SeeBelow Nut writes:

>Jeffrey Turner wrote:
>> 
>> I have noticed the existence of stemless dandelions, ostensibly driven
>> by the advantage of being lower than lawn mower blades.  Has this
>> phenomena been published?  I'm neither a botanist nor biologist and am
>> curious about this, can anyone give me some information?  Thanks.
>
>I agree with your hypothesis.  I would be surprised if no one has
>researched this before, but perhaps no academic type has paid attention
>to his lawn.

The effect is well known and has been noted for at least two hundred years.
While your observations are to be commended -- and there is undoubtedly a form
of selection going on -- the effect is almost certainly wholly epigenetic. It
is not likely to be the result of the mower's direct selection for that certain
percentage of the dandelion population that flowers lower to the ground and is
thus not heritable variation.

When plants are stressed, they switch from vegetative to reproductive
(flowering) growth patterns. While this stress is most normally induced by
drought, any form of stress: mechanical mowing, herbivory, disease, etc. may be
sufficient to switch the plant into a "desperation" strategy of
attempting to
create one last sexually diverse generation of seeds before the parent plant
expires.

Horticulturalists have long used this effect to time fruit set in their crops.
Although the short note below contains a number of misspelled words, the author
very clearly conveys the commonality of the knowledge:

  http://plant-tc.coafes.umn.edu/listserv/2003/log0308/msg00113.html

If you go to Google and type in the phrase:

  stress plant switch vegetative reproductive

you'll find hundreds of pages explaining the phenomenon. Perhaps more
importantly, there have been tens of thousands of papers published on the
subject, particularly in agronomy and horticulture.

Wirt Atmar
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