any species reproduce only asexually?

Monique Reed monique at mail.bio.tamu.edu
Thu Aug 8 09:17:53 EST 2002


All true.  One class of plants that seems to be fine without sex
includes introduced exotic weeds.  The U.S. is reluctant home to
dozens of species (many of then aquatic) that reproduce sexually and
vegetatively in their native regions but which apparently lack the
proper conditions or pollinators in their introduced ranges.  You can
look in manuals and floras and find "flowers not seen" and "fruit
unknown" and "our plants apparently sterile" in the listings for
things. 

Sometimes the mode of introduction can determine whether an exotic
species has all its reproductive options or not:

One case I have experience with involves _Lycianthes asarifolia_, a
fairly attractive, wild-ginger-like groundcover from South America.
There was a population in Louisiana which was apparently the result of
a single vegetative introduction.  Since the plants are
self-infertile, it takes two plants to tango and the LA population
flowered but never produced mature fruit; it was clonal in nature. The
population was rolling merrily along via only vegetative means until
it was eradicated.  A few years ago in Houston, this plant was
identified from several neighborhoods.  The TX introduction must have
been from one or more fruits, because we are certainly seeing mature
fruit on these things, as well as a lot of variation in vegetative
form. Herbicides are basically ineffective in rates that won't kill
the whole yard, and it will out-compete St. Augustine in a shaded
lawn.  We will never get rid of the stuff.

Monique Reed

David Hershey wrote:
> 
> 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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