What is "california lilac"

Lilac \Li"lac\ (l[imac]"lak), n. [Also lilach.] [Sp. lilac, lila, Ar. l[=i]lak, fr. Per. l[=i]laj, l[=i]lanj, l[=i]lang, n[=i]laj, n[=i]l, the indigo plant, or from the kindred l[=i]lak bluish, the flowers being named from the color. Cf. Anil.]

1. (Bot.) A shrub of the genus Syringa. There are six species, natives of Europe and Asia. Syringa vulgaris, the common lilac, and Syringa Persica, the Persian lilac, are frequently cultivated for the fragrance and beauty of their purplish or white flowers. In the British colonies various other shrubs have this name.

2. A light purplish color like that of the flower of the purplish lilac.

   California lilac (Bot.), a low shrub with dense clusters of purplish flowers ( Ceanothus thyrsiflorus).