According to Popular Mechanics, the reason why so many fireworks are named after flowering plants is because they burst out of a seed, or shell. The shell houses all the ingredients necessary for the firework’s path and visual display.
Inside the typical firework is a tube full of explosive chemicals that produces the effects and colors for that display. The chemicals stuffed inside the tube would include loose gunpowder and concentrated explosive beads that the pyrotechnicians call "stars". When the stars are exploded that is what we see lighting up the sky. Inside the center of the shell is a bursting charge that is connected to a fuse that ignites the firework.
