Back in the 1970’s there were photos from the Mid-East of Neanderthal graves with flowers in them. So this is a symbolic tradition that goes back hundreds of thousands of years.
You may be referring to the Shanigar cave used in the fiction series Clan of the Cave Bear books. It was suggested that the flowers left had herbal medical importance, so they were not merely ornamental in that case. For beauty or for utility has different connotations for human thinking processes and symbolic meaning.