What is "ceanothus thyrsiflorus"

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).

Ceanothus thyrsiflorus, known as blueblossom or blue blossom ceanothus, is an evergreen shrub in the genus Ceanothus that is endemic to California. The term 'Californian lilac' is also applied to this and other varieties of ceanothus, though it is not closely related to Syringa, the true lilac.