The Japanese name of this flower is "Renge". Renge symbolizes the Buddhism Paradise (Jyodo). In fact, Renge originally meant a lotus flower. Although I do not know exactly why this flower started to be called Renge, my guess is the following.

Buddha was supposedly born on April 8 bout 2,500 years ago. Around this time of a year according to the lunar calendar, flowers of Renge could be seen everywhere in Japan. This plant was grown in rice fields after the crop was harvested, since this plant solidify nitrogen in its roots, and the solidified nitrogen works as fertilizer.
On the other hand, the real lotus plant does not flower in spring in Japan.

When I see this plant, I recall my experience with a Haramatsuri on April 8.
We as children pulled a cart carrying a white elephant made of a bamboo cage covered by white paper. A small wooden shrine containing a statue of Buddha was placed on the back of the elephant.

While parading with this white elephant, we sang

    In olden day of 3000 years ago
    On April 8 in Spring
    . . .

Toshi