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© M. Halford
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Spiraea x billardii

Identity

Common name: Billardii meadowsweet
Origin: North America
Plant type: Shrub
Life cycle: Perennial
Code of conduct: Annex II
Invasive status (ISEIA protocol): Watch 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. S. x billardii is the (supposed) hybrid between S. alba and S. douglasii. Rhizomatous shrub, with a height of 1 to 2 m, multi-stemmed, rising at the base. Forming single indivuduals or dense thickets. Rose and small flowers, grouped in dense conical panicles. Leaves with intermediate traits from its two parents.

Spread

In Belgium, reproduction modes of North American Spiraea's varies with species and environment. S. alba and S. x billardii seem to reproduce only vegetatively by rhizomes, sprouting and cutting. Rhizomes can extend to several meters from the parent plant. No seed germination have been observed for this hybrid species. Small rhizome fragments (10 cm long) can regenerate at a rate of 50%, which is higher than S. alba, indicating the vegetative multiplication capacities is more important. Long distance dispersal of rhizome fragments transported by rivers stream or soil transfer is possible.

Habitat

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

Impact

Species classified B2 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. Nevertheless, Spiraea x billardii seems less detrimental in Belgium. There are few populations in natural habitats of ecological value. Important to mention there are other Spiraea species considered as invasive or potentially invasive in Europe, like S. tomentosa or S. japonica. For more information about this species, click here

Recommendation

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

Possible native alternative

Main ornemental function

Ornamental shrub

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