There are various theories as to what 'Asagao no Hana' would indicate; some say it refers to the morning glory, the rose of Sharon, the California rose and the balloon flower, but the most widely held theory is the one supporting the possibility of the balloon flower.
「朝貌の花」が何を指すかについては、アサガオ、ムクゲ（むくげ）、キキョウ、ヒルガオなど諸説あるが、桔梗とする説が最も有力である。