They are small trees, ranging in size from 2 to 10 metres (6 ft 7 in to 32 ft 10 in) tall, with stems up to 20 to 30 centimetres (7.9 to 11.8 in) 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 (e.g. S. protolaciniata, S. pinnatifolia). The flowers are produced in spring, each flower being 5 to 10 millimetres (0.20 to 0.39 in) in diameter with a four-lobed corolla, the corolla tube narrow, 5 to 20 millimetres (0.20 to 0.79 in) long; they are monoecious, 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.