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Plant descriptive data is much to complex to be captured in XML which is more geared towards presentation than representation.

I'll second that. I use LaTeX, and previously used a precursor to SGML, to typeset all my printed documents. These *typesetting* languages are great for defining the appearance of the content of documents, but they are utterly inadequate for representing the content (ie., data) itself.

This is not my understanding at all...

I thought the theory behind XML was to describe content, structure and relationships of data elements, quite independently of presentation as with typesetting languages...

Having defined an issue with XML, or similar, you can present it however you want...

Having defined an issue with a typesetting language, all you can do is typeset it...

jim