Syringa (Lilac) is a genus of about 20–25 species of flowering woody plants in the olive family (Oleaceae), native to woodland and scrub from southeastern Europe to eastern Asia, and widely and commonly cultivated in temperate areas elsewhere.
The genus is most closely related to Ligustrum (privet), classified with it in Oleaceae tribus Oleeae subtribus Ligustrinae.
Lilacs are used as food plants by the larvae of some Lepidoptera species including Copper Underwing, Scalloped Oak and Svensson’s Copper Underwing and Saras.
They are small trees, ranging in size from 2 to 10 metres tall, with stems up to 20 to 30 centimetres diameter. The leaves are opposite (occasionally in whorls of three) in arrangement, and their shape is simple and heart-shaped to broad lanceolate in most species, but pinnate in a few species. The flowers are produced in spring, each flower being 5 to 10 millimetres in diameter with a four-lobed corolla, the corolla tube narrow, 5 to 20 millimetres long; they are bisexual, with fertile stamens and stigma in each flower. The usual flower colour is a shade of purple (often a light purple or lilac), but white, pale yellow and pink, and even a dark burgundy color are also found. The flowers grow in large panicles, and in several species have a strong fragrance. Flowering varies between mid spring to early summer, depending on the species. The fruit is a dry, brown capsule, splitting in two at maturity to release the two winged seeds.