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Re: Fern apogamy


Dear Tony,
	Fern hybrids are not straight forward.  Species do not hybridize in 
nature because the parents are separated in a way that prevents their 
eggs and sperm from meeting.  In habitats where members of the same 
genera occur together, hybrids between parents with the same number of 
chromosomes are likely to be fertile.  When the parents have differing 
chromosome numbers, as is generally the case, hybrids will mostly be 
sterile.  In fact, the standard diagnosis for a hybrid specimen is the 
presence of malformed spores.  These plants might escape their 
infertility by ocassional, sporadic apogamy, but most do not, or the 
world would be overrun by them.

	An example of a hybrid that has escaped the infertility trap:  The 
genetic compliment of Dryppteris goldiana includes two copies of each 
chromosome, it is a diploid.  Dryopteris cristata has four copies of 
each chromosome, and it is a tetrapolid.  The hybrid of the two is a 
triploid  with three copies of  each chromosome, one from D. goldiana, 
and two from D. cristata.  Thus, meiosis cannot function properly, and 
it is a sterile hybrid.  The plant we call Dryopteris clintoniana is 
referred to as the hybrid, but in fact the species is derived from one 
or more triploid hybrids where one or more mother cell has undergone a 
doubling of chromosome number from 3 to 6.  The resulting hexaploid 
cell(s) successfully underwent meiosis and produced mature spores that 
germinated and were fertilized to produce a fertile hexaploid plant.   
Further rounds of reproduction have produced the species as we know it.

	Something like this may have happened with your Cyrtomium hybrid.  
Perhaps it is functioning as a normal species, and that is whyit is  
not uniform in propagation.  You might find it interesting to explore 
the subject of fern hybrids in David Lellinger's  Field Manual of Ferns 
& Fern Allies of the United States and Canada (1985, Smithsonian 
Press).    There are extensive notes on hybrids between native species 
in the individual plant descriptions, and diagrams and discussions of 
the hybrid groups in the back.


Hope this  helps

Betty in South Bend IN
where snow is melting before the next cold breeze arrives.



On Jan 9, 2005, at 10:29 AM, Tony Avent wrote:

> Fern Growers:
>
> 	I have been studying the list of apogamous ferns that Tom posted last 
> week
> and have a question.  We are growing a hybrid cyrtomium, C. falcataum 
> x C.
> caryotideum.  We received our original plant from Sue Olsen several 
> years
> ago.  Both species are listed as apogamous with C. falcatum swinging 
> both
> ways.  I would expect the hybrid to be apogamous also, but when we grew
> spores from the original hybrid, the offspring varied widely.  Most 
> fern
> hybrids that we have tried to grow from spores are sterile, and the few
> that are fertile ones appear to be apogamous.  Are their other cases in
> which fertile fern hybrids are not apogamous?
>
> Tony Avent
> Plant Delights Nursery @
> Juniper Level Botanic Garden
> 9241 Sauls Road
> Raleigh, NC  27603  USA
> Minimum Winter Temps 0-5 F
> Maximum Summer Temps 95-105F
> USDA Hardiness Zone 7b
> email tony@plantdelights.com
> website  http://www.plantdel.com
> phone 919 772-4794
> fax  919 772-4752
> "I consider every plant hardy until I have killed it myself...at least
> three times" - Avent
>
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