Gardeners love summer-blooming shrubs, and a dandy for our region is the Lilac Chaste Tree, scientific name Vitex agnus-castus. Often it is called just “Lilac,” but that common name is more correctly attributed to the bush with the scientific name Syringa vulgaris. There are vast differences between the Lilac Chaste Tree, Vitex, and the Lilac bush, Syringa.