I've got yellow Yarrow in my garden and have been looking for a white
variety. I've come across 2 possibles:

Achillea grandifolia
http://www.highwaygold.co.uk/science.../PIC00027.html,
or
Tanacetum macrophyllum http://www.cfgphoto.com/details.php?image_id=2923

Are these both the same plant? - they look identical to me.