Alternate meaning: Lilac (color)

About 20-25 species; see text.

Lilacs (Syringa) are a genus of plants, in the family Oleaceae, native to Europe and Asia. Lilacs range in size from large shrubs to small trees, 2-10 m tall. They are often grown for the panicles of white, pale pink or more generally purple flowers. The flowers grow in large clusters, and in several species have a strong and choice fragrance. Flowering starts after 80-110 growing degree days.

Lilacs are popular shrubs in parks and gardens throughout the temperate zone. The term French lilac is often used to refer to modern double-flowered cultivars.

Lilacs flower on old wood, and produce more flowers if unpruned. If pruned, the plant responds by producing fast-growing young vegetative growth with no flowers, in an attempt to restore the removed branches; a pruned lilac often produces few or no flowers for one to five or more years, before the new growth matures sufficiently to start flowering. Unpruned lilacs flower reliably every year. Despite this, a common fallacy holds that lilacs should be pruned regularly.

A pale purple colour is generally known as 'lilac' after the flower.