Sentence:  With fresh material, taxonomic conclusions are leavened by recognition that the material examined reflects the site it occupied; a herbarium packet gives one only a small fraction of the <WSD>data</WSD> desirable for sound conclusions. Herbarium material does not, indeed, allow one to extrapolate safely: what you see is what you get... 
Meaning of the word marked with <WSD> tags:  Information, especially in a scientific or computational context, or with the implication that it is organized.