in
traditional botany. The feelings of traditional taxonomists  might very well
be more on the order of the feelings – not nice feelings, but undeniably
funny – you get when you visit the shabby side of town and see – well, you
see the sort of things which go on there. 



Jim McKenney

Montgomery County, Maryland, USA, 39.03871º North, 77.09829º West, USDA zone

My Virtual Maryland Garden



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