any species reproduce only asexually?

David Hershey dh321 at excite.com
Wed Aug 7 19:44:28 EST 2002


My statement, "Plants that cannot sexually reproduce at all are fairly
rare.", is consistent with Monique Reed's comments that many plant
species mainly reproduce asexually. However, they usually also have
the ability to sexually reproduce even if they rarely do. Potatoes
have an excellent method of asexual reproduction but occasionally
reproduce sexually. In 1872, Luther Burbank found a rare seed ball
from an 'Early Rose' potato. One of the seedlings became the 'Burbank'
potato which later mutated to produce 'Russet Burbank'.

With over 250,000 plant species and over one million cultivated
varieties (cultivars), there can be hundreds of examples of even a
"fairly rare" plant phenomenon. If you believe plant species incapable
of sexual reproduction are not rare, then please name several hundred
examples.
 
Most horticultural plants that multiply by division, such as
chrysanthemums, iris, daylilies and peonies, are also capable of
setting seeds if properly pollinated. Breeders use sexual reproduction
to obtain new cultivars of these and many other plants. Gardeners
usually remove the faded flowers before seeds are formed. Just because
a cultivated plant does not usually produce seeds does not mean that
it is incapable of sexual reproduction.

Of course asexual reproduction or cloning is the preferred method when
horticulturists propagate plants. One of several reasons why cloning
is preferred is because they want exact copies of superior cultivars,
not the variation that often occurs in seedling offspring. Sexual
reproduction is still important in breeding of virtually all
cultivated plants and commercial propagation of bedding plants,
vegetables, forest trees and cereal crops, such as corn, wheat and
rice.

There are some major differences between plant propagation, which is a
human activity, and plant reproduction, which plants do naturally.
This thread asked about plant reproduction. Tissue culture and
grafting are plant propagation methods but plants do not reproduce
themselves by tissue culture or grafting. Cutting propagation is very
common but few species that are propagated commercially via cuttings
naturally reproduce via cuttings. It is doubtful if a mutant plant
like the original seedless navel orange would still be in existence if
people had not propagated it by grafting.

Most polyploid plants are capable of sexual reproduction. It is just
odd number polyploids, such as triploids (3N), that are usually
sterile. The more abundant even number polyploids, such as tetraploids
(4N) and hexaploids (6N), are usually fertile. Estimates are that the
majority of flowering plant species and about 95% of fern species are
naturally polyploid.

References

Hartmann, H.T. et al. 2001. Plant Propagation Principles and
Practices, 7th edition. New York: Prentice Hall

Reilly, A. 1978. Park's Success With Seeds. Greenwood, SC: Geo. W.
Park Seed. Co.

U.S. Forest Service. 1974. Seeds of Woody Plants in the United States.
Ag. Handbook 450. Washington, DC: USDA.

Luther Burbank and Russet Burbank potato:
http://radio.boisestate.edu/projects/misc/potato/russets.htm

Polyploidy in Angiosperms:
http://www.rbgkew.org.uk/kewscientist/ks_apr98/pages/ScPap/Polyp.htm
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Polyploidy.html








"Cereoid+1+" <cereoid at prodigy.net> wrote in message news:<mb%39.416$H07.40213708 at newssvr16.news.prodigy.com>...
> Absolutely untrue.
> 
> You never heard of multiplication by division?
> 
> Most plants in the horticultural trade are propagated entirely by asexual
> means.
> 
> 
> David Hershey <dh321 at excite.com> wrote in message
> news:7039c6ef.0208061750.52c787fc at posting.google.com...
> > Plants that cannot sexually reproduce at all are fairly rare.
> >
> > There are some fern species, such as Vittaria appalachiana, that exist
> > only as tiny gametophytes, which reproduce only asexually. They never
> > form the larger sporophytes which are what we think of as the typical
> > fern plants.
> > http://www.ibiblio.org/unc-biology/herbarium/weakley/Vittar.html
> > http://www.goldsword.com/sfarmer/ATBI/gametophyte-gallery.html
> >
> > There is a cycad species, Encephalartos woodii, in which only a single
> > male plant survived in the wild. It has been reproduced by offsets and
> > still survives in many botanic gardens.
> > http://www.plantzafrica.com/plantefg/encephwoodii.htm
> >
> > King's holly (Lomatia tasmania) exists in the wild as a single
> > specimen that reproduces only asexually because it is triploid. It is
> > thought to be as much as 43,000 years old.
> > http://www.ou.edu/cas/botany-micro/ben/ben149.html
> >
> > Genetically seedless fruit, such as seedless grapes, cultivated banana
> > and navel oranges cannot set viable seed so have to be asexually
> > propagated.
> >
> > David R. Hershey
> >
> >
> > "Tristan" <hamlet2b at videotron.ca> wrote in message
>  news:<hkI39.2721$qu1.136901 at weber.videotron.net>...
> > > Hello,
> > >
> > > I have been debating with a friend about whether or not any plants
>  reproduce
> > > only asexually, or whether all plants have some mechanism of sexual
> > > reproduction.  Our research has unveiled many forms of asexual
>  reproduction,
> > > but there is usually an implication that the same plants also reproduce
> > > sexually.  Are there any species anyone knows of that reproduce only
> > > asexually?
> > >
> > > Thanks



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