The dayflower, or spiderwort (Commelina Communis) is a weak-stemmed herb of sprawling habit and small blue flowers which was used to produce a dye for cloth. As the common name, and the poem, implies, the flowers and the colour from the dye fade quickly. This poem appears in almost identical form in the Man’yōshū (MYS VII: 1351) and an alternative reading is to see the dayflower as a metaphor for a lover:

Fickle one,
I loved you.
Though I knew
Your heart
Would soon shift to another