Yoshino's death. His beautiful wife died, so now there are no more cherry blossoms.
plum, peach and cherry blossoms: first two held in high regards by Chinese as signs of eternity; latter one on one hand has to do with vanity and death, and on the other hand with the Japanese trying to establish their cultural independence.
Legend has it that the rat was first because he hitched a ride on the ox who was in the lead, but jumped off the ox and became the first animal of the zodiac. (According to issoan)