The Chinese or Rouen lilac is a cross between the common lilac and the Persian lilac that originated in France in the 18th century. It bears abundant fragrant purple-lilac blooms on arching branches in May. Its habit is considered more refined than the common lilac.

Members of the genus Syringa, commonly known as lilacs, are
shrubs or small trees prized for their showy and fragrant blooms in late
spring. The individual flowers are tubular in form and are borne in
large panicles. While the common name of the plant has come to define a
shade of pale purple, some species and hybrids have pink or white
blossoms. Lilacs begin to set buds for the following year shortly after
they finish blooming; if pruning is desired, it should be done
immediately after flowering to maintain flower production the next year.

Lilacs are native to cooler temperate areas of southeastern Europe
and eastern Asia with winter temperatures below freezing; there are no
lilacs native to North America. The genus includes at least 12 species
and numerous hybrids and cultivars. The Chicago Botanic Garden's
collection contains over 50 varieties of lilac and more than 800 plants.