Syringa (Lilac) is a genus of about 20–25 species of flowering plants in the olive family (Oleaceae), native to Europe and Asia.Flora Europaea: SyringaFlora of China: SyringaFlora of Pakistan: SyringaGermplasm Resources Information Network: Syringa

The genus is most closely related to Ligustrum (privet), classified with it in Oleaceae tribus Oleeae subtribus Ligustrinae.University of Oxford, Oleaceae information site: New classification of the Oleaceae

Lilacs are used as food plants by the larvae of some Lepidoptera species including Copper Underwing, Scalloped Oak and Svensson's Copper Underwing.

Species

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Cultivation and uses

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. If pruning is required, it should be done right after flowering is finished, before next year's flower buds are formed. Lilacs generally grow better in slightly alkaline soil.

Lilac bushes can be prone to powdery mildew disease, which is caused by poor air circulation.

The wood of lilac is close-grained, diffuse-porous, extremely hard and one of the densest in Europe. The sapwood is typically cream-coloured and the heartwood has various shades of brown and purple. Lilac wood has traditionally been used for engraving, musical instruments, knife handles etc. When drying, the wood has a tendency to be encurved as a twisted material, and to split into narrow sticks. The wood of Common Lilac is even harder than for example that of Syringa josikaea.