Crassula helmsii (Kirk) Cockayne

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English New Zealand pigmyweed Status LU: established. 1st record: n/a
Lëtzebuergesch n/a Status EU: established.
Français Crassule des étangs RA: ISEIA: B0 – Alert List. Harmonia+: 0,44
Deutsch Nadelkraut Wikipedia: Wikipedia - English - New Zealand pigmyweed Wikipedia - Deutsch - Nadelkraut Wikipedia - Nederlands - Watercrassula | Wikispecies: Wikispecies - Crassula helmsii | CABI
Nederlands Watercrassula Back to the list of neophytes

Report the species

Report Crassula helmsii to the National Museum of Natural History.

Brief description

Crassula helmsii

2011, Pilley, England, UK

Crassula helmsii (Kirk) Cockayne, native to New Zealand and Australia, is an aquatic or semi-terrestrial plant that colonises a wide variety of freshwater habitats. The plant’s ability to grow from stem fragments enables it to easily spread from ponds and ornamental pools into the wild. Waterfowl, mammals, downstream movement and flooding all play an important role in plant dissemination. New Zealand pigmyweed can cause 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 recreational activities. In rivers, flow behaviour may change when the plant occurs in masses (Branquart et al. 2013).

Status and distribution in Luxembourg

Currently, Crassula helmsii (Kirk) Cockayne is not known to occur in Luxembourg (MNHNL, iNaturalist & GBIF 2020).

First reported in Belgium in 1983, this species experienced a strong expansion about 15 years later and will probably be found in other parts of the territory of the Flora. The plant is highly variable depending on whether it grows in water (aquatic phenotype) or on the banks of more or less dry ponds (terrestrial phenotype) (Lambinon & Verloove 2012).

Risk assessment

ISEIA protocol

B0 (2+3+2+3) = Alert List (Ries et al. 2013: 18).

Harmonia+ protocol

Overall risk score 0,44 = (Overall Invasion score 0,76 x Overall Impact score 0,57) (Ries et al. 2020).


Worldwide distribution


  • Branquart, E., I. Stiers, L. Triest, S. Vanderhoeven, W. Van Landuyt, F. Van Rossum & F. Verloove, 2013. Harmonia database: . Harmonia version 1.2, Belgian Forum on Invasive Species. URL: [accessed on 2020-02-28]
  • CABI, 2019. Crassula helmsii. In: Invasive Species Compendium. Wallingford, UK: CAB International. URL: [accessed 2020-02-28]
  • Lambinon J. & F. Verloove, 2012. Nouvelle flore de la Belgique, du grand-duché de Luxembourg, du Nord de la France et des régions voisines. Sixième édition. Avec la collaboration de L. Delvosalle, B. Toussaint, D. Geerinck, I. Hoste, F. Van Rossum, B. Cornier, R. Schumacker, A. Vanderpoorten et H. Vannerom. Jardin botanique national de Belgique, Meise. CXXXIX + 1195 pp. ISBN : 9789072619884.
  • MNHNL, iNaturalist & GBIF, 2020. in MNHNL-mdata, online portal combining species observation from Recorder-Lux, iNaturalist and GBIF. National Museum of Natural History, Luxembourg. URL: [Accessed 2020-02-28]
  • Ries, C., Y. Krippel & M. Pfeiffenschneider, 2020 [submitted]. Risk assessment after the Harmonia+ protocol of invasive alien vascular plant species in Luxembourg. Bulletin de la Société des naturalistes luxembourgeois.
  • Ries, C., Y. Krippel, M. Pfeiffenschneider & S. Schneider, 2013. Environmental impact assessment and black, watch and alert list classification after the ISEIA Protocol of non-native vascular plant species in Luxembourg. Bull. Soc. Nat. luxemb. 114: 15-21. [PDF 652 KB]

 Page content last updated on 2020-04-29.