Purely non-sexual reproduction

[Jochen Katz]

I am aware that there are certain species [plants and animals]
which do at times reproduce non-sexual, but have nevertheless
the capability of reproducing sexual and depends on the environment
which route is chosen. And as such there is the gender polarity.

But I was wondering if there are any organisms which do reproduce
purely non-sexual?  Whether "higher" species, or just microorganisms
or plants.  

I would be greatful for some information on any kind of life that 
reproduces purely non-sexual and where there is only "one kind"
of it.

I am not a regular reader on this group and would be grateful if 
you could also email me your response so that I don't miss it
accidentally.

Thank you very much.

Jochen Katz
jkatz at math.gatech.edu