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Re: 23 species or less?

  • Subject: Re: 23 species or less?
  • From: "W. George Schmid" <hostahill@msn.com>
  • Date: Sat, 2 Mar 2002 10:04:47 -0500

Thanks for your comments which are congruent with my investigations. I am not certain about hexaploidy because none has shown up to my knowledge. It is possible, of course, that it exists. Maybe Ben has found evidence of it. Your statement concerning the breakdown of discontinuities between specific populations is exactly what I described in my book back in 1991. Flower morphology indicates that there may (originally) have been a half dozen good species which have been shuffled around over the last millennium. We have records of Japanese gardeners and florists doing just that. Still, isolated populations do exist in remote areas of Korea as Chung described. In the Japanese archipelago the facts are not quite so easy to establish. It is a mess. Part of what created these problems may be allopolyploidy. The reduced fertility of some of Maekawa's species (like (H. nigrescens) point to this. We should also consider that segmental allopolyploidy may be the cause of reduced fertility. I do believe that your conclusion about the ancient progenitors being amphidiploids is correct. After all they behave like diploids and seem to form only bivalents at meiosis. In the populations I have field-investigated a high degree of fertility seems to have been maintained. Because of the breakdown of discontinuities (caused by a number of factors) rampant interspecific hybridization has occurred. In many cases, these populations show an obvious mix of macromorphological traits. Notwithstanding, these populations have apparently maintained their gene pool quite successfully and over some time, judging by specimens examined which date back 100 years and some taken recently. I realize, of course, that a century is a very short period for gene flow.
What disturbs me is that too much emphasis on molecular investigations (DNA content) may lead to an undue contraction of the number of species we have. One example is the reclassification of H. montana (as proposed by Fujita), a species found all over the Japanese archipelago including Hokkaido, under H. sieboldiana, a species widespread in gardens the world over but rarely seen in the wild. In fact many of the synonyms listed for H. sieboldiana by many botanists are now known to be hybrids made in Europe after 1832. There are a very large number of clearly defined included macromorphological differences between the two. I agree that they are related in some way - I placed them in the same section), but the latter is documented only by Fujita as H. sieboldiana var. glabra, occurring as a very limited population in southern Japan. When I researched data for my book, I was able to inspect all of the specimens collected from all herbaria assembled at by the University of Georgia. Of the "standard" H. sieboldiana but most were collected in gardens and some collected in the wild had no number nor geographic information. Many, who have explored Japan have not seen the typical (European) H. sieboldiana in the wild.
Linne started the systematic botany so that we can easily identify plants and the recognition concept of species definition can not be thrown out just because DNA content may show certain relationships. Having said that, molecular biology will yield valuable clues to the solution of this gigantic puzzle but to consider it apart from all other methodologies reduces its importance.
W. George Schmid
----- Original Message -----
From: halinar@open.org
Sent: Saturday, March 02, 2002 12:08 AM
To: hosta-open@mallorn.com
Subject: Re: 23 species or less?

>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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