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Re: 23 species or less?

  • Subject: Re: 23 species or less?
  • From: halinar@open.org
  • Date: Fri, 1 Mar 2002 21:02:22 -0800 (PST)


>In my opinion, quantitative DNA content is not the sole criterion for 
>delimiting species. It is simply another measure which contributes to 

DNA content can be a factor to consider in trying to figure out which 
hostas are species and how they are seperated from each other, and it 
can be used as a factor in trying to determine if a particular plant 
is a hybrid between two species.  However, first you have to have some 
good reason to suspect that a plant is a hybrid between two species 
before the DNA content is of any value.  Second, the error in making 
the measurments has to be such that any small difference can be 
statistically significent.  Ben has given exampes where he thinks a 
particular hosta is a hybrid based on his DNA content, but he hasn't 
given any reason why he thinks the two species are the purported 
parents and he doesn't give us any idea of what his error level is.  

>Also, polyploidization is an important cause for speciation and that 
>fact is documented. Again it is not an exclusive one. For me, it 
>would be valuable to find out if the degree of ploidy in Hosta 
>correlates with macromorphological features, the ecological 
>preferences of a species and geographic distribution.

Given that hostas have 60 chromosomes would certainly suggest that 
hostas are ancient amphidiploids.  I wouldn't be surprised if hostas 
weren't hexaploids.  It could well be that present day hostas are the 
results of different polyploidization events, or it could be one 
polyploidization event which lead to all the present hostas.  The 
polyploid nature would allow for the loss or reannangements of 
chromosomes with little effect on the viability of the plants.  It 
would be interesting to plot DNA content with various other traits and 
especially geographic distribution to see what kinds of correlations 

>What makes the investigation of the genus so difficult is that the 
>discontinuities which are usually clearly definable are no longer so 
>in Hosta.

It may be difficult to really understand hosta taxonomy because hostas 
have been grown as garden plants for so long in Japan and plant 
populations have been so distrubed by human population over hundreds 
of years.  

Joe Halinar

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