Of the approximately 140 species, nearly all are
shrubs less than tall, but a few qualify as
trees, the largest reaching . Both
evergreen and
deciduous species occur, in tropical and temperate regions respectively. The
leaves are lanceolate in most species, and arranged in opposite pairs on the stems (alternate in one species,
B. alternifolia); they range from long. The
flowers of the Asiatic species are mostly produced in terminal
panicles long; the American species more commonly as cymes forming small, globose heads. Each individual flower is tubular and divided into four spreading lobes (
petals) about across, the
corolla length ranging from around 10 mm in the Asiatics to 3–30 mm in the American species, the wider variation in the latter because some South American species have evolved long red flowers to attract
hummingbirds, rather than insects, as exclusive
pollinators. The colour of the flowers varies widely, from mostly pastel pinks and blues in Asia, to vibrant yellows and reds in the New World, while many cultivars have deeper tones. The flowers are generally rich in
nectar and often strongly honey-scented. The
fruit is a small
capsule about long and diameter, containing numerous small
seeds; in a few species (previously classified in the separate genus
Nicodemia) the capsule is soft and fleshy, forming a
berry. ==Distribution==