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Spiraea alba

Identity

Common name: White meadowsweet
Origin: North America
Plant type: Shrub
Life cycle: Perennial
Code of conduct: Annex II
Invasive status (ISEIA protocol): Black list
Main ornemental function: Ornamental shrub

Description

This factsheet is common for 3 species of North American Spiraea's : S. alba, S. douglasii and S. x bilardii. These are rhizomatous shrubs, with a height of 1 to 2 m, multi-stemmed, rising at the base. Forming single indivuduals or dense thickets. S. alba has small white flowers, grouped in dense conical panicles. Single leaves, toothed all along the edge.

Spread

In Belgium, reproduction modes of North American Spiraea's probably vary with species and environment. S. alba and S. x billardii seem to reproduce only vegetatively by rhizomes and sprouting. Rhizomes can extend to several meters from the parent plant. No seed germination have been observed in controled experiments. Cutting is also metionned in litterature. Small rhizome fragments (10 cm long) can regenerate at a rate of 20% for S. Alba. These fragments can be transported over long distances through rivers or soil transport.

Habitat

North American spiraea's colonise riverbanks, wet woodlands, clearcuts, forest edges. They grow on sandy or loamy soils, rather moist and acidic. S. alba is mostly found along linear networks (roadways, waterways, hedges). Also planted in garden and parks.

Impact

Species classified A2 in Belgium. Spiraea are fast-growing rhizomatous species with high lateral expansion capacities. They easily form dense monospecific thickets which outcompete native flora and may reduce plant diversity. The species can colonise habitats of high conservation value like riverbanks and alluvial forests. In the Ardennes (Southern Belgium), a population of S. alba has spread in a Natura 2000 forest from a few deliberately planted individuals to an invaded area of more than 3 ha along rivers. Few native species can grow under this dense shrub layer, which prevent trees from regenerating. Other Spiraea species have been reported as invasive or potentially invasive in Europe, like Spiraea tomentosa or Spiraea japonica. But these species are not included in the list of invasive plants in Belgium. For more information about this species, click here

Recommendation

(1) Avoid planting this species near rivers and wet habitats, especially in the vicinity of protected areas (natural reserves, Natura 2000 sites, etc.) ; (2) put a rhizome barrier in order to limit lateral expansion.

Possible native alternative

Main ornemental function

Ornamental shrub

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