The idea of using a flower name instead of a Deity or holy person is a logical one... One of the commandments is Thou shalt not take the name of thy Lord God in vain - this was often extended to the Holy Family and the Archangels. So using lily to mean the Holy Virgin was frequent - it is, after all, her flower... The rose was more often masculine or the Rose of Sharon (not the hybrid tea or floribunda variety that we are familiar with these days) - Lo, what is this rose, sprungen from Jesse's stem (Es Ist ein ros' enstprungen...)

LTS