Eryngium giganteum 'Silver Ghost'
Common Name: Giant sea holly, tall eyrngo, Miss Willmott's Ghost, ivory thistle.
Eryngium giganteum 'Silver Ghost' is a striking member of the perennial border in front of the Formal Rose Garden. Its flowers are very sharp. It is named after the British plantswoman Ellen Willmott who used to surreptiously plant its seeds in other gardens. 2020 update: It seems to have disappeared from this border (it is considered a short-lived plant.)
More about Miss Willmott
Photo from the Garden by Lyn Anderson