Persian lilac vs syringa

Persian lilac

noun
  • Syringa × persica, a shrub in the olive family (Oleaceae) 

  • Melia azedarach, a tree in the mahogany family (Meliaceae) 

syringa

noun
  • Any of several flowering plants, of the genus Syringa, such as the lilacs. 

  • Hence any of several flowering plants of the genus Philadelphus, such as now in the Western United States Philadelphus lewisii. 

How often have the words Persian lilac and syringa occurred in a corpus of books? (source: Google Ngram Viewer )