simple explanation of a taxon concept

Hi all, can any of you people point me towards a web resource where one of our data managers (specialising in economic botany) can have this question answered:

I must admit I'm not altogether sure what is meant by the term taxon "concepts" (is there a simple explanation?)

I'm circulating Donald's questions around the various Kew staff who are involved in databases and some of them for some reason don't seem to have kept up with the recent fevered debate on TCS-LC and other fora

Thanks *** Sally Hinchcliffe *** Computer section, Royal Botanic Gardens, Kew *** tel: +44 (0)20 8332 5708 *** S.Hinchcliffe@rbgkew.org.uk