low copy number housekeeping genes - (Mar/13/2015 )

Hi all, 

Do the housekeeping genes in plants like ubiquitin, alpha tubulin etc. exist in low copy numbers? They are called reference genes but can they be used in confirming a  substance as plant material?

Thanks

only genes for materials found exclusively in plants (preferably all plants) can be used to confirm a substance as plant material. ubiquitin, alpha tubulin, and the like are found in animal as well as plant cells.

Thanks, but anyone know examples for single copy genes specific to plants?