Each rose-of-Sharon flower blooms for only a single day.
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history
槿 rarely stands alone; it occurs mainly in 木槿 (rose of Sharon), whose day-long blooms gave the classical metaphor 槿花一日 for fleeting glory. It joins the tree radical 木 with the phonetic 堇.
register
Literary and bound; appears in the plant name and classical allusions to transience, not as a free word in speech.