The Christmas star or poinsettia is a popular houseplant. Experts told us how to choose the right plant when buying. 1. Flower Buds (Cyathia) Assess the flower buds, known as cyathia, at the tips of the shoots. Fresh buds are greenish-yellow, round and unopened. If they are covered with yellow pollen, this is a sign that the plant is not fresh and the buds may soon fall off.