Azasa
"Azasa" is an ancient flower that has been blossoming since the age of the Man'yōshū, and is now designated as a quasi-endangered species.
There are theories for how it got its name, including that it is called "azasa" because it "blossoms shallowly (asaku saku)" at shallow watersides, and that it "blossoms early in the morning (asa hayaku saku)", then "asasa", and finally became "azasa".
"Azasa" is a perennial aquatic plant that produces yellow blossoms from early May to around October.
Azasa has multiple lacy pleats around its 5 petals, and is called the "phantom flower" because not only does it blossom early in the morning then withers at around noon but also it can hardly be seen unless the morning air temperature reaches above 20 degrees.
