Cypress spurge is an herbaceous perennial with thickly clustered stems typically growing no higher than 16 in (40 cm) tall. It has deep vertical roots as well as extensive creeping lateral roots that produce adventitious buds. Leaves are green, alternate, stalkless, and very narrow. They have smooth margins and are clustered tightly on plant stems. Flowers are tiny, lime green, and enclosed by showy, yellow-green bracts. They are arranged in clusters at stem tips. Seed capsules contain three smooth, oval, gray-brown seeds.