Flower frog
A weighted holder that sits in the bottom of a vase or bowl to keep flower stems upright.
Also: frog
A flower frog is any reusable device that holds stems in position under water. Some are glass or ceramic domes with holes. Some are metal cages or loops of wire. The pin type, a heavy base with upright needles, is the Japanese kenzan. Frogs were common in homes in the early 20th century and fell out of use when floral foam arrived. They have come back as florists look for ways to work without plastic.