"the vase of stiff anemones"
Japanese anemone (Anemone hupehensis)
Creative Commons Attribution Share AlikeJapanese anemone (Anemone hupehensis) - Credit: rebel rebel
Public Domain'Anemones' - Credit: François Barraud (1899-1934)

 Anemone is a genus of flowering plants which contains about 120 diverse species. They are sometimes known as windflowers and come in a wide variety of colours.

The genus tends to be divided into three categories: low-growing species which bloom in springtime; tuberous Mediterranean types which bloom in spring and summer; and taller species which bloom in late summer and autumn.

The description 'stiff' suggests that the anemone Daphne du Maurier has in mind may be one of the taller-growing varieties.