plant reproduction

David Hershey dh321 at excite.com
Mon Jan 13 18:19:19 EST 2003


Species with separate male and female individuals are termed dioecious
and comprise about 4% of seed plants, including quite a few
economically important plants. Other dioecious species are gingko,
cycads, yews, tree of heaven, pistachio, kiwi, persimmon, date palm,
fig, bittersweet, spinach, asparagus and marijuana.

Some dioecious species, such as persimmon, fig, and some hollies, can
set seedless fruit without pollination, a process called
parthenocarpy.

Even when male plants are planted close by, female plants may not set
fruit if the conditions are not favorable for cross-pollination, such
as cold or rainy weather that discourages insect pollination.

Only one male clone of Encephalartos woodii exists. It may have arisen
as a natural hybrid so maybe no females ever did exist. E. woodii
produces offsets readily so is in no imminent danger of dying out.
Many (one estimate is 500) botanic gardens and private collections
have specimens. There are botanists working to either induce a sex
change in E. woodii to produce a female or cross breed E. woodii with
a closely-related species and then backcross to eventually produce a
nearly pure E. woodii female. However, even those approaches would not
create a new clone, merely allow seed propagation of the existing
clone.

Reference

SEX CHANGE IN CYCADS - HOPE FOR WOODII? 
http://www.plantapalm.com/vce/biology/sexchange.htm


Monique Reed <monique at mail.bio.tamu.edu> wrote in message news:<3E230A72.1A728E9 at mail.bio.tamu.edu>...
> Yes, in some species there are separate male and female plants. 
> "Separation distance" (to coint a phrase useless outside this thread :
> -) ) depends on the mode of pollination.  It has to be as far as a
> pollinating insect will go, or as far as water can carry pollen.  In
> the case of wind-pollinated plants, it can be a very long distance
> indeed.
> 
> Case in point:  College Station, TX is up to its ears in yaupon holly,
> a species with separate female and male plants.  It's insect
> pollinated.  Because there's so much around, nothing is out of bug
> range and every single female will always have fruit, even if there
> isn't a male in sight.  If it were a more uncommon species, some truly
> isolated females might go unpollinated. 
> 
> Case in point:  Encephalartos woodii, a poor cycad with only a few
> remaining specimens, all of them male.  Without any females, no
> reproduction. Last time I checked the literature, they weren't having
> much luck tissue culturing or vegetatively propagating this handsome
> plant, but that may have changed by now.
> 
> Monique Reed
> 
> cra2 wrote:
> > 
> > Sorry to bother you, but I have a curiousity about sexual reproduction in
> > plants and so far I've not been able to find an easy answer.
> > Because I'm not a botanist myself, most of the websites I visit are over my
> > head and I'm unable to "weed" out the answer I'm looking for.
> > 
> > Some plants have only male or female sex organs, right?
> > These need a plant member of the opposite sex nearby in order to reproduce,
> > right?  (a bee or the wind distributing the pollen, for example)
> > 
> > Does that mean that if I were to isolate a female plant (by moving it far
> > enough away from any males for example), it would not be able to reproduce?
> > 
> > How far is far enough?  Do plants need a "mate" in the same yard?  Same
> > neighborhood?  Same state?  Same country?
> > 
> > Thanks so much!
> > cra2 "at" mindspring "dot" com



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