oak bark = Quercus species? wich one to use?

I am making a list of all the herbs and translating them into Dutch. But I have been having some trouble.


http://en.wikipedia.org/wiki/List_of_Quercus_species


is a list of the Quercus species. The book says it's a Oak Bark, But how come I get all these results. When I want do some shopping I don't want to confuse the people who sell herbs/plants/seeds.

The oak bark = Quercus robur, why doesn't the book just say Quercus robur, why does it write Quercus species?

I always check google and this dutch site
http://www.provmak.nl


(Here are others I am having trouble finding the right name
Euphrasia officinalis
Viburnum trilobum; V.opulus
Zanthoxylum americanum
Stillingia sylvatica)

the reason I am using Latin names is sometimes the translation of the English word get's me different results.

too bad the book doesn't include pictures with info that would have been so NICE!