Invasive Alien Species in Belgium: Crassula helmsii

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Crassula helmsii - New zealand pigmyweed

Synonym:	Tillaea recurva, Crassula recurva
French name:	Crassule des étangs
Dutch name:	Watercrassula
Family:	Crassulaceae

Group:	Vascular plants
Origin:	Australia
Habitat:	freshwater
Introduction:	aquariums and ponds

ISEIA Score : 12

Naturalization in Belgium

First observation in the wild:	1982
Invasion stage:	spread
Spatial distribution:	isolated

Invasiveness

Reproduction in the wild:	yes
Dispersion potential:	high
Natural habitats:	high

More on invasiveness: New Zealand Pygmiweed colonises a wide variety of freshwater habitats with chemistry ranging from acid to alkaline, including water bodies, slow-flowing rivers, marshes and peat bogs. Due to its specific metabolism (Crassulacean Acid Metabolism), it is adapted to live in moderately fertile shallow temporary pools that experience extreme diel fluctuations in carbon availability and is able to take advantage of elevated nighttime CO2 levels. Plant ability to grow from fragments of stem enables it spread from ponds and ornamental pools into the wild. Waterfowl, mammals, downstream movement and flooding play an important role in plant dissemination. Plant fragments may also be moved with mud.

Distribution in Belgium

Established populations Biogeographic areas where the species is known to be established in the wild

	absent from district
	isolated populations (1-5 localities per district)
	widespread (>5 localities per district)

Endangered areas Biogeographic areas including Natura 2000 habitats that are likely to be invaded by the species (occurence of dense populations)

Biogeographic areas including Natura 2000 habitats that are likely to be invaded by the species (occurence of dense populations)

	low risk
	medium risk
	high risk

Endangered Natura 2000 habitats (

freshwater habitats:

3130 3150 3260 3270

Impacts on Species

Predation / Herbivory:	low
Competition:	high
Disease transmission:	low
Genetic effects:	low

Impacts on Ecosystems

Nutrient cycling:	likely
Physical alteration:	high
Natural successions:	high
Food web alteration:	low

More on impacts: Swamp stonecrop causes major environmental problems in freshwater habitats. It forms dense vegetation mats that deplete oxygen, outcompete native species and may affect the breeding success and survival of threatened aquatic plants and amphibians. Mats choke ponds and drainage ditches, impede water flow and adversely affect recreation activities.

Data Source & References

Authors:	Branquart Etienne, Stiers Iris, Triest Ludwig, Vanderhoeven Sonia, Van Landuyt Wouter, Van Rossum Fabienne, Verloove Filip
Published on:	22 November 2007
Last update:	11 December 2013

References:

Adriaens, T., Packet, J. & Denys, L. (2010)

Bestreiding over watercrassula, een lastige invasieve exoot.

Natuur.Focus 9(3): 128-129.

Booy, O., Wade, P.M. & White, V. (2008)

New Zealand Pygmyweed.

In: Invasive species management for infrastructure managers and the construction industry. CIRIA C679, CIRIA, London.

Dawson F.H. & Warman E.A. (1987)

Crassula helmsii (Kirk) Cockayne : is it an agressive alien aquatic plant in Britain?

Biological conservation 42: 247-272.

Denys, L., Packet, J. & Van Landuyt, W. (2004)

Neofyten in het Vlaamse water : signalement van vaste waarden en rijzende sterren.

Natuur.focus 3(4): 120128.

EPPO (2007)

Data sheet on quarantine pests: Crassula helmsii.

OEPP/EPPO Bulletin 37: 225-229.

Huckle J. (2002)

Invasive alien aquatic plant species, Crassula helmsii.

Invasive Alien Species Project. Fact Sheet 1. English Nature & University of Liverpool.

Keeley, J.E. (1998)

CAM Photosynthesis in submerged aquatic plants.

The Botanical Review 64(2): 121-175.

Lambinon, J., Delvosalle, L. & Duvigneaud, J. (2004)

Nouvelle fore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des régions voisines.

Editions du Patrimoine du Jardin botanique national de Belgique, Meise.

Langdon S.J. et al. (2004)

Crassula helmsii in UK ponds: effects on plant biodiversity and implications for newt conservation.

Weed Technology 18: 1349-1352.

Slembrouck J. & Molenaar E. (2001)

Crassula helmsii (Kirk) Cockayne, een nieuwe bedreiging voor onze waterflora?

Dumortiera 78: 20-23.

Van Landuyt, W., Hoste, I., Vanhecke, L., Van den Bremt, P. Vercruysse, W. & De Beer, D. (2006)

Atlas van de Flora van Vlaanderen en het Brussels gewest.

Nationale Plantentuin en het Instituut voor Natuur- en Bosonderzoek i.s.m. Flo.Wer vzw.

Verloove, F. (2006)

Catalogue of the Neophytes in Belgium (1800-2005).

Scripta Botanica Belgica 39, 89 pp.

Watson W.R.C. (1999)

Amphibians and Crassula helmsii.

Froglog 31.

Weber, E. & Gut, D. (2004)

Assessing the risk of potentially invasive plant species in central Europe.

Journal for Nature Conservation12: 171-179.