The native state flower is Hibiscus Brackenridgei, the yellow hibiscus.

Yes that is the state flower. I don't know what exactly they use to symbolize H. brackenridgei but usually people may use any yellow cultivar of the common H. rosa-sinensis. Otherwise, H. brackenridgei (ma'o hau hele) should be used as a symbol for our state. The only drawback to H. brackenridgei is its coarse texture, and its appearance which may not be as attractive (depending on opinion) as the H. rosa-sinensis cultivars. It is best grown as a specimen plant reaching large shrub to small tree size. If conditions are favorable (dry, and with the right soil) the plant will have much smaller leaves, the branch structure will appear more compact, and the plant will be shorter. It is possible to prune this species. Many books (e.g. books on the states of the U.S.) have pictures of hybrid red and yellow hibiscuses for Hawai'i's state flower. The state flower was formerly Hibiscus kokio (Koki'o'ula'ula) but in many books and to many people the state flower was known as the red hibiscus (probably H. rosa sinensis. Some books just say Hibiscus). Today H. brackenridgei is the state flower, but even in Hawai'i most people may often think of any yellow hibiscus as our state flower.

Any yellow Hibiscus (usually in the H. rosa-sinensis species) with flowers about 4-6 inches long is usually used as a substitute for H. brackenridgei.