Hyakujitsuko (crape myrtle) means a flower that keeps blooming for 100 days in Japanese, and similarly, Sennichiko (globe amaranth) means a flower that keeps blooming for 1000 days. Both do not represent a specific period, but mean a flower that blooms for a long time. It is the same expression as “3000m long White hair” in Chinese poetry or “Naniwa’s 808 bridges” which means that there are many bridges in Osaka. There is a word called “Tohkako (Flowers that bloom for ten days), but this is not a specific flower name, but means “No flower keeps blooming for ten days.” and is used to express which is likened to the fragility of human life.

百日紅はサルスベリのことで、およそ百日は咲き続ける花と言うことでしょうね。それでは、千日紅は千日咲く花と言う意味かと言うと、そうではなく、百日紅よりは長く咲くとと言う意味が込められているのでしょう。いずれにしろ、百日とか千日は「長く」と言う意味で使われています。「白髪三千丈」とか「難波八百八橋」と同じ表現です。十日紅と言う言葉がありますが、これは具体的な花の名前ではなく、「花に十日の紅なし」と言う意味で、生きとし生けるものの命の儚さを表現する時に使います。