Also called a flower frog, kenzan (剣山) literally means "sword mountain" and are devices used in the centuries-old Japanese art of flower arrangement, ikebana. 

A heavy lead plate with erected brass needles where the flower stems are fixed, the spikes pierce through and hold them in place. Introduced by the Moribana style of ikebana, kenzan are often used as an eco-friendly alternative to flower foam.

Please measure your vessel prior to purchase to ensure the kenzan will fit at the base.