Crassula helmsii
species of plant
Crassula helmsii, known as swamp stonecrop or New Zealand pigmyweed, is an aquatic or semiterrestrial species of succulent plant in the family Crassulaceae. Originally found in Australia and New Zealand, it has been introduced around the world. In the United Kingdom, this plant is one of five introduced invasive aquatic plants that were banned from sale from April 2014, the first ban of its kind in the country. It is on the Global Biodiversity Information Facility's Global Register of Introduced and Invasive Species of eleven countries.
Description
The shoots are rather stiff, carrying narrow parallel-sided leaves in opposite pairs, each leaf being about 4–24 millimetres (0.16–0.94 in). Small white flowers with four petals are produced in summer on long stalks arising from the upper leaf axils. The flowers are always above water.
Distribution
C. helmsii was recorded in 2010 throughout the British Isles, in the Netherlands, Belgium, the United States, Russia, France, Germany, Italy and Spain
In Ireland, C. helmsii has been recorded on waste ground in Ireland at Howth Head, County Dublin, and at a number of sites in Northern Ireland.
Ecological aspects
The plant grows on the muddy margins of ponds where it forms carpets with 100% cover, semi-submerged in deeper water, or totally submerged with elongated stems. It does not die back in winter.
This brief starts where responsible research should: with the source description of “Crassula helmsii” as species of plant. Everything that follows is an evidence route, not borrowed authority.
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The subject matters to the science & nature register because the source frames it as species of plant. Its deeper value depends on whether names, dates, institutions and citations support that framing.
Stable identifiers, scientific names and standards terminology offer the best bridge between this overview and specialist evidence. The source revision retrieved here is dated Aug 18, 2026. The linked authority identifier is Q160221. None of the 0 selected statements returned an explicit reference. The first chronological checks are 2014 and 2010.
A general summary may omit uncertainty, sample limits or methodological disagreement that is explicit in the technical record. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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This entry incorporates text from “Crassula helmsii” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.