Buddleja is also seen in its own family Buddlejiaceae.
There are around 100 species (90 – 140) with none native in Australia.
A number of species, originally garden plants, have become naturalised here.
Some, especially B. davidii, have become invasive forming dense clusters.
They are mostly shrubs with a few trees and rarely, herbs.
The often sprawling shrubs can be evergreen or (semi-) deciduous.
The branches can be round or square in cross section.
Many parts may have a dense covering of hairs.
Leaves are opposite apart from B. alternifolia with alternate leaves.
On petioles, sometimes very short, they are up to 30 cm long.
The blade is mostly lanceolate but some are narrow and almost linear.
The blade is often textured with a pale, sometimes hairy, underside.
The edges can be smooth or toothed.
Small stipules are often deciduous or may be represented by a line between the petiole bases.
The terminal or axillary inflorescences are commonly branched spikes up to 50 cm long.
Spikes may have flowers for weeks as new ones open at the tip as the lower ones die.
Others species have small clusters or globular flower heads.
There are small bracts and bracteoles.
Different species have uni- or bi-sexual flowers.
The abundant nectar attracts butterflies and birds.
The bell or funnel-shaped flowers are from 0.3 to 3 cm long.
The straight or curved calyx has 4 sepals with the bases fused for around half their length.
The 4 petals commonly have a straight or curved, cylindrical corolla tube with shorter, flaring lobes.
Colours include white, pink, yellow, orange, blue, red and various shades of purple.
The 4 stamens, with short filaments, are inserted into the corolla tube.
The superior ovary has 2 locules with numerous ovules, and a short style.
The fruit are almost always small septicidal capsules, rarely berries.
The 2 chambers each contain many, often winged, seeds.
There are quite a few natural hybrids and a lot of cultivars.