Hibiscus syriacus 'Blue Bird' (Rose of Sharon) Malvaceae Kristin Yanker-Hansen, Danville. The flower shown is one of the best selections of this species with 4-inch sky-blue flowers and a small red eye. Named by Linaeus, it is an Old World plant which is cold hardy to zero or below and forms a shrub or small tree to 10 feet. Over 30 cultivars are available and it is an easily grown plant. Both single and double forms in white, through pink or rose to purple are available.