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Clethra arborea

Evergreen shrub or small tree, of leaves grouped in the branches’ termination, and aromatic white flowers arranged in pendulous racemes.

Scientific nameClethra arborea Aiton

Common name: Lily of the Valley Tree


Status in Portugalinvasive species (listed in the Plano regional de erradicação e controlo de espécies de flora invasora em áreas sensíveis)

Risk Assessment score: (in development)

Last update: 01/07/2014


How to recognise it

Shrub or small tree up to 8 m, with a smooth, greyish or brownish  rhytidome.

Leavesoppositeoblanceolate to obovate, with 9-12 x 4-5 cm, acute, lustrous, serrate, pale green and glabrous on the upper surface, pubescent on the lower surface, with a short petiole, reddish and pubescent.

Flowers: very aromatic, white, with 1-2 cm diameter, hermaphrodite, arranged in simple or ramified pendulous racemes.

Fruits: brownish capsules, very small (3,5 mm), densely pubescent.

Flowering: August to October.


Characteristics that aid invasion

It reproduces by seed; producing many seeds that are easily dispersed by wind.

Native distribution area

Portugal (Madeira archipelago).


Distribution in Portugal

Azores archipelago (island of São Miguel).


Geographic areas where there are records of Clethra arborea

Introduction reasons

For ornamental purposes.


Preferential invasion environments

Ravines, roadsides and banks of watercourses.

It also invades natural areas.

Impacts on ecossystems

The rapid growth leads to the formation of dense areas that may inhibit the development of native vegetation.


Controlling an invasive species demands a well-planned management, which includes the determination of the invaded area, identifying the causes of invasion, assessing the impacts, defining the intervention priorities, selecting the adequate control methodologies and their application. Afterwards it is fundamental to monitor the efficiency of the methodologies and recuperation of the intervened area as to perform, whenever necessary, the follow-up control.

The control methodologies used for Clethra arborea include:


Physical control

Hand pulling: preferential methodology for seedlings and small plants. When in more compacted substrates, hand pulling must be made during the rainy season as to facilitate the removal of the root system.


Physical + chemical control

Cut stump method. Cut the stems as close to the ground as possible and immediately (in the following seconds) apply herbicide (active substance: glyphosatetriclopyr) to the cut stump.


Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.

Silva L, Tavares J, Smith CW (1999) Luta química contra Clethra arborea, uma invasora em São Miguel. In: IV Encontro Nacional de Protecção Integrada, 3 e 4 de Outubro de 1997, Universidade dos Açores, Angra do Heroismo, Açores, pp. 439-445.

Silva LFD (2002) Azorean introduced plants: Global characterisation and a study case – Clethra arborea (Clethraceae). Proc. Workshop on invasive">Invasive Alien species">Species on European Islands and Evolutionary Isolated Ecosystems and group of experts on invasive alien species. Council of Europe, IT-PVS/INF 33: 21-22.

Moniz J, Silva L (2003) Impact of Clethra arborea Aiton (Clethraceae) in a special protection area of São Miguel island, Azores. Life and Marine Sciences, 20A: 37-46.