Buddleja davidii is a shrub between 1 and 5m in height with widely spreading branches. The foliage is semi-erect to falling. Quite flexible quadrangular branches. Leaves: opposite, lanceolate, from 10 to 30cm length with slightly toothed edges, upper face dark green and shiny, lower face white with downy hairs. Flowers: gathered in dense and pointed inflorescences approximately 35cm long. Small, (10mm X 3mm) scented hermaphrodite flowers. Corolla in the shape of tube which ends in 4 lobes, coloured white to crimson according to the varieties, with an orange stain in the centre. Flowering from July to October in Europe. Fruit is small, 8mm long capsules. Fruiting from September to December in Europe.

Its delicate perfume attracts butterflies.

Seeds can remain dormant in the ground for many years. Buddleia is able to colonise a new zone in one to two years from seeding. A shrub can flower and bear fruit in the first year. It can reach a height of 2 metres one year after being cut at the base. Buddleia is a coloniser of short lifespan (the oldest individual having been found is 37 years old). The largest densities of invasion would normally be observed in the first ten years.

This plant is appreciated as an ornamental, and is planted in hedges and other borders.

Buddleia usually occurs in open and disturbed sites like railways, the edges of roads, walls, cliffs, building sites, waste lands and ruins. It typically colonises river banks at altitudes of 2000m or more. Sometimes it is found in forests.

Buddleia davidii is pollinated by insects, in particular butterflies.

Dense infestations of Buddleia compete with indigenous vegetation of rivers and impede the growth and reproduction of other species of trees and shrubs. Monospecific stands of Buddleia impede access to rivers. Seedlings, which have superficial rooting, are easily carried away in floods and may form blockages, causing erosion of banks.

Preventative measures: A Risk Assessment of Buddleja davidii for Hawai‘i and other Pacific islands was prepared by Dr. Curtis Daehler (UH Botany) with funding from the Kaulunani Urban Forestry Program and US Forest Service. The alien plant screening system is derived from Pheloung et al. (1999) with minor modifications for use in Pacific islands (Daehler et al. 2004). The result is a score of 13 and a recommendation of: \"Likely to cause significant ecological or economic harm in Hawai‘i and on other Pacific Islands as determined by a high WRA score, which is based on published sources describing species biology and behaviour in Hawai‘i and/or other parts of the world.\"

\r\nBiological: Researchers in New Zealand are currently studying the possibility of biological control with the coleopter Cleopus japonicus. \r\n

\r\nIntegrated management: Management methods such as digging it out are applicable only to minor infestations at the initial stage of invasion. Cutting inflorescences before they bear fruit is a preventative technique, which makes it possible to limit the production of the seeds. Disturbances caused by uprooting young Buddleia shrubs actually assist its development. After uprooting, planting alternative species is recommended. It is necessary to remove uprooted plants which can grow as cuttings. When it is cut, Buddleia grows back from the stump very vigorously. Cutting must be carried out at the base of the seedling and be accompanied by an immediate white-washing of the stump with a systemic weedkiller.