''Crassula helmsii'', known as swamp stonecrop or New Zealand pigmyweed, is an aquatic or semiterrestrial species of

succulent plant In botany, succulent plants, also known as succulents, are plants with parts that are thickened, fleshy, and engorged, usually to retain water in arid climates or soil conditions. The word ''succulent'' comes from the Latin word ''sucus'', meani ...

in the family

Crassulaceae The Crassulaceae (from Latin ''crassus'', thick), also known as the stonecrop family or the orpine family, are a diverse family of dicotyledon flowering plants characterized by succulent leaves and a unique form of photosynthesis, known as Crass ...

. 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 Register of Introduced and Invasive Species of eleven countries.

Description

The shoots are rather stiff, carrying narrow parallel-sided

leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

in opposite pairs, each leaf being about . Small white

flowers A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...

with four petals are produced in summer on long stalks arising from the upper leaf axils. The flowers are always above water.

Distribution

On the island of Ireland, ''C. helmsii'' has recently 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. It has been reported to be very tolerant to copper toxicity and to be a

hyperaccumulator A hyperaccumulator is a plant capable of growing in soil or water with very high concentrations of metals, absorbing these metals through their roots, and concentrating extremely high levels of metals in their tissues. The metals are concentrated a ...

of copper.

Cultivation

''C. helmsii'' is able to grow fully submerged in a cool-water

aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...

or as a submersed or marginal plant in a

pond A pond is an area filled with water, either natural or artificial, that is smaller than a lake. Defining them to be less than in area, less than deep, and with less than 30% emergent vegetation helps in distinguishing their ecology from th ...

. Once established it can grow vigorously and may need to be trimmed back. Schedule 9 of the UK

Wildlife and Countryside Act 1981 The Wildlife and Countryside Act 1981 is an Act of Parliament in the United Kingdom implemented to comply with European Council Directive 79/409/EEC on the conservation of wild birds. In short, the act gives protection to native species (especia ...

lists this plant as one that must not be caused to grow in the wild.

References

External links

''Crassula helmsii'' GBIF (images, distribution, invasive species status)

BioImages

Status in N. Ireland
includes an introduction on UK information
Flora of N. Ireland - illustrated

Ecological information
{{Taxonbar, from=Q160221 helmsii Flora of New Zealand Saxifragales of Australia Flora of New South Wales Flora of Victoria (Australia) Flora of Tasmania Eudicots of Western Australia Flora of South Australia Plants described in 1899 Taxa named by Thomas Kirk